 |
|
| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
| Reply |
|
|
LinkBack | Thread Tools | Display Modes |
|
|
|
#1
|
|||
|
|||
rack and pinion
The telescope I've referred to in recent postings has a pair of knobs joined by an axis whose center is a pinion that engages a rack on a tube that holds the eyepiece. This enables one to focus the telescope. The rack seems to be well-oiled but still moves somewhat unevenly in some places as one turns the knobs. When I look at it so that I can see all the teeth below me: ||||||||||| it seems that they have not all worn evenly, that some are apparently thicker than others, and that some of the valleys between them are more filled than others. I don't know if the latter condition indicates there is more oil in some than others or whether it indicates the presence of more dirt, which contributes to the uneven motion. The person who loaned it to me told me it would be ok for me to oil it and maybe that also means it is ok for me to clean it (e.g. with a toothbrush). But before I do anything, I'd like to be sure of what kinds of conditions contribute to this kind of uneven motion in a rack and pinion. It mostly turns evenly but in some places it seems more prone to offer some resistance. Leaving aside whether it would be permissible to make repairs on the borrowed scope, I don't know if it is possible to replace the rack. It seems to be riveted in place. I wouldn't know how to select a replacement rack or two replacement rivets. Maybe with suitable machines, I could make my own rack. That is something I would keep in mind for the future, when I have some machines and want to modify or build my own telescope. Continuing with the hypothetical, suppose I want to be really fanatical about figuring out what exactly is wrong with the rack. Since eyeballing it suggests some irregularities, suppose I want to measure all of the heights of the teeth and all of the widths of the peaks and of the valleys. Is there any convenient way to do this? One way that occurrs to me is to take the rack, clean it, ink it and press it against a piece of paper to make a print of the rack. Then I can photocopy the inked page with enlargement and measure it. There would still be a lot of measurements to make, but they wouldn't be so small and easy to mess up. Also, if the print were faint in some places, that would confirm my impression that it was badly worn in some places. There is one other issue related to the rack and pinion. There seems to be no barrier between the rack and pinion and the interior of the telescope tube. It occurs to me that this might let vapors from the oil diffuse into the tube and possibly also coat the inner surface of the telescope lens at the other end. That sounds undesirable and makes me wonder whether someone might have made a mistake by oiling the rack and pinion in the first place. If so, the source of the mistake might have been that someone noticed the uneven motion and resistance to turning, didn't realize the role that wear might have played in it, and instead tried to solve the problem by oiling it without realizing that this might be bad for the optics. On the other hand, I don't know anything about scopes or racks and pinions, so my 'pinions aren't worth anything. If someone is better informed, please inform me. Thanks. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#2
|
|||
|
|||
|
On 27 Nov 2004 02:18:57 -0500, Allan Adler
wrote: Clean the rack and pinion, making sure that there's nothing stuck in the root, the very bottom of the teeth. Uneven wear, or uneven spacing when the rack was made? Either are possible, Rack and pinions are available from Boston Gear, Browning and others. If it's older US made scope, no problem. If it's a newer import, Rotsa Ruck. Accepted lube is RT-44, using way oil or any other substitute is going to guarantee problems with lube migration, or shiny stains where you don't want them. IF you replace the rack, you might be tempted to use the nylon rack, bad idea, I've done it and it didn't take long to switch back to the brass. Rivetted sounds like an import, 0-80 screws are what I use. It ain't rocket science, pretty straight forward job. Helical focuser is also an option, and I've made a couple of those too, each has it's benefits and drawbacks. Personal preference there, neither has a clear advantage over the other unless you're putting a camera on the focuser, in which case the helical is out. |
|
#3
|
|||
|
|||
|
|
|
#4
|
|||
|
|||
|
On 27 Nov 2004 11:06:26 -0500, Allan Adler
wrote: It was made in Japan according to the specifications of Meade. I didn't see a date anywhere, but I know that it is at least 10 or 11 years old and probably more. Ok, newer import. But Meade supports their products pretty well, and it might be possible to just buy a new drawtube, with the rack already installed. Is there any convenient way to try to figure out, without damaging the telescope or screwing up its optical alignment, whether any lubrication has migrated into the telescope tube? If it has, is there a good way to clean up the mess inside? Maybe if I don't see any chromatic aberration or haloes, or something like that, when I look at the sky, all is well, but maybe the effects are subtler than that. The biggest problem wouldn't be coating the lens, but causing shiny places on the interior of the tube. It's generally noticable as a loss of contrast, more when looking at a bright object, the moon for example. If it's on the lens/mirror, it *may* cause haloes, or other abberations, but chances of it getting there are pretty slim, especially if the instrument hasn't been relubed with the wrong thing. I clean, relube, recollumate my three reflectors about three times a year, and there isn't too much you can do that isn't field adjustable to correct. If it's a refractor, they're almost impossible to screw up as long as you don't take the lens out of the cell. Once it comes out, unless you mark everything to make sure it goes back in exactly as it came out, all bets are off. Still, all it takes is marking so you know what came out when. Especially the front and back faces of the lens, in a non cemented lens, they can be reversed easily, and then comes the bitch of trying to figure out which one is reversed. A dot of water soluble marker can save hours of frustration. I don't actually know that they are rivets. I only know that when I look at the rack (not brass, by the way, but some grey metal), the brass things I see holding it in place don't look like screws. Could be a zinc alloy, not unheard of. Saves machining at the cost of a longer life. If they were screws, the heads would be instantly seen as such. Play in the rivets is also not unheard of, and sometimes can be frustrating when you're trying to focus that 6mm eyepiece. The higher the magnification, the worse small problems become. (Which is probably why my favorite EP is a 28mm plossl.) |
|
#6
|
|||
|
|||
|
In article ,
Allan Adler wrote: It's a refractor. I noticed that, where the lens is, there are 6 screws It's a refractor, and it's borrowed. Two good reasons not to mess with it. The latter because it's very irritating to find that something you've loaned out and mentioned that it would be OK to oil is "rebuilt" without your blessing. Especially if the rebuilding goes awry. The former because I'm about 99% certain that what you are describing (right down to the zinc rack) is a cheesoid "christmas and birthday telescope". The outside of the box prominently tells you it's 200x or 400x, it's got a wobby tripod which may have a low quality "polar" mount, the aperture is a whopping 3 inches or so, etc. These things have probably driven thousands of people away from astronomy. They never work very well, and you should be able to get your own at a junk shop, flea market, recycling center, goodwill or tag sale for very little money. Don't buy one new. You can waste as much time and effort as you would like tearing that apart, without annoying anyone. Don't expect a very satisfying viewing experience. If you actually want a telescope to look at the sky with, get a reflector with a "dobsonian" mount. A physics teaching acquaintance has 2 or 3 of the cheesy refractors (people donate them when they discover that they can't actually see all the stuff they thought they'd see), and one reflector (bought). There's just no comparison, the reflector is that much better - and not really much more expensive if bought new. You can also go the traditional route and grind your own mirror, if you like, or buy mirrors and build the rest of the scope (pretty easy). The mount is easy to build, as well. -- Cats, Coffee, Chocolate...vices to live by |
