Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John

John D'Errico wrote:
Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John

What are the other dimensions of the bar and how is it oriented and
mounted?

dennis
in nca

Hi John,

It could have been an internal stress that just worked its way out over
time. If I had to guess, I would suspect that the makers chose cold
rolled low carbon steel (1018 or maybe even A36). The stuff is great
for welding, has a mill finish good enough to avoid any further
machining, and it's pretty cheap. But, cold working the steel produces
a great deal of internal stress. A good ME or Machinist knows to stay
away from it for anything that needs to be dimensionally stable.
Better to use hot rolled steel because it ends up being a lot more
stable. Some (like myself) would refer to this as a "design defect"
because a different material should have been spec'ed for the
application. Alas, it's likely that the cost of materials outweighed
engineering sensibilities.

Or, then again, I could be wrong. Even hot rolled steel can have
internal stresses. It's a lot less common than cold rolled steel but
it can happen. Stress relieving involves a rather lengthy heat
treating process which would probably be out of the budget for such an
application.

Bending the bar back using the "arm strong" method will likely inject
some more stress (you are cold working it). So, don't be too surprised
if it bounces back again. If you can heat the bar up to a dull red
(1000F - 1200F), straighten it, and then let it cool slowly (like in
the furnace) then it should be OK. Or, have a new bar machined from
some hot rolled steel.

Ed Bennett

http://www.ts-aligner.com

John D'Errico wrote:
Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John

In article . com, "rigger" wrote:

John D'Errico wrote:
Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John

What are the other dimensions of the bar and how is it oriented and
mounted?

dennis
in nca

Its 3/8 x 3/4 x 20 (inches)

Mounted to the miter gauge at one end by two screws,
one about 2 inches from the end, the other at roughly
4 inches from the end.

John

In article , John D'Errico
wrote:

Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John


I'm starting to think that I know what happened.

When I withdraw it from the t-track on the saw table,
the front end is captured in the track by a "washer".
This prevents it from lifting during use. But when I
take it off the table to use a different tool (like a
tenoning jig or a panel cutter) I pull it out towards
me.

The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

This feels like the probable cause to me as I think it
over. If so, the solution for the future is simple.
Slide it forward first to release the washer from the
t-slot, then lift it.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?

John

"John D'Errico" wrote in message
...


The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

This feels like the probable cause to me as I think it
over. If so, the solution for the future is simple.
Slide it forward first to release the washer from the
t-slot, then lift it.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?


Stress relief? If you did bend it as you suspect then there is no stress to
relieve. Just bend it back. It's not like you are likely to distort the
steel. You could heat it to bend it back, but you will likely end up
causing more damage to the shape of it than if you just finish bending it
back into shape as you have already done. Heat is a great friend of working
metal, but if you don't know what you are doing or are not careful, that
heat and the associated benefits can turn around on you and all you end up
with is an interesting twist on a theme.

From what I've read John, you're trying to make too much of this problem.
Just bend it back and carry on.

--

-Mike-

"John D'Errico" wrote in message
...
In article
,
John D'Errico
wrote:

Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John


I'm starting to think that I know what happened.

When I withdraw it from the t-track on the saw table,
the front end is captured in the track by a "washer".
This prevents it from lifting during use. But when I
take it off the table to use a different tool (like a
tenoning jig or a panel cutter) I pull it out towards
me.

The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

This feels like the probable cause to me as I think it
over. If so, the solution for the future is simple.
Slide it forward first to release the washer from the
t-slot, then lift it.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?

John

Just bend it back....as long as it slides well, thats all there is to it.
Not exactly a super critical application. And take the stupid washer off
the end....does nothing useful in actual use and as you've discovered it
makes it harder to put the miter gauge on and off.

Jeff

John D'Errico wrote:
In article , John D'Errico
wrote:

Yes, I know that some might call this a woodworking problem,
some metal.

A few weeks ago I noticed that the miter bar for the miter
gauge on my table saw was bent. There was a bow in it of
about 3/16 of an inch over a 20 inch length. Its a steel
bar, not aluminum, for an Accu-miter gauge.

I know that I've never dropped it or abused it, so I'm
wondering how it bent. I find it hard to believe that
a 30 degree F temperature variation over the course of
some years would do this, and given what it took for me
to bend it back, I know that I've never subjected it to
that much punishment.

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

Since others don't use my shop, any guesses what happened?
Stress relief over 10-15 years of use?

Thanks,
John


I'm starting to think that I know what happened.

