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Suggestion on Straightening Shaft After Hardening

markz528

Hot Rolled
Joined
Sep 25, 2012
Location
Cincinnati
Trying to help someone with a shaft straightening issue. He is now making the shafts shown in the picture below, and is having a very hard time finding a competent/affordable source to straighten the shafts after hardening. Shaft diameter is roughly 1.5 inches. Made out of 4340 or 4340M (he makes both). Hardness target is 40 - 45 RC. They are bowing up to around 0.030" after hardening. He has tried about 6 different outfits and has not had good luck with any of them. He does have one vendor that can straighten them but its a long shipping distance and he is trying to avoid that. These shafts also need to stay affordable, crazy prices just to straighten will just not work. In 2020, these shafts were selling for $900.

Metallurgist says stay under 800 deg F to not affect hardening/tempering. Plan to run some trials on bad shafts, but not even sure if they will straighten below 800 deg F. These shafts have low ductility and therefore cold straightening is not an option - one shop tried it and it broke in half.

I think the plan is to do them in-house if can figure out the process. I have a crazy idea how to semi-automate the process if we can figure out how to successfully straighten them with heat. But the major obstacle is to figure out how to do it with heat. We have a good understanding of the basic concepts of straightening shafts with heat - I have been involved with straightening several large shafts, so these small ones are a different animal for me - and different material.

Any suggestions?

IMG_5317.JPG
 
These shafts have low ductility and therefore cold straightening is not an option - one shop tried it and it broke in half.
That's a definite bunch of hooey. You just said 4340 and 300M. Those are two of the most ductile steels in common use.

For a few parts a month, you get a harbor freight hydraulic press and a pair of v-blocks and an indicator. For more,




This is how people have successfully straightened heat-treated steel for the past several hundred years.
 
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You can minimize the warpage by hanging the shafts during heat treat. This may be happening already because. 030 is not that bad.

Somebody is doing something drastically wrong if they broke a HRc 45 shaft. If you are talking about using heat to spot straighten it that will be way over 800*.

Emgo mentions Mae-Eitel which makes great stuff but it is $$$$$. I have a 16 ton eitel press but it may not have enough poop. They do work great and quick. Undoubtably the best way. You can get a shaft very close in short order

Peening will do it but it can be ugly. Emgo is right about the press and vblocks but it is really tedious and slow. If you have many to do it is brutal and some guys just can't get the hang of it.
 
You can minimize the warpage by hanging the shafts during heat treat. This may be happening already because. 030 is not that bad.

Somebody is doing something drastically wrong if they broke a HRc 45 shaft. If you are talking about using heat to spot straighten it that will be way over 800*.

Emgo mentions Mae-Eitel which makes great stuff but it is $$$$$. I have a 16 ton eitel press but it may not have enough poop. They do work great and quick. Undoubtably the best way. You can get a shaft very close in short order

Peening will do it but it can be ugly. Emgo is right about the press and vblocks but it is really tedious and slow. If you have many to do it is brutal and some guys just can't get the hang of it.

I had an 8620 shaft that I wanted heat treated vertically, it was shorter then the OP's shaft and most HT'rs around here (LA and OC) couldn't hang the part because they didn't have quenching baths deep enough. Except Certified HT

That surprised me, probably a result of the consolidation going on around here with HT facilities.

Certified as well as most all HT'rs around here will straighten shafts. How close they get it is anybodies guess.
 
That surprised me, probably a result of the consolidation going on around here with HT facilities.

IMG_2575.jpg

That water sure is cold !

Deep, too :)

Certified as well as most all HT'rs around here will straighten shafts. How close they get it is anybodies guess.
Hanging vertically does seem to help but it's not the Magic Answer. Still have to straighten usually. Edwards used to do a great job, got them within a few thousandths, but like you say, "consolidation". I believe he's renting the building to a marijuana growing operation now.

(My dog is famouser than me, they were still asking about her ten years after I moved ...)
 
Hanging vertically does seem to help but it's not the Magic Answer. Still have to straighten usually. Edwards used to do a great job, got them within a few thousandths, but like you say, "consolidation". I believe he's renting the building to a marijuana growing operation now.

I was concerned as the shaft had a few changes in cross section and I left .005" on the diameter to clean up. The grinder wanted .010" on the diameter. It was ground at Electro Chrome so they could have chromed and reground if it didn't cleanup, so I didn't lose much sleep

Around Compton a few shops I knew didn't renew their leases because they jumped more per/ft^2 then they could afford. All because the leesees knew they could get more from the grow operations. And apparently the grow ops aren't doing well due to over capacity.
 
Question to the OP...how straight is straight enough? If that shaft is 1.5" in dia, it could easily be 3ft long based upon the photo.

Is changing the material not an option? Maybe to an air-hardening steel?
 
I'd be very surprised if a 4340 shaft at 40-45Rc snapped during straightening. Something is off if that happened. Like there was already a crack.

Anyway. I'd cold straighten in a hydraulic press if I were doing it. You could just as easily straighten with a torch, but the person doing it needs to *know* what they are doing or you'll end up with a hot mess... :D
 
How about:-
If the hardening is for wear resistance, rather than higher tensile strength, use 4340PH and get them gas nitrided after machining. Temperatures involved are less than the temper temperature and won't cause additional bending.
 
could make a jig that holds both ends with a "pusher" in the center and a dial indicator on the opposite side. You could screw the pusher in and bend the shaft and use the dial indicator to see how far you had to bend it to fall within the required tolerance.

Or like others said, just use a press or machine after heat treat
 








 
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