|
#7
|
|||
|
|||
|
On 28 Nov 2004 02:11:16 -0500, Allan Adler
wrote: You also clean the inside of the telescope tube? As far as cleaning out the spiderwebs, but all I do is run a dry towel through it for that. Mine are all reflectors. I do have a wide field made from a Kodak Aero-Tessar, but that lens is so heavy that I seldom use the instrument, Very difficult to balance it on the mount. The tube is some 20 inches long, not counting the focuser, and balances 3 inches behind the objective lens. Is there a good book that discusses all the things you can do to maintain a scope in good condition? Amateur Astronomer's Handbook, J.B.Sidgwick, Dover press 0-486-24034-7 Also Amateur telescope Making, Ingalls, but it's long out of print, might find a copy at a library. Scientific American Publishing, my copy is copyright 1935. If it's a refractor, they're almost impossible to screw up as long as you don't take the lens out of the cell. It's a refractor. I noticed that, where the lens is, there are 6 screws holding a metal piece that I figure probably clamps the lens in a certain position. The 6 screws are arranged in three pairs, with the three pairs placed 120 degrees from each other. Yes. Antagonistic screws, one will move the lens mount, the threads are in the mount, the other is the locking screw, the threads are in the part that is mounted to the tube. They should be snug, but not tight, excess pressure from them can distort the lens, or in really bad cases, crack it. Also a sign of a little better quality instrument, BTW. Even with the reflectors, collumination is a process of three interactive adjustments, the degree of perfection being dependent on your patience. I have cheaters methods I use in the field, probably not giving perfect collumation, but good enough for casual stargazing. Sidgwick covers it fairly well, but he also goes into making micrometers and other attachments that would require a higher degree of perfection than I do. |
|
#8
|
|||
|
|||
|
In article ,
wrote: [ ... ] Helical focuser is also an option, and I've made a couple of those too, each has it's benefits and drawbacks. Personal preference there, neither has a clear advantage over the other unless you're putting a camera on the focuser, in which case the helical is out. A double helical -- a tube threaded inside and outside -- one left-hand thread and the other right hand thread, with an inner tube connected to the camera and the outer tube connected to the telescope, and some kind of keyway to prevent rotation of the inner tube relative to the outer tube and you are fine. This is pretty much the way the focusing ring on SLRs is done. (Some older lenses on folding cameras had the front element on a single thread -- but that did not need to move as far to focus through the desired range. Moving the entire lens to focus takes more motion. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#9
|
|||
|
|||
|
|
|
#10
|
|||
|
|||
|
In article ,
wrote: On 27 Nov 2004 22:17:10 -0500, (DoN. Nichols) wrote: A double helical -- a tube threaded inside and outside -- one left-hand thread and the other right hand thread, with an inner tube connected to the camera and the outer tube connected to the telescope, and some kind of keyway to prevent rotation of the inner tube relative to the outer tube and you are fine. This is pretty much the way the focusing ring on SLRs is done. Nope. Focus ring is a nut, with a retainer to keep it from moving, the male thread is on the lens barrel. Usually 4 to 6 lead though, never single lead. Which means there are a lot of ways that it will go together, only one of which is right. That may be the case in the eyepiece focusing on a telescope, and for *some* camera lenses, but the longer the focal length, and the more desire for close focusing, the more likely the camera lens is to be with double helical. I have disassembled lenses of this sort, so I am sure that they exist -- even as short as 135mm focal length on a 35mm camera. The focus ring is tied to the ambisexual ring, with a female thread attached to the camera body, and a male thread attached to the lens cell itself, so you can move the lens cell a long distance without having to have a threaded sleeve the whole length of the travel. Yes, multi-lead makes for faster focusing, and is amost always found in SLRs at least -- and even in the very fine thread on the front element of a Zeiss 75mm f3.5 Tessar on a folding 120/620 roll film camera (16 shots per roll, with that short a focal length -- vertical format by default. That was my first camera with a reasonable quality lens. Suppose a helical focuser for a scope could be made that way, but most of them don't have a real thread as such, it's usually a radiused groove, and engages a ball indent for rapid focusing. I make mine like a very shallow acme thread, the groove just wide enough to take the ball, and deep enough so the ball almost touches the bottom. Parfocal eyepieces eliminate the need for the rapid, but add quite a bit to the cost. There are focusers available in just about any configuration anyone would want, if their wallet is heavy enough. The ball and groove one would work well enough for something light, like an eyepiece, but when you hang the weight of a camera body -- especially if it has a motor drive as part of it for semi-remote shooting -- you need something more sturdy, like a real thread. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#11
|
|||
|
|||
|
|
|
#12
|
|||
|
|||
|
Allan Adler wrote in
: big snip You might want to investigate the pinion. There may be nothing wrong with the rack at all. If the center hole on the pinion is offset, or at an angle to the teeth, this would also explain the uneven wear. Even a mis- alignment of the two bores the pinion rides in could cause this. -- Anthony You can't 'idiot proof' anything....every time you try, they just make better idiots. Remove sp to reply via email |
|
#13
|
|||
|
|||
|
Anthony writes:
You might want to investigate the pinion. There may be nothing wrong with the rack at all. If the center hole on the pinion is offset, or at an angle to the teeth, this would also explain the uneven wear. Even a mis- alignment of the two bores the pinion rides in could cause this. I ruled out a problem with the pinion on the grounds that the resistance wasn't repetitive as one turned the knobs completely a few times. I don't know if that is a valid argument. The pinion and the knobs form a single piece. So, unless it was made incorrectly, I don't have any reason to suspect the pinion itself. I'm not sure what you mean by "at an angle to the teeth". One meaning might be that it crosses the teeth. With that meaning, it might not work at all, so I'm guessing you mean that the planes containing the teeth of the pinion and of the rack are parallel but the peaks of the pinion are not parallel to those of the rack. To put it another way, I think you're saying that the axis of the knobs might not be parallel to the bottom line of the rack valley it passes through, so that it dips to one side. That is conceivable but again it would seem that it would result in consistent problems all along the length of the rack, not just in one place. On the other hand, there still might be a problem such as you describe. I unscrewed the "box" that covers the pinion. It is not perfectly rectangular, since it has to fit against the cylindrical tube and also it has cuts to allow the axis of the knobs to pass. I turned the box over, so that these cuts were all on top and the box was open, and noticed that there was a flat rectangular piece of metal inside of nearly the same length and width of the box. The rectangular piece had a rectangular hole in it. When I opened it, it was jammed in so as to run diagonally in the box from one edge on the bottom to the opposite edge on the top. There were two more identical pieces of metal sitting flat on the cylinder and the axis of the knobs, enclosing the little towers that the screws screwed into and the pinion. The bottom of the box has four "pedestals", one in each corner. I don't