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Shaft Straightening for Old Arn

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Blog entry by papadan posted 05-02-2017 09:25 PM 656 reads 0 times favorited 14 comments Add to Favorites Watch

Was reading the Arnfest thread Here and one of the posters mentioned having a bent shaft in an old drill press. This method doesn’t always work on some of the newer steels and alloys they use nowadays but has always worked on the good old arn shafts and rotors. I actually can’t tell who or where I learned this process, they weren’t supposed to share it with me. I have watched it done and done it myself quite a few times. To start with you need to have small holes in the ends of the shaft, most have these already from the original milling process. You need to mount the shaft between centers on a lathe or set up a couple mounted points to hold the shaft.

When mounting the shaft, do not tighten the centers on the shaft just insert them to support it and allow it to rotate between the centers. Set up a dial caliper and measure the shaft across the length to identify the center point of the bend. Tighten the indicator arms so they will not move and mark the position of the base with a sharpie.

You want to be able to move the indicator out of the way, and put it exactly back where it was. so you can track your progress. With the indicator out of the way start to heat the shaft with an Oxy-acetylene torch. A cutting head will work for smaller shafts but anything larger that about 1” should use a Rosebud heating torch.

You do NOT want to over heat the shaft. All heating must be done on the inside of the bent shaft, not all the way around. Move the torch back and forth over the shaft centering on the bend. You want to get the shaft to just start turning a little red and allow to cool down some. at this point recheck the bend with your indicator. You must keep the shaft loose in the centers so it can move, if it starts to tighten up between centers open them up just a little to allow movement. Do not get the shaft cherry red at all, you will removed the hardness, if using a cutting torch don’t get it too close or hold in one place too long. You want to super heat the whole shaft but not burn or melt any spots on it. When possible, I will perform this process with a camera to show it being done. Keep heating and checking until your shaft is straight.

Remember: Do not over heat, don’t get any part of the shaft bright red, just beginning to turn dark reddish is enough. Keep the heat on the inside of the bend, like the diagram shows. Keep the shaft loose between centers. It doesn’t seem like much but as the shaft straightens it will lengthen. Good luck and Be Careful.

-- Artificial intelligence is no match for natural stupidity!



14 comments so far

View lew's profile

lew

11744 posts in 3505 days


#1 posted 05-02-2017 09:38 PM

Thanks, Dan!

Why does the shaft straighten out? Gravity? Molecular memory?

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View papadan's profile

papadan

3462 posts in 3118 days


#2 posted 05-02-2017 09:46 PM

Lew, it’s molecular memory and you just remined me of something I left out. OK I just fixed it. The heat must be applied to the inside of the bend not the outside. It is molecular Memory that straightens the shaft and that’s why some of the newer cheaper metals wont work with this process.

-- Artificial intelligence is no match for natural stupidity!

View lew's profile

lew

11744 posts in 3505 days


#3 posted 05-03-2017 04:24 AM

Thanks, Dan!

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View TheFridge's profile

TheFridge

7679 posts in 1236 days


#4 posted 05-03-2017 04:38 AM

Stress relieving in a way. makes some sense. Would like to see the vid.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View papadan's profile

papadan

3462 posts in 3118 days


#5 posted 05-03-2017 04:48 AM

Not sure when I will be able to show a video, don’t even have a bent shaft right now. LOL If a person does not have a dial indicator set up they can do this with a good straight edge, just don’t burn your fingers. I have been wondering if this same process would work on a plane iron. Guys are always talking about having to flatten their irons, so maybe this method could work.

-- Artificial intelligence is no match for natural stupidity!

View TheFridge's profile

TheFridge

7679 posts in 1236 days


#6 posted 05-03-2017 04:54 AM

Possibly. I wouldn’t want to re heat treat it myself. I’ve used a block of wood and a hammer. And if that doesn’t work.

I get a bigger hammer :)

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View papadan's profile

papadan

3462 posts in 3118 days


#7 posted 05-03-2017 04:57 AM

You don’t use enough heat to harm the treatment, even if you did heat treating is easy.

-- Artificial intelligence is no match for natural stupidity!

View Rick's profile

Rick

10070 posts in 2130 days


#8 posted 05-03-2017 05:10 AM

Tool steel doesn’t have “memory” in the same sense a plastic that snaps back to it’s original shape when heated. The only mechanism that could move steel in this way would be expansion and contraction. You heat one spot and it expands, bending the spindle, but it would contract as it cooled unless you quenched it and “froze” it in place.

edit; to be honest I thought this was a wive’s tale but I found a video and looks like I nailed the explanation.

https://www.youtube.com/watch?v=dNuSh8ZMKIo

-- http://thewoodknack.blogspot.com/

View papadan's profile

papadan

3462 posts in 3118 days


#9 posted 05-03-2017 05:30 AM

Sorry Rick, I’m not sure about tool steel, my method is for steel shafts from older machinery and motors. Not sure what they are made of but the process does work as described in my blog. This process was invented and perfected by a motor rebuild company a long time ago.

-- Artificial intelligence is no match for natural stupidity!

View papadan's profile

papadan

3462 posts in 3118 days


#10 posted 05-03-2017 05:06 PM

*

-- Artificial intelligence is no match for natural stupidity!

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papadan

3462 posts in 3118 days


#11 posted 05-04-2017 04:12 AM

Just saw your video Rick. Never seen this done with a chuck holing one end or with water cooling. He straightened it enough to put the collar on but his shaft was still way out on the end. I’m surprised I haven’t caught hell from several others on this “wives tale” process, I posted this in hopes of helping some people with the rebuild of old machines and I would never post something like this that I was not personally sure of and have done myself. I haven’t done this in several years now, but Matts post about needing a new shaft for his drill press reminded me of it.

-- Artificial intelligence is no match for natural stupidity!

View Rick's profile

Rick

10070 posts in 2130 days


#12 posted 05-04-2017 05:12 AM

If you have a bent spindle there is nothing to lose by trying. Like doctors say, you can’t kill a dead man. Keith’s shaper spindle was .007” out at the tip (less than the thickness of 2 sheets of copy paper), which by machinist standards is a lot, enough to cause some vibration. I would have heat it one more time but he has a good point that runout where the cutters are will only be a few thou and should be fine on a woodworking machine.

-- http://thewoodknack.blogspot.com/

View TheFridge's profile

TheFridge

7679 posts in 1236 days


#13 posted 05-04-2017 05:19 AM

Awesome process. Good know.

Another tool in the tool box never hurts :)

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View papadan's profile

papadan

3462 posts in 3118 days


#14 posted 05-08-2017 08:59 PM

Just a bump!

-- Artificial intelligence is no match for natural stupidity!

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