Author Topic: Bent shaft  (Read 1096 times)

Offline John Rudd

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Bent shaft
« on: August 07, 2020, 11:35:59 AM »
Another posing question to the collective minds

I have a steel shaft of 5/16" in diameter, one end has a set of gear teeth cut, the other fits in a pb bush...
The shaft is bent! ( where exactly I need to determine) but I need the scetion with the gear....

If I can cut it, so that the bent section can be thrown away and a new section 'grafted' into place....

What is the best way of doing this?

Assuming it can be done.....

Ideally I could do with a new shaft, but I cant cut the helical teeth... 😢
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Online Pete.

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Re: Bent shaft
« Reply #1 on: August 07, 2020, 11:53:09 AM »
Chuck the end of the shaft in a collet and run the lathe slowly