know whether the flat piece of metal was correctly placed. Possibly someone else opened it up to oil the pinion and put the flat piece back in incorrectly and possibly it is really supposed to be in the diagonal position in which I found it. If the three flat pieces are removed entirely, then the axis of the knobs wobbles badly. I think the three flat pieces are intended to sit flat on the four pedestals. When they are stacked that way, they fit in the box but rise to block off most of the hole the knob axis passes through. So, I think the flat pieces are used to clamp the knob axis in a fixed position. The flat pieces also rise above the bottom of the circular arcs that are intended to fit the cylinder body. I think that when the box is screwed back onto the cylinder, the flat pieces are forced down to the bottom of the circular arcs, forcing them to bend to conform more to the cylindrical shape. This has the effect of pushing the other two, still straight, edges of the flat pieces to clamp the knob axis even more tightly. This arrangement makes so much sense to me in terms of the operation of the rack and pinion that I find it hard to believe that the diagonal arrangement I found could possibly be correct, but maybe there is something I don't know, such as the possibility that the diagonal arrangement eliminates some lateral movement. I didn't find that correcting it, even if it was wrong, made any difference in the resistance, but this is all kind of subjective. Unfortunately, I can't see the pinion engaging the rack, so it is hard to know what the problem is exactly, except by trying something that has the effect of curing it and concluding that what I thought I was correcting was actually what was wrong. But I do have one idea: I can count how many teeth there are on the pinion and how many are on the rack and how much of a turn I have to make of the knobs to move a given number of teeth along the rack and how many teeth there are between the visible part of the rack and the part that actually engages the teeth. That means I may be able to wait until I find some resistance and then turn the knobs the appropriate amount to move the bad part of the rack to where I can see it. After I've gotten that crackpot idea out of my system, I'll probably just clean and re-oil it, as was suggested by others. But I'm still concerned about the possibility that oil fumes might be contaminating the telescope tube and coating the inside surface of the telescope lens. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#14
|
|||
|
|||
|
Allan, what if you ask for a digital camera for Christmas?
GWE Allan Adler wrote: Anthony writes: You might want to investigate the pinion. There may be nothing wrong with the rack at all. If the center hole on the pinion is offset, or at an angle to the teeth, this would also explain the uneven wear. Even a mis- alignment of the two bores the pinion rides in could cause this. I ruled out a problem with the pinion on the grounds that the resistance wasn't repetitive as one turned the knobs completely a few times. I don't know if that is a valid argument. The pinion and the knobs form a single piece. So, unless it was made incorrectly, I don't have any reason to suspect the pinion itself. I'm not sure what you mean by "at an angle to the teeth". One meaning might be that it crosses the teeth. With that meaning, it might not work at all, so I'm guessing you mean that the planes containing the teeth of the pinion and of the rack are parallel but the peaks of the pinion are not parallel to those of the rack. To put it another way, I think you're saying that the axis of the knobs might not be parallel to the bottom line of the rack valley it passes through, so that it dips to one side. That is conceivable but again it would seem that it would result in consistent problems all along the length of the rack, not just in one place. On the other hand, there still might be a problem such as you describe. I unscrewed the "box" that covers the pinion. It is not perfectly rectangular, since it has to fit against the cylindrical tube and also it has cuts to allow the axis of the knobs to pass. I turned the box over, so that these cuts were all on top and the box was open, and noticed that there was a flat rectangular piece of metal inside of nearly the same length and width of the box. The rectangular piece had a rectangular hole in it. When I opened it, it was jammed in so as to run diagonally in the box from one edge on the bottom to the opposite edge on the top. There were two more identical pieces of metal sitting flat on the cylinder and the axis of the knobs, enclosing the little towers that the screws screwed into and the pinion. The bottom of the box has four "pedestals", one in each corner. I don't know whether the flat piece of metal was correctly placed. Possibly someone else opened it up to oil the pinion and put the flat piece back in incorrectly and possibly it is really supposed to be in the diagonal position in which I found it. If the three flat pieces are removed entirely, then the axis of the knobs wobbles badly. I think the three flat pieces are intended to sit flat on the four pedestals. When they are stacked that way, they fit in the box but rise to block off most of the hole the knob axis passes through. So, I think the flat pieces are used to clamp the knob axis in a fixed position. The flat pieces also rise above the bottom of the circular arcs that are intended to fit the cylinder body. I think that when the box is screwed back onto the cylinder, the flat pieces are forced down to the bottom of the circular arcs, forcing them to bend to conform more to the cylindrical shape. This has the effect of pushing the other two, still straight, edges of the flat pieces to clamp the knob axis even more tightly. This arrangement makes so much sense to me in terms of the operation of the rack and pinion that I find it hard to believe that the diagonal arrangement I found could possibly be correct, but maybe there is something I don't know, such as the possibility that the diagonal arrangement eliminates some lateral movement. I didn't find that correcting it, even if it was wrong, made any difference in the resistance, but this is all kind of subjective. Unfortunately, I can't see the pinion engaging the rack, so it is hard to know what the problem is exactly, except by trying something that has the effect of curing it and concluding that what I thought I was correcting was actually what was wrong. But I do have one idea: I can count how many teeth there are on the pinion and how many are on the rack and how much of a turn I have to make of the knobs to move a given number of teeth along the rack and how many teeth there are between the visible part of the rack and the part that actually engages the teeth. That means I may be able to wait until I find some resistance and then turn the knobs the appropriate amount to move the bad part of the rack to where I can see it. After I've gotten that crackpot idea out of my system, I'll probably just clean and re-oil it, as was suggested by others. But I'm still concerned about the possibility that oil fumes might be contaminating the telescope tube and coating the inside surface of the telescope lens. |
|
#15
|
|||
|
|||
|
Grant Erwin writes:
Allan, what if you ask for a digital camera for Christmas? OK, Grant: Can I have a digital camera for Christmas? (How's that for grantsmanship?) -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#16
|
|||
|
|||
|
On 27 Nov 2004 10:51:04 -0500, Allan Adler
wrote: The shaft for the pinion floats in the "box", and the flat piece inside is the spring that keeps tension on it, keeping it fully engaged. Where the spring contacts the shafts, use a heavy grease, it's slow turning, but needs the lubrication. IF, when the pinion is fully engaged in the rack, the shafts hit the bottom of the slots, the rack is worn out. If it's not repetitive, then the pinion is probably reasonably concentric to the shaft, and the rack is the problem. In the older scopes, wear on the rack would take a very long time, but the newer ones sometimes have plastic rack, or soft brass, which will wear quickly. RT-44 is used because it does not outgass, it stays where you put it. Oil fumes on the mirrors are a legitimate concern, not fatal, but cause for cleaning and collumating more often than they should be. If the rack is worn, there is nothing that will even things out but a new rack. I would be more concerned if there was slop in the drawtube/focuser body fit. This is also compensated for by the flat spring in the "box". The spring should press the pinion into the rack, and also to one side of the slots the shaft runs in. |