When I withdraw it from the t-track on the saw table,
the front end is captured in the track by a "washer".
This prevents it from lifting during use. But when I
take it off the table to use a different tool (like a
tenoning jig or a panel cutter) I pull it out towards
me.

The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

This feels like the probable cause to me as I think it
over. If so, the solution for the future is simple.
Slide it forward first to release the washer from the
t-slot, then lift it.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?

John

Yep 3/16 inch bend in a 20 inch length means that
somebody bent it. Your description sounds like
you found the problem. Personally I would throw
that washer away, then you could lift the bar out
any time you wanted (unless there are other
considerations, since I have never used a saw with
a T slot). There is absolutely no reason to
consider a new bar (a steel bar isn't going to
exhibit any kind of movement from stress, What
stress?. The only thing that will make it move is
temperature change and you will never detect that
and it won't affect anything you do. If the bar
now lies flat on your table top, you are good to
go. If not give it a few appropriate tap (not
against the table) to get it to lie flat within a
few mils.

"John D'Errico" wrote in message

To bend it back, I had to put it in the tail vise on my
bench between three pieces of drill rod, then crank down
to bend it almost 1/2 inch the other direction. After
4 passes or so at this, I've got the bow down to about
1/16 inch, as measured by a good straightedge.

And don't forget that either now or later on if it starts to get a little
loose, you can peen the edges some to tighten it up so it's workable.

Hmmmm.....

Well John, as you know, from your experience of trying to bend back the
bar, even dead soft cold rolled low carbon steel is very elastic at
room temperature (modulus of elasticity is something like 29*10^6 psi).
It seems unlikely to me that the pressure of removing your miter gauge
from the slot, even many times over many years, would result in
gradually bending the bar as much as you say (50% of the thickness). I
would expect the washer to have suffered far more damage - especially
since it's considerably thinner and on the short end of the lever. The
process you have described would be best referred to as repeated stress
and the results would be dependent on the plastic properties of the
material.

In spite of opinions to the contrary, I'll stick by my original
assessment. Stress relief (not "stress", as others have misstated) is
the most likely cause. I base this assessment on many years of
metalworking. I can easily understand why someone with little or no
experience with CRS might consider it a ludicrous theory. If, like one
of the responders, you consider your table saw to be a crude machine
which is incapable of anything better than rough work, then just bend
it back and don't give it a second thought.

Bending it cold will be a lot easier if you use an arbor press. You
can improvise one by suspending the bar between two blocks along the
edge of a table or bench. Then use a "C" clamp in the middle between
the top of the bar and the underside of the table or bench. Using this
setup will give you a lot more control in the process - minimizing the
chances that you will overbend the bar or slip and hurt yourself.

Ed Bennett

http://www.ts-aligner.com

John D'Errico wrote:

I'm starting to think that I know what happened.

When I withdraw it from the t-track on the saw table,
the front end is captured in the track by a "washer".
This prevents it from lifting during use. But when I
take it off the table to use a different tool (like a
tenoning jig or a panel cutter) I pull it out towards
me.

The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

This feels like the probable cause to me as I think it
over. If so, the solution for the future is simple.
Slide it forward first to release the washer from the
t-slot, then lift it.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?

John

On 22 Nov 2006 09:57:50 -0800, wrote:

Bending the bar back using the "arm strong" method will likely inject
some more stress (you are cold working it). So, don't be too surprised
if it bounces back again. If you can heat the bar up to a dull red
(1000F - 1200F), straighten it, and then let it cool slowly (like in
the furnace) then it should be OK. Or, have a new bar machined from
some hot rolled steel.

Just a little additional, as I've been picking away at forging a set
of spinning tools, and have been researching this a little.

What Ed's talking about is called annealing, if you want to search for
more info on it- it'll bring the steel to it's most malleable state,
and releave the internal stresses. The most common suggestion I found
for the slow cool is to bury it in kitty litter for a few hours once
you get to that dull red color. Bear in mind that doing this will
make the bar quite a bit softer, so you'll need to be extra careful
not to drop it if you do that.

You can get it to that red with a propane torch, but it'll take quite
a while, and you need to keep it moving up and down the bar. There's
also a process for warm-forging that will releave some of the internal
stresses by raising the bar's temperature to anywhere from 150F-700F
while working it (i.e. bending it back into shape.)

Kind of fun to do, actually.

On Thu, 23 Nov 2006 11:52:57 GMT, John D'Errico
wrote:


I'm starting to think that I know what happened.

