In article ,
Glenn Lyford wrote:
Hi all,
Not having immediate success (but by no means having tapped out
all available vendors or sources yet, either) I have not yet found
suitable gears to feed the quick change gear box on the Hendey.
It has been several days since you posted this, and I have until
now only seen the followups, not the original.
I did in the course of poking through some of my boxes come
across a 3"OD x 6" long hunk of 6061-T6 aluminum (aluminium for
those across the pond).
This is where the insanity comes in:
I have two 72T 14DP gears. If I had two 36T 14DP gears, I should
in theory be able to generate all the speeds I need for my gearbox.
If I had 3 or 4, I'd even have extras for idlers. These are 14.5 deg.
pressure angle gears. I also have a 90T gear to also use for idlers.
Hmm ... before I get into the rest of this -- note that the
formed gear tooth cutters are available from places like MSC for fairly
reasonable prices. For example, I have just completed my set of 16 DP
14.5 Degree Pressure angle cutters -- buying two at a time, for the gear
pitch used in my Clausing 12x24" lathe. The ones which I got were
selling for $23.62 each -- and most of them were made in China, but
appear to be good milling cutters.
[ ... ]
All I really need to create approximate gears is a form tool, it
doesn't have to be one for horizontal milling, be it disk type or
fly cutter type. Why not a single lip milling cutter, aka, form
ground D-bit?
I'm not sure how well such would work, but it would be an
interesting experiment. It would probably work better in the aluminum
than it would in a proper material for the gears. (I'll go into that
more somewhat later in this followup.)
Glenn Ashmore just made a simple taper one for his
grinding fixture with apparent success. Probably grind one up out
of a broken tap or drill bit, and use the ultimate reference for
tooth form, one of the tooth spaces of the existing gears.
Note that ideally, the tooth form varies with the number of
teeth on the gear, so you should use a gear which already has the proper
number of teeth as the reference. The gear tooth cutters in the set are
split into eight to cover the whole of the range of reasonable
teeth, with the ones with smaller numbers of teeth covering the smallest
range of tooth counts, as the shapes change more rapidly with the lower
number of teeth.
Chuck
the bit of rod in a hand-held drill, and rotate it against the
grinding wheel. Once happy with the form as compared with the
master gear, grind off half to form the cutter.
As others have mentioned, -- what about forming the relief on
the cutter's form?
Next, drill and bore my blank for 1", and turn to 2.571 OD. Not
likely I'll hit either exact, but hopefully well enough for this
exercise. And by doing them both in one set-up, I'll not be relying
on my decrepit 3-jaw for accuracy.
Agreed.
Once removed, mount the blank on a 1" arbor. Will probably use one
or both of a filed keyway and/or a tapped hole for a set screw (or
even 2?). Mount 1" arbor in boring bar holder, on center line, of
my 200 series tool post. On the other end, mount keyed 72T gear to
use as an index with an improvised locating pin. Use the boring bar
clamp to resist rotation and not put too much load on the pin.
This is not bad -- but a modification of this could mount the
axis of the gear either vertical (with the reference gear above the
workpiece -- but this would require a vertical slide -- e.g. a milling
adaptor for the lathe), or horizontal, with the axis above the spindle's
axis to clear the cross-slide, which would allow the cross-feed to be
used to feed the blank through the intersection with the cutter --
either a standard gear tooth mill, or a fly cutter with a form ground
tooth profile. (Hmm ... you would still need a vertical feed to adjust
the depth of cut.
I presume that you will be skipping every other tooth on the 72
tooth master. I would suggest that you fill alternate teeth with layout
blue before you start, so you can identify which ones to use for
indexing.
Either buy or improvise an end mill holder (4MT), and mount the cutter
in the spindle.
An MT-4 blank should be large enough to machine a step and a 1"
diameter to hold the gear cutter -- if you use a gear tooth mill for the
purpose.
Set the blank axis at the proper final gear depth.
Set a feed stop. Feed the blank past the cutter with the crossfeed,
increasing infeed in several passes until I reach the stop for each
tooth space, then re-index.
Reasonable. Ideally with a keyway to lock both the workpiece
and the reference gear in place -- which you already mentioned as a
possibility.