|
#17
|
|||
|
|||
|
|
|
#18
|
|||
|
|||
|
On 28 Nov 2004 01:52:42 -0500, Allan Adler
wrote: I would be more concerned if there was slop in the drawtube/focuser body fit. As a matter of fact, there seems to be, if I understand you correctly to mean on the same surface that the rack is mounted to. It is mostly near the rack but "slop" is a good description of it. Ok. On some of the focusers, I don't know if Meade ever used it, there are flat springs opposite the rack, and they furnish friction to keep it from moving unless driven by the rack/pinion. If these are properly set, they will hold the drawtube in a sort of balance with the pressure of the rack, but will seem to be allowing movement, which in use will not be the case. The old 6" Edmonds has two felt strips opposite the rack, some have other methods, even going so far as to having eliminated the rack for a friction drive, and having ball bearings instead of springs or felt. The main thing is that with the eyepiece installed, it should be centered and with the optical axis also centered and parallel to the optical axis of the objective lens. If it was a cheaper focuser, and has the felt, chances are that the felt has compressed and is no longer holding it firmly. Quicky repairs can be made by replacing the felt, but I prefer to use the flocking from the film slit of a 35mm cartridge instead of felt. It seems to not compress as quickly, and sometimes gives a little more "solid" feel to the focuser. When you say "to one side", I think you mean either towards or away from the eyepiece. It should be holding it so the shaft can't move up or down or towards the drawtube easily. If it's too loose, it acts like backlash, or excess play when changing the directon you're moving the drawtube. There are as many variations in how it was accomplished as there are makers of telescopes, every one of them believing they have a "better idea." My own "better idea" would be a planetary drive fine focus knob, but due to the costs of making such an animal, maybe it wouldn't be worth it. I probably have ten or fifteen focusers in different stages of "maybe this will work" in the basement, but still have to come up with the "perfect" idea. It's pretty hard to improve on something that people have been working on for several hundred years. |
|
#19
|
|||
|
|||
|
I've been trying to follow up on details of some suggestions.
Regarding the threads in lens holders in eyepieces, the use of collapsing taps seems to be prohibitively expensive, although in searching for them the collapsing taps I've found don't seem to be for that range of sizes. On the other hand, one doesn't have to make them exactly the way they are made in commercial products. One reason given for the odd sizes was so that other things don't get screwed in by mistake. For making my own, I probably don't need to worry about that. There might still be a reason one wants very fine threads. One thing that occurred to me was that maybe by making multiple threads, one could achieve the same fineness. Alternatively, by using CNC one might just be able to tell the lathe exactly how to cut the threads. Hence, regarding CNC: it was mentioned that Nick Carter has some device called a Frog for upgrading a Taig lathe to CNC for about $200. I'm not sure what assumptions are made regarding the configuration about the Taig nor what assumptions are made regarding the computer to which the Frog is supposed to be able to be connected, if one wants to connect the Frog to a computer. To take an extreme example, suppose I find a vacuum cleaner discarded on the street and perform a motorectomy on it and order the K1019 deal at http://www.taigtools.com for $144.50 and one Taig Frog for $199 from Nick Carter. Then for a total of $344, more or less, I have a lathe and a Frog, but it's not clear to me whether there is enough Taig there to use the Frog with it. Obviously, one can't have the Frog tell the Taig to do stuff that requires a tailstock, but there are things one can do without a tailstock. (More on this below.) As regards the computer, will the Frog work with the computer if it is a PC running some version of RedHat Linux (as mine is)? I haven't taken any courses on lathes. I happened to read Joe Martin's book, Tabletop Machining, and I read Gingery's book, The Metal Lathe, and I have version 55 of the South Bend Lathe Book, from around 1958. In particular, Gingery shows you the lathe in various stages of completion and how to use it to bootstrap the rest of the lathe. So, I compared the parts list at http://www.taigtools.com/mlathe.html with what I found in Gingery's book, not too meticulously, but enough to give me some idea. The part list of the Taig Micro Lathe II kit mentions a bed but doesn't mention anything about ways. I think I'm supposed to realize that the bed includes the ways. In the Gingery lathe, there is a lead screw. I'm not sure but I think the analogous part for the Taig is 100-09, which is the carriage rack (there is also a pinion gear, so I think I am still within bounds of the subject "rack and pinion"). On p.100, Gingery writes: "At this point, you have built a lathe that is as complete as some that are sold commercially. If you have been in the market for a lathe very long, you are not surprised to learn that some lathes are sold without a tail stock. I could hardly call a tail stock an accessory, as some do, but the partially finished lathe can do many jobs now." Gingery declines to say what the jobs are that the partially finished lathe can do, but How to Run a Lathe says: "Work that cannot readily be mounted between the lathe centers is usually held in a chuck, as shown above, for machining." I assume that is meant to include the case where there is no tailstock. It goes on to mention, specifically: (1) taper turning with a chuck and compound rest and (2) cutting screw threads with a chuck and compopund rest, using gears that connect the headstock spindle to the lead screw." Maybe there are other things and maybe more can be done using the Frog with it, but I don't see it clearly. For example, I'm not sure what, in the case of the Taig, would take the place of the gears that engage the screw thread to achieve (2). Regarding the motorectomy, I'm reading the book, "Fractional horsepower motors: use, selection, operation, repair and maintenance", by Rex Miller and Mark Richard Miller. I'm about 100 pages into the book and a lot of just goes past me, but it has already discussed removing and repairing a vacuum cleaner motor. The book lists a lot of tools and parts one needs to get involved with motors, probably adding up to a significant investment, but I think the authors are assuming that anyone who reads the book is probably giving at least some thought to opening up a repair shop. What one actually needs just to scavenge one motor from a discarded vacuum cleaner for use with a lathe is probably not much. Incidentally, the micro lathe parts diagram and parts list at the Taig site seems to have a small typographical error: there is a part in the parts diagram labeled 100-28 but there is no such part in the parts list. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#20
|
|||
|
|||
|
In article ,