When I withdraw it from the t-track on the saw table,
the front end is captured in the track by a "washer".
This prevents it from lifting during use. But when I
take it off the table to use a different tool (like a
tenoning jig or a panel cutter) I pull it out towards
me.

The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

That sounds like a winner to me.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?

You can try it, especially if the other option is to buy a new bar- at
the very least, it will release the stresses caused by bending it
flat. If you want to get really involved, find a cheap hibachi grill,
fill it full of charcoal, and set something up to blow air across it,
like a hairdryer or a shop vac.

In article , "Mike Marlow" wrote:

"John D'Errico" wrote in message
...


The gauge itself is moderately heavy - about 11 pounds.
So as I pull it out, I tend to lift a bit as I withdraw
it. Since the end is still captured in the slot, this
means I've been gradually cycling it through hundreds
of small bends over the years, ALL in the same direction.
This is consistent with the direction of the bow.

This feels like the probable cause to me as I think it
over. If so, the solution for the future is simple.
Slide it forward first to release the washer from the
t-slot, then lift it.

Is stress relief with heat an option? I have Mapp gas
or propane. Or do I just buy a new bar?


Stress relief? If you did bend it as you suspect then there is no stress to
relieve. Just bend it back. It's not like you are likely to distort the
steel. You could heat it to bend it back, but you will likely end up
causing more damage to the shape of it than if you just finish bending it
back into shape as you have already done. Heat is a great friend of working
metal, but if you don't know what you are doing or are not careful, that
heat and the associated benefits can turn around on you and all you end up
with is an interesting twist on a theme.

From what I've read John, you're trying to make too much of this problem.
Just bend it back and carry on.


Yes, its true that I may be making too much of it.

I have several goals here. I always like to learn
what I did wrong (if indeed I did put the bend in
it myself by my own methods of work) so that I can
avoid a problem like this in the future. I wanted
to gain some understanding of the mechanism of what
happened. Fixing it myself, if possible, is a goal,
but not a tremendously important one, since I could
simply replace the bar for a nominal cost.

Thanks all for your feedback,
John

I thing we're getting overly complicated here. It's just a 3/4" X 3/8"
X 18 - 24" long steel flat bar, probably mild steel. It's not welded to
anything else or constrained in any way, so there is no significant
stress to relieve. IIRC the OP said it was a 3/8 inch or so gentle
bend along the length of the bar. As long as it doesn't have a bad
kink or tight bend that has deformed it in thickness or width,
just straighten it out by whatever means is convenient, when it slides
freely in the slot it's done.
--
Often wrong, never in doubt.

Larry Wasserman - Baltimore, Maryland -

There are significant stresses. The stress is caused by the rolling process.
For the intended purpose, these stresses can be ignored but, if the bar was
cut, it would act much the same as a piece of "case hardened" lumber. It
would warp.

wrote in message
...
I thing we're getting overly complicated here. It's just a 3/4" X 3/8"
X 18 - 24" long steel flat bar, probably mild steel. It's not welded to
anything else or constrained in any way, so there is no significant
stress to relieve. IIRC the OP said it was a 3/8 inch or so gentle
bend along the length of the bar. As long as it doesn't have a bad
kink or tight bend that has deformed it in thickness or width,
just straighten it out by whatever means is convenient, when it slides
freely in the slot it's done.
--
Often wrong, never in doubt.

Larry Wasserman - Baltimore, Maryland -

On Sun, 26 Nov 2006 21:29:38 -0600, ()
wrote:

I thing we're getting overly complicated here. It's just a 3/4" X 3/8"
X 18 - 24" long steel flat bar, probably mild steel. It's not welded to
anything else or constrained in any way, so there is no significant
stress to relieve. IIRC the OP said it was a 3/8 inch or so gentle
bend along the length of the bar. As long as it doesn't have a bad
kink or tight bend that has deformed it in thickness or width,
just straighten it out by whatever means is convenient, when it slides
freely in the slot it's done.

I agree- but playing with fire can be fun, too. I just chimed in
because the concept happened to fall in line with a recent project.

John D'Errico wrote:
...
I have several goals here. I always like to learn
what I did wrong ... I wanted
to gain some understanding ... Fixing it myself...
....

Admirable goals, all of them. Very much in line with the attitude of
most of us regular RCM'ers.

Do come back, you hear,
Bob

In article ,
Prometheus wrote:
...snipped...
I agree- but playing with fire can be fun, too. I just chimed in
because the concept happened to fall in line with a recent project.

If your name is any indication that must happen pretty often!


--

SDF Public Access UNIX System - http://sdf.lonestar.org