The big advantage of this setup would be that it does not require
either a milling machine or a milling adapter for the lathe, just the
boring bar holder, and other pieces I already have on hand.
Plus some adaptation of the boring bar holder to allow mounting
of the index pin holder.
Possible pitfalls: Running out of crossfeed distance to finish across
the gearblank faces. Not having enough room to use the 72T gear
without it hitting the saddle as I infeed.
How long are you planning to make the shaft? You could make it
long enough to put the reference gear far out of the way (at some
tradeoff of rigidity.
Losing index and messing
up gear spacing,
Hence the need for the keys on both gears -- and the suggestion
of layout dye to identify which teeth you are allowed to use as index
references.
either by bending the locating pin or poor clamping
or rotating the index gear or the gear blank on the arbor.
Turn the nose of the index pin to the tooth form, so it offers
the maximum contact while milling. Harden and temper it to reduce the
chance of deformation during cutting stresses. (Or use a section of
rack gear of the right pitch mounted to the nose of the pin so you have
lots of contact surface.)
Use keys on both the reference gear and the workpiece.
Mangling
or breaking the cutter with poor selection of milling feeds or speeds.
This may be the greatest problem -- along with chips causing the
cut to be oversized, since the D-form will not spend enough time clear
of the cut to keep the chips out of the game.
Trying to cut without noticing the cutter has become dull (how do you
resharpen a D-bit form cutter, anyway?).
At a guess -- start out with the remaining material covering 200
degrees or so, with radial lines in to the center. Sharpen by grinding
back the leading edge.
Mangling my cutter beyond
repair before I get all the blanks cut.
If you consider this to be a likely problem, make more than one
before you start. Probably not a problem in 6061, but I suspect that
you will have more problems with a reasonable material for the gears.
Before I get any cut. Before
I get all the tooth spaces on one gear cut. Better to risk everything
and cut all the blanks at once? Or better to risk the cutting edge
dulling and cutting one blank at a time?
Since the life of the cutter is in question, do one at a time,
so you minimize the number of blanks you mess up if something does go
wrong. (If you were making these with standard tooling, on a standard
machine, there would be a good argument for making them in a group, of
course.)
Maybe one to learn on, then
the rest as a group?
Based on the luck with the cutter on the first?
You'll want something like kerosene, or WD-40 as a cutting
lubricant when cutting aluminum. For other materials, you will want to
change the lubricant as appropriate.
I should at least have enough stock for two or
three tries, depending on how many gears I want to end up with.
Given that I'll be cutting aluminum and not steel or cast iron, am I
likely to have sufficient rigidity and cutter life to complete this?
Probably -- but I don't think that you really *want* to make
that many gears.
Any other obvious or not-so-obvious pitfalls I'm overlooking?
And last but not least, am I likely to run into problems running
6061 gears with cast iron gears in the gearbox feed train?
Yes -- the aluminum is too soft (even the 6061T6) to operate
meshing with cast iron or steel gears at the power loads in a threading
geartrain, and you will wind up with the aluminum transferring onto the
steel or cast iron gears, making them a poorer fit to other proper
gears.
You may want to *try* the first gears with 6061 and test them
for fit -- but not use them for any cutting. Once you have done this,
you can even switch to one of the aluminum ones for the reference gear,
and thus eliminate the problem of accidentally not skipping the right
number of teeth. (But this means that you will need the pin to be
adjustable to handle the different radii of the two gear sizes.)
So give it to me straight, guys, how insane am I to even consider
this? I note that broken drill bits are essentially free, and the
chunk of 6061 cost me maybe $3 at a flea market.
As others have mentioned -- the broken drill bits are not
hardened in the shanks, which is where you would find the proper
starting shape for forming your D-cutter (if that is what you feel you
must use. I'm not sure, but I *think* that drill bits may even be two
part, with the flutes being HSS, and the shank mild steel. As others
have suggested, drill rod is inexpensive (36" lengths), and can be
nicely hardened after turning to near shape. You then grind to final
dimension, since the hardening process usually introduces some
distortion.
Have I mentioned
yet that this would be my first project on the lathe?
This makes it an ambitious learning experience.
Best of luck,
DoN.
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