Heat straightening?

Metal Shop
#1

I know enough to know that I need to pay someone that’s a pro to do this:

I have a 100yr old pittman rod to a Treadle sewing machine that is bent. I was hoping someone may know heat straightening well enough to get it visibly straight. It’s steel or iron.

Function - the bearing end connects the Treadle petal to the threaded doughnut bearing that rides on the offset crank shaft.

It doesn’t need to be micro-meter exact, it has some adjustment wiggle room at the top with the threads.

The bent part-
PXL_20210324_150827988~2|690x330!

Machine diagram-
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This is an uncommon pittman arm for an industrial Treadle, and it is close to impossible to find replacements, which is why I want the repair done.

#2

The Arbor press in machine shop would be ideal to straighten that without putting heat to it. It would allow the user to “feel” what force its taking to bend it back.

#3

I worried about it rotating or bending in other spots if I used a press or hammer. I may be over thinking it?

#4

I had good luck straightening the handle of the post vise I restored by heating it in the forge and using the DMS post vise to clamp/straighten it (along with a little percussive maintenance).

#5

A quick Google search shows many Pittman arms were made of wood. As such, I suspect it is mild steel (not a tool steel). If it’s only 100 years old it’s more likely to be steel than wrought iron. An eBay listing for a 1904 wooden Pittman arm mentions that Singer later changed to a steel arm.

With mild steel, you don’t have to worry about ruining the temper when reheating.

As such, I’d recommend the induction forge and the post vise clamping, perhaps with a little tapping on the unheated portions while clamped.

Heat, clamp, unclamp, rotate, clamp. Repeat as needed.

Perhaps someone on @Team_Blacksmithing could help out, as training is required for the use of the induction forge.

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#6

See any reason why this couldn’t be hammered back into shape?

#7

@AmeliaG happy to work with you on this if you would like. I’m familiar with a few methods for accomplishing this.

Thanks

Freddy

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#8

We can always pull out the forge and try. Worst case scenario I can see is you may have to have a new one made. We got the tools to do it and I’m sure if we put enough heads together we can do it

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#9

Hammering on hot metal is likely to dent the surface. The vise can pinch to straighten without dinging up the surface.

Hard cold hammering can introduce stress cracks - tapping the cold parts to persuade the hot parts to move should be ok. It’s not much of a bend, so cold hammering might work ok, too.

I often use the post vise to straighten bends in hot twists without flattening the crisp edges of the steel.

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#10

That should be able to be bent cold. Get a 3’ piece of black iron pipe with an ID big enough to slip most of the way over the bend, clamp the part in a vise, slip the BIP over the bent end, straighten a small section, reclamp and straighten the next section. Rolling it on a welding table once its roughly straight will help you find spots to fine tune.

#11

Failing the ability to repair the one you have, that part is “stupid simple” to machine. You’re looking at cutting it to length, putting threads on either end of the rod, and then making a brass ball to go on the end. From there you’d find a finishing method that makes the surface finish what you want to match what you’ve got.

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#12

I think the threaded end is the difficult part to replace. The ball is 1/2in, and I’ve found 1/4in rod with 1/2in ball already on it online. We’d just have to be sure the finished product was the same length.
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@HankCowdog
This pitman arm is from 1923, I believe wood pitmans went out in 1900 or so. I’ve been wrenching on/studying antique machines for my Covid project, this is my 5th one. But this one just needs more tools & know-how than I have. Y’all’s responses have helped a lot.
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@malcolmputer-
I actually thought I’d be able to get some threaded rod, but I’m told the thread on Singers doesn’t really match with current standard thread sizes, I’d love to get an accurate measure on those threads for sure.
As for finishing, at least that I know! The machines have the same finish as Model T Fords- with an asphalt lacquer, gold decals, and all of it covered with flaked shellac. The bases tend to be just a stupid-thick layer of tinted shellac… and dirt, and grease…
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Method: It seems like several will work to get it ‘good enough’ straight. As long as heating/hammering doesn’t make the finished rod grow or shrink by more than .25 in, or make the part fail, it’ll be fine.

I’ll be fully vaccinated by mid April and I’ll ping then and see who has time to look at it with me?

#14

Looks like a thin (3/8”??) shaft: the induction forge could handle it.

#15

What I’d recommend if you wanted to make it instead of straightening the one you’ve got would be to buy some rod that is the right diameter made out of mild steel, and then you’d measure the threads and set up the lathe in the machine shop to duplicate them.

But that process will be way more complicated than just straightening it, so try that first and if it doesn’t suite you then we can work on training you up on the lathe or farming the job out to someone who is.

#16

Yeah, if it’s working

#17

I know it doesn’t help a whole lot, but here are some ballpark measurements in the pics.
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And for what it’s worth- while Singer COULD produce precision machining (https://www.popularmechanics.com/military/weapons/a23340620/singer-sewing-machine-company-45-pistol-gun/)… they frequently chose not to in favor of profits. There’s a lot of slack/play in most of their machines (the 201 is a notable exception, and it cost 4x what their economy machines cost), and while they’ll take a lot of abuse, ‘Fine German Engineering’ they are not. Which is why I say ‘close enough’ to straight is good enough, and y’all definitely seem to have some ideas for how to get it straight, and some fall backs if it doesn’t work.

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#18

Looks like 1/4-32, or National Extra Fine thread. Uncommon, but not rare. Dies are available, but I don’t expect we have them. But should be able to single point turn If straightening does not work.

#19

@kbraby
Thanks!
You should see the bearing that goes on the end of this pittman. they call it a ‘doughnut bearing’ but no online search I’ve ever done has shown that to be anything like standard. The whole thing has to be assembled on the crankshaft, and the 6 ball bearings ride against the crankshaft itself. It’s got an inner plate, outter plate, and a middle plate with grooves for the 6 bearings to ride against the crankshaft.

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Packed with fresh grease.

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Showing the middle plate.
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Upper plate loosened, the bearings fall out, and the doughnut housing can be slipped off the crank for cleaning/reassembly.

#20

The really GOOD news seeing the photo is: It is made from steel and not cast iron as many of the parts of that vintage were.

Personally, localize heating with the induction forge and straightening in the vise in slow multiple steps as several have recommended will probably give you the best chance is not denting (avoiding stress risers being introduced) or marring the surface preserving original finish. Also, heating is localized or by moving in and out can get a tapering effect for heat affected zone.

Good luck with your restoration!

#21

The thread may be whitworth and 55 deg tooling is hard to find.

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