Allan Adler wrote: I've been trying to follow up on details of some suggestions. [ ... ] Hence, regarding CNC: it was mentioned that Nick Carter has some device called a Frog for upgrading a Taig lathe to CNC for about $200. I'm not sure what assumptions are made regarding the configuration about the Taig nor what assumptions are made regarding the computer to which the Frog is supposed to be able to be connected, if one wants to connect the Frog to a computer. To take an extreme example, suppose I find a vacuum cleaner discarded on the street and perform a motorectomy on it and order the K1019 deal at http://www.taigtools.com for $144.50 and one Taig Frog for $199 from Nick Carter. Then for a total of $344, more or less, I have a lathe and a Frog, but it's not clear to me whether there is enough Taig there to use the Frog with it. Obviously, one can't have the Frog tell the Taig to do stuff that requires a tailstock, but there are things one can do without a tailstock. (More on this below.) As regards the computer, will the Frog work with the computer if it is a PC running some version of RedHat Linux (as mine is)? O.K. The "frog" is not a part of Taig, or of Nick Carter. It was started by another person, who during the last year dropped the line and it was picked up by yet another. (I should remember the name of the latter -- from a mailing list in which I participate -- but I don't.) Have a look at this URL (which mentions Nick Carter, as he is the premier worker with the Taig. http://www.avatartools.com/ and this subpage shows one fitted to a Taig: http://www.avatartools.com/Merchant2...gory_Code=Taig Note that you do not *need* a computer at all. The frog contains a keypad to allow you to enter commands to it. (A computer is probably easier to save programs and re-load them -- especially if it takes a lot of keystrokes to enter the program. I don't know whether there is anything locking it into Windows, and I somehow doubt it. Just a simple text transfer should be sufficient. [ ... ] The part list of the Taig Micro Lathe II kit mentions a bed but doesn't mention anything about ways. I think I'm supposed to realize that the bed includes the ways. Yes. The ways are a steel dovetail, which is mounted onto a aluminum bed filled with concrete to minimize vibration and chatter. In the Gingery lathe, there is a lead screw. I'm not sure but I think the analogous part for the Taig is 100-09, which is the carriage rack (there is also a pinion gear, so I think I am still within bounds of the subject "rack and pinion"). Larger lathes have a rack-and-pinion to move the carriage under control of the handwheel, and the leadscrew is only used with the gearbox for threading and power feed (and on the better ones, power feed picks up rotation of the leadscrew through a keyway milled along its length, to drive a gear train connected either to the handwheel (for slow longitudinal feed), or the cross-feed crank (for facing). This reduces wear on the threads and half-nuts over the life of the lathe. Smaller machines may have a leadscrew which is only operated by a handwheel at the end of the bed, so it is very slow to go from one end to the other. The Unimat SL-1000 (and DB-200) were of this type. The Taig has only the rack and pinion, and the frog kit for the Taig is designed to work with this. According to the web page, if you want to use it with a Taig which has been retrofitted with a leadscrew, you want to order the Sherline kit, which suggests that the Sherline is similar to the earlier Unimat machines. On p.100, Gingery writes: "At this point, you have built a lathe that is as complete as some that are sold commercially. If you have been in the market for a lathe very long, you are not surprised to learn that some lathes are sold without a tail stock. I could hardly call a tail stock an accessory, as some do, but the partially finished lathe can do many jobs now." Gingery declines to say what the jobs are that the partially finished lathe can do, but How to Run a Lathe says: "Work that cannot readily be mounted between the lathe centers is usually held in a chuck, as shown above, for machining." I assume that is meant to include the case where there is no tailstock. It goes on to mention, specifically: (1) taper turning with a chuck and compound rest Limited to the length of travel of the compound. and (2) cutting screw threads with a chuck and compopund rest, using gears that connect the headstock spindle to the lead screw." Except that there is no leadscrew on the standard Taig. But, there are other ways to cut threads -- with the Frog driving the carriage. Maybe there are other things and maybe more can be done using the Frog with it, but I don't see it clearly. For example, I'm not sure what, in the case of the Taig, would take the place of the gears that engage the screw thread to achieve (2). The Frog monitors a sensor on the headstock of the lathe, which produces a pulse once per revolution. It times the delay between pulses to calculate the RPM, and then drives the carriage at an appropriate speed to cut the thread, It always starts just after one of the pulses, so the successive (deeper) cuts are made along the same track. It is possible to fit a lathe with two Frogs, interconnected, so you can turn tapers using that. Note that when turning with a chuck, and no tailstock, you are limited in the length of the workpiece extending beyond the jaws of the chuck. This must be limited to something like no more than perhaps three times the diameter, or the flex of the workpiece material will introduce errors. A tailstock, with a live (or dead) center can allow much longer cuts, as the workpiece is supported at both ends, and the bending moment of the middle makes it able to work beyond twice the maximum length when using just the chuck. There is also available a stead rest, which can support a workpiece some distance beyond the chuck, without needing a tailstock. Regarding the motorectomy, I'm reading the book, "Fractional horsepower motors: use, selection, operation, repair and maintenance", by Rex Miller and Mark Richard Miller. I'm about 100 pages into the book and a lot of just goes past me, but it has already discussed removing and repairing a vacuum cleaner motor. The book lists a lot of tools and parts one needs to get involved with motors, probably adding up to a significant investment, but I think the authors are assuming that anyone who reads the book is probably giving at least some thought to opening up a repair shop. What one actually needs just to scavenge one motor from a discarded vacuum cleaner for use with a lathe is probably not much. A Vacuum cleaner motor may not be a satisfactory one -- in part because it tends to be more of an open frame format than most others, and thus allows chips from the lathe to get into the motor, and possibly damage it. In the vacuum cleaner, it is protected by the bag or filter in the cleaner. Incidentally, the micro lathe parts diagram and parts list at the Taig site seems to have a small typographical error: there is a part in the parts diagram labeled 100-28 but there is no such part in the parts list. I have not looked at that, so I don't know. I seem to remember you mentioning the lack of a dog and a faceplate (somewhere in the trimmed text, I suspect). Note that as long as you can mount a center in the spindle and access it through the chuck, you can use a jaw of the chuck to drive a lathe dog. (And, you can *make* a lathe dog, if you can't find one of the needed size -- especially in these smaller sizes.) But -- there is a faceplate available for the Taig. One with T-slots, so you can bolt a workpiece to it which can't be held in the chuck, among other things. And a (small) faceplate is not that difficult to make, if you also have milling capability. Enjoy, DoN. P.S. I suspect that you would get more immediate positive feedback if you bought the Taig with as many accessories as you can. Making your own is best done for a later machine, if needed, when you have the skills needed. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#21
|
|||
|
|||
|
Thanks very much for answering my questions about Frogs and Taigs and other
details. I think I understand a lot better now. (DoN. Nichols) writes: Note that you do not *need* a computer at all. The frog contains a keypad to allow you to enter commands to it. (A computer is probably easier to save programs and re-load them -- especially if it takes a lot of keystrokes to enter the program. I don't know whether there is anything locking it into Windows, and I somehow doubt it. Just a simple text transfer should be sufficient. I just took a look at http://www.sourceforge.net and did a search for cnc and found a number of projects in progress aimed at using Linux for CNC. Apparently most of them haven't released any free software yet, but it is only a matter of time. One that has released some stuff is at http://sourceforge.net/projects/cnccodegen and is described as follows: "CNC code generator is a software to generate CNC codes (G & M codes) for maching operations like milling, drilling. At present CNC code generator is limited for end milling. we working on other machining operations like turning, drilling etc." Two items that look especially interesting are the OpenCNC, which simulates what happens when you run a program on a lathe and does some error checking, and the Linux Multiple-Axis Control Project. Unfortunately, neither has released any files yet, according to sourceforge. Meanwhile, maybe it's time I learned to read and write G code. I vaguely recall that there is something on this in Machinery's Handbook and it doesn't cost me anything to look at it in the bookstore. I seem to remember you mentioning the lack of a dog and a faceplate (somewhere in the trimmed text, I suspect). I searched for "dog" and "faceplate" separately in this thread at http://www.dejanews.com and only found your article mentioning them. But the information about them is still welcome. P.S. I suspect that you would get more immediate positive feedback if you bought the Taig with as many accessories as you can. Making your own is best done for a later machine, if needed, when you have the skills needed. I agree. I'm not in any way in a position to make my own. For one thing, I can't cast molten aluminum in a crowded apartment. I should be able to find enough space to do some work on a lathe when I get one, though. I was only mentioning Gingery's book because it enabled me to do a comparative anatomy of lathes in various stages of completion. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#22
|
|||
|
|||
|
Alan:
A couple of simple things you can do to "diagnose" the gear mesh. First thoroughly clean both rack and pinion. Do not polish, but be sure they are clean. Then, do a contact pattern check. This is simply applying some sort of compound to the entire rack and repeatedly running the rack end to end several times and reviewing the "pattern" left behind. Obviously, don't use too much or anything that will get into the optics. Any good grease will do. (On a side note the professional gear guys use colored componds similar to jewelere's rougue.) What you should see ( in a correctly functioning gear mesh) is a uniform pattern on both the rack and pinion through out the entire stroke (all the way round the pinion and full length of the rack). The pattern should be centered on both the rack and pinion and should be as wide as the narrowest member (either the rack or the pinion). You probably will not see a uniform pattern based on what you wrote. If you see the pattern move back and forth across the gears, then you have a misalignment of the pinion shaft (not 90 degrees to the rack). If you see the pattern move deeper and then shallower in the gears then either the rack is warped, or the pinion is ecentric, or you have excessive wear. Use a dial indicator to determine whether you have an alignment problem and deal with it accordingly if you find one. Alsi check to see if the top of either the pinion teeth or the rack teeth is contacting in the root of the mating gear. Rack wear is simple to check. Use a caliper and measure the pitch between any two teeth near either end of the rack (just like thread pitch). If two adjacent teeth are too close for you to measure then simply measure between any convenient number ot teeth (say three or four). Then repeat this measurement several times along the length of the rack paying special attention to the teeth in the middle of the rack. Shorter measurements indicate wear. The pinion can be checked for wear similarly. A helpful trick is to get two short pieces of wire the same diameter (No. 12 copper wire is good enough) and lay one wire in the root of one tooth pair and the other wire in the root of another tooth pair as close to 180 degrees as possible from the first pair. Measure the distance "over the wires". Now repeat this procedure with sucessive tooth root "pairs" all around the pinion You should get the same measurement every time (or real close). Smaller measurements indicate worn teeth. Hope this helps. "Allan Adler" wrote in message ... The telescope I've referred to in recent postings has a pair of knobs joined by an axis whose center is a pinion that engages a rack on a tube that holds the eyepiece. This enables one to focus the telescope. The rack seems to be well-oiled but still moves somewhat unevenly in some places as one turns the knobs. When I look at it so that I can see all the teeth below me: ||||||||||| it seems that they have not all worn evenly, that some are apparently thicker than others, and that some of the valleys between them are more filled than others. I don't know if the latter condition indicates there is more oil in some than others or whether it indicates the presence of more dirt, which contributes to the uneven motion. The person who loaned it to me told me it would be ok for me to oil it and maybe that also means it is ok for me to clean it (e.g. with a toothbrush). But before I do anything, I'd like to be sure of what kinds of conditions contribute to this kind of uneven motion in a rack and pinion. It mostly turns evenly but in some places it seems more prone to offer some resistance. Leaving aside whether it would be permissible to make repairs on the borrowed scope, I don't know if it is possible to replace the rack. It seems to be riveted in place. I wouldn't know how to select a replacement rack or two replacement rivets. Maybe with suitable machines, I could make my own rack. That is something I would keep in mind for the future, when I have some machines and want to modify or build my own telescope. Continuing with the hypothetical, suppose I want to be really fanatical about figuring out what exactly is wrong with the rack. Since eyeballing it suggests some irregularities, suppose I want to measure all of the heights of the teeth and all of the widths of the peaks and of the valleys. Is there any convenient way to do this? One way that occurrs to me is to take the rack, clean it, ink it and press it against a piece of paper to make a print of the rack. Then I can photocopy the inked page with enlargement and measure it. There would still be a lot of measurements to make, but they wouldn't be so small and easy to mess up. Also, if the print were faint in some places, that would confirm my impression that it was badly worn in some places. There is one other issue related to the rack and pinion. There seems to be no barrier between the rack and pinion and the interior of the telescope tube. It occurs to me that this might let vapors from the oil diffuse into the tube and possibly also coat the inner surface of the telescope lens at the other end. That sounds undesirable and makes me wonder whether someone might have made a mistake by oiling the rack and pinion in the first place. If so, the source of the mistake might have been that someone noticed the uneven motion and resistance to turning, didn't realize the role that wear might have played in it, and instead tried to solve the problem by oiling it without realizing that this might be bad for the optics. On the other hand, I don't know anything about scopes or racks and pinions, so my 'pinions aren't worth anything. If someone is better informed, please inform me. Thanks. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#23
|
|||
|
|||
|
"Kelly Jones" described very clearly and in great detail how I could make a thorough check of the condition of the rack and pinion on the telescope. I just have a few questions: Then, do a contact pattern check. This is simply applying some sort of compound to the entire rack and repeatedly running the rack end to end several times and reviewing the "pattern" left behind. Obviously, don't use too much or anything that will get into the optics. Any good grease will do. (On a side note the professional gear guys use colored componds similar to jewelere's rougue.) Is there some kind of common coloring one can mix with with "any good grease" to simulate the stuff the professional gear guys use? For example, how about adding a tiny bit of alizarin crimson or emerald green oil paint to the grease? -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#24
|
|||
|
|||
|
On 30 Nov 2004 01:28:24 -0500, Allan Adler
wrote: "Kelly Jones" described very clearly and in great detail how I could make a thorough check of the condition of the rack and pinion on the telescope. I just have a few questions: Allan, as so often happens in this group, most of them have gone off the deep end again. You do not have to do a pattern check on the rack and pinion, that is for precision gearing, and precision gearing is not found in focusers under the $250 range. THe pinion is probably cut from extruded pinion wire rather than being a cut gear. The rack, if it's a gray metal as you describe, is die cast zinc, and no degree of precision there either. It simply is not needed. The optical comparator is massive overkill, just looking at the teeth with a good hand lens will show the problem if it's bad enough to cause a real problem. The racks and pinions in my old Edmonds are now over thirty years old, were never the epitome of quality to begin with, and don't cause any problems in use. If I were using one of the remote focusing units, the backlash might be a problem, but as I focus "eyeball to the eyepiece", it is not. Lube, I lube the drawtube, but grease and oil only attract dirt to cling in the rack, so mine runs dry except for the shaft and the drawtube itself. My final advice, put it back together, take it out and use it. If nothing else, it will give you far better views than the telescopes of Galileo, Herschel, Newton and others. IF the drawtube moves when you turn the knob, it's doing what it's supposed to do. A lot of time can be taken with technicalities, without looking at practicality. And already has, the prime question is "can I get this thing in focus", and if the answer is yes, going deeper into it is only wasting time and money. Your time would be better spent in a dark place, with the scope, even just sweeping starfields to see what is there that you can resolve with the instrument. Have fun. |
|
#25
|
|||
|
|||
|
Off the deep end? Perhaps. But the original question was about how to
check the rack and pinion, not whether it should be checked. I appreciate you pragmatisism, but it was still fun to describe how to do a pattern check. Whare's your sense of humor?  wrote in message ... On 30 Nov 2004 01:28:24 -0500, Allan Adler wrote: "Kelly Jones" described very clearly and in great detail how I could make a thorough check of the condition of the rack and pinion on the telescope. I just have a few questions: Allan, as so often happens in this group, most of them have gone off the deep end again. |
|
#26
|
|||
|
|||
|
On Tue, 30 Nov 2004 18:34:19 -0800, "Kelly Jones"
wrote: Off the deep end? Perhaps. But the original question was about how to check the rack and pinion, not whether it should be checked. I appreciate you pragmatisism, but it was still fun to describe how to do a pattern check. Whare's your sense of humor? My sense of humor disappears very quickly when it goes from the realm of the ideal to the realm of the ridiculous. A patten check on the hypoid diff gears that I used to do by the dozens is one thing, on a rack and pinion, where the rack is die cast and the pinion extruded is senseless. I could have gone into the whole nine yards of a gear lab check, but to what end? In this particular application, if the spur gear has .0002" helix, and the involute error is .001", what's the difference? Even pitchline to pitchline makes no difference here, the pinion is crushed into the rack for full engagement by a spring, and the relation of the pitchlines really don't mean squat. DP of the rack and pinion is going to be probably 32 or finer, you're looking for errors that are going to be in ten thousandths, and even if they're found, they won't bother anything. Even my 35 year old Edmonds, the focusing isn't perfectly smooth, but it doesn't make one bit of difference, it still works just fine. There are some focusers out there that are perfectly smooth, or as near as is possible, but at $300 or so per copy. To what end? The mirror in my 10" f8 cost me $350 for figuring and coating, I don't think a $300 focuser is going to make it work any better. It has an off the shelf Boston rack, and the pinion cut from pinion wire. Works just fine, and a hell of a lot cheaper. Why complicate things? |
|
#27
|
|||
|
|||
|
In article ,
Allan Adler wrote: The telescope I've referred to in recent postings has a pair of knobs joined by an axis whose center is a pinion that engages a rack on a tube that holds the eyepiece. This enables one to focus the telescope. The rack seems to be well-oiled but still moves somewhat unevenly in some places as one turns the knobs. When I look at it so that I can see all the teeth below me: ||||||||||| it seems that they have not all worn evenly, that some are apparently [ ... ] I'd like to be sure of what kinds of conditions contribute to this kind of uneven motion in a rack and pinion. It mostly turns evenly but in some places it seems more prone to offer some resistance. [ ... ] Continuing with the hypothetical, suppose I want to be really fanatical about figuring out what exactly is wrong with the rack. Since eyeballing it suggests some irregularities, suppose I want to measure all of the heights of the teeth and all of the widths of the peaks and of the valleys. Is there any convenient way to do this? One way that occurrs to me is to take the rack, clean it, ink it and press it against a piece of paper to make a print of the rack. Then I can photocopy the inked page with enlargement and measure it. There would still be a lot of measurements to make, but they wouldn't be so small and easy to mess up. Also, if the print were faint in some places, that would confirm my impression that it was badly worn in some places. What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). Mount it so you see the rack teeth in profile. Put some clear plastic film under the clips on the display, select the largest magnification you can manage with the optical comparator, and trace the outline of the profile on the plastic film. Now, move to one of the worst teeth, adjust so the bottom of the tooth profile is the same, and trace this one, The area between the two profiles should give you a good idea how badly worn it is. To *make* one, the ideal way (with HSM tooling) would be a horizontal milling machine, a proper gear tooth profile mill (for the rack gear -- which is either #8 or #1 -- I forget which end is correct, but when you buy it you can look that up in the catalog. One end of the set is for 135 tooth through rack, and the other end is 12-13 teeth. Obviously, you first have to know what the size of the rack teeth are -- both diametrical pitch (or "module" for metric gears, IIRC), and the pressure angle. And if the teeth are cut at an angle instead of straight across the gear (more like "/////////" than "||||||||") you will need to angle the blank, and to calculate a correction factor to your feed using a bit of trig to get the tooth spacing to come out right. Note that the angled teeth are a lot smoother in the feed, but you will need better bearings on the pinion, as it will have a side thrust which the straight tooth will not. Now -- if you want to avoid the side thrust, but benefit from the smoothness, then a herringbone gear would be ideal -- but more difficult to make. It would look somewhat like this: / / / / / / / / / / / / / \ \ \ \ \ \ \ \ \ \ \ \ \ There is one other issue related to the rack and pinion. There seems to be no barrier between the rack and pinion and the interior of the telescope tube. It occurs to me that this might let vapors from the oil diffuse into the tube and possibly also coat the inner surface of the telescope lens at the other end. That sounds undesirable and makes me wonder whether someone might have made a mistake by oiling the rack and pinion in the first place. If so, the source of the mistake might have been that someone noticed the uneven motion and resistance to turning, didn't realize the role that wear might have played in it, and instead tried to solve the problem by oiling it without realizing that this might be bad for the optics. The typical lube used in the focusing rings of cameras (multi-start threads) is typically a quite thick grease, and has fairly minimal vapor -- unless it is kept in the direct midsummer sun. :-) On the other hand, I don't know anything about scopes or racks and pinions, so my 'pinions aren't worth anything. If someone is better informed, please inform me. Thanks. Well -- you have most of what I know about the subject above. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#28
|
|||
|
|||
|
Donald Nichols wrote: What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). I looked in my optics books and didn't find "optical comparator", so I did a google search and found some information about it. Based on that, I'm wondering whether an old microfilm reading machine I fished out of a dumpster could be adapted for this purpose. It's housing is made of wood, the optics are in metal and it is intended for strips of microfilm, but I did manage to look at some crystals with it. It's a piece of junk but I've been reluctant to give up on it. The point is moot at the moment since it is in storage where I can't get at it, but I expect that situation to change. Even so, I'll need to acquire more practical knowledge about optics than I have at the moment before tackling it. This would be a lot cheaper than buying a comparator, I think, which would probably cost more than a new scope. But I'm looking forward to trying out this comparator idea for checking out the rack. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#29
|
|||
|
|||
|
In article ,
Allan Adler wrote: Donald Nichols wrote: What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). I looked in my optics books and didn't find "optical comparator", so I did a google search and found some information about it. Your'e unlikely to find them in an optics book -- but a well-equipped machine shop is more likely to have one. Based on that, I'm wondering whether an old microfilm reading machine I fished out of a dumpster could be adapted for this purpose. It's housing is made of wood, the optics are in metal and it is intended for strips of microfilm, but I did manage to look at some crystals with it. Those tend to have more magnification, and less depth of field than an optical comparator for machine shop work. Also, the screen tends to be a bit awkward to get to to add a transparent sheet to draw on. The one I have apparently came with optional lenses for 10X, 20X, and 40X, but I only have the 20X lens. A proper one has a collimated illuminator, a stage on which the object under test resides (with X and Y motion to move the viewpoint, plus Z for the focus. Usually, there is a way to measure the X and Y motion -- either with big micrometer heads to move the stage, or with dial indicators to measure the motion. However, there are minimal ones which are handheld, including a set of reticles to measure various things including small threads, and angles, an eyepiece, and a tube to join them. eBay auction #3855942073 has a set of reticles, but not the eyepiece and tube. I'm not sure, but I think that the price there is a bit high. Reliable tools has a nice looking one up for auction #3856418973, but it's heavy (300 pounds), and is certain to go higher, as there are over four days left. There is another by Nikon which is still within reason, and it suggests an alternative name "Profile Projector" for the equipment. (Auction #3856039570). I don't see any of the lightweight ones like mine -- it *looks* heavy, but is mostly blown plastic shell and a wood base. The size is necessary to get enough optical length for good magnification. Note that it *will* take up a lot of benchtop space. Try eBay searches for "optical comparator" (with the quote marks) and one will show up sooner or later. A reasonable price is somewhere in the $200-$300 price range. Unfortunately, this type is not there at the moment. Note that the same comparator shows up in the MSC catalog and in sales flyers for significantly more -- reasonable for a business, but not for a hobbyist. The brand on mine is "Micro-Vu", and the one on the MSC offering is Fowler, IIRC. It's a piece of junk but I've been reluctant to give up on it. The point is moot at the moment since it is in storage where I can't get at it, but I expect that situation to change. Even so, I'll need to acquire more practical knowledge about optics than I have at the moment before tackling it. This would be a lot cheaper than buying a comparator, I think, which would probably cost more than a new scope. But I'm looking forward to trying out this comparator idea for checking out the rack. If you want to try to make one, the general design involves: 1) Illuminator on one side of the stage (or below it with a transparent stage). (Plan on something like one of the Quartz Halogen projector lamps in their own parabolic reflectors so you have adequate brightness for good visibility in a well-lit shop. Remember that the more the magnification, the less the brightness remaining. 2) Moving stage for the device under test. 3) Lens to focus the image onto the screen. 4) Angled mirror in the back to bounce the image back and up towards the screen. 5) Round ground glass screen with reference lines (cross hairs plus angle lines and radius lines engraved in the glass, and filled with black paint. 6) Ring surrounding the ground glass screen, with a full 360 degree angle scale on it, and a vernier scale adjacent to it to allow measuring to fifteen minutes or so. 7) Spring fingers (similar to those which hold slides on cheap microscopes. These are used to hold the transparent films, either for hand drawing to compare worn and unworn teeth, or printed in a plotter from a computer, or photographically printed, to compare new parts to their designed profile for quality-control inspection. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#31
|
|||
|
|||
|
In article ,
Gunner wrote: On 30 Nov 2004 02:25:01 -0500, (DoN. Nichols) wrote: You're unlikely to find them in an optics book -- but a well-equipped machine shop is more likely to have one. [ ... ] business, but not for a hobbyist. The brand on mine is "Micro-Vu", and the one on the MSC offering is Fowler, IIRC. I have a spare Micro-Vu that Id let go really cheap. Screen is in excellent condition, but the light source was removed for some reason. Power transformer is fine as is the staging. Might be a good place to put on a nice bright LED light source. Or build one around one of the Quartz Halogen projection lamps with built-in reflector. Some of them (usually marked 82 V IIRC) are designed to run from the AC line fed by a single rectifier diode. No big transformer to deal with. But then again, the transformer in the back helps counterweight the optics, stage, and lens at the front. No dial indicators, clamp your own on. Of course -- but provisions for mounting them. I've put a 5" travel one on the X-axis on mine. Out of curiosity, do you know which lens yours has? Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
|
#32
|
|||
|
|||
|
I'm trying to follow up on Nobody's suggestion that I use RT-44 as a lubricant for the rack and pinion on the telescope. Searching for RT-44 with Google turns up endless hits for places on Route 44. At Ace Hardware's website, searching for lubricant turns up what looks like mostly motor oil but no RT-44 and searching for RT-44 turns up nothing. I also searched rec.crafts.metalworking for messages mentioning rt-44 and found two, one of which was Nobody's posting I'm following up on and the other was from someone who said he had gotten a tube from American Science and Surplus. Searching http://www.sciplus.com for rt-44 no longer turns up anything, nor does searching for lubricant. So, where does one get rt-44? -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
|
#33
|
|||
|
|||
|
On 07 Dec 2004 01:07:45 -0500, Allan Adler
wrote: So, where does one get rt-44? Probably not much help, but I got mine from American Science and Surplus, but their supplies of it are sporadic at best. They don't list it as RT-44, don't think they have any idea of what they're selling there. I'll take a look and see if they have anything listed, the last time, all they said, "It's slippery". The tube I got from them appears to be about a 50 year supply, and cost a whole buck. I think that when it's sold under the trade name, they're not so generous, but only tiny amounts are needed. IF all else fails, try J&H Microscope Repair Service in Madison, Wisconsin. I know Jerry keeps a pretty good supply. Just tell him Richard from Burlington steered you there. Don't have his phone handy, every time I call him I end up with some damn work I don't really want anymore. |
|
#34
|
|||
|
|||
|
|
| Reply |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| Panasonic K-Mechanism adjustment | Electronics Repair | |||
| Update to web site and possible gloat. | Metalworking | |||
| Various bandsaw questions...long | Woodworking | |||
Hybrid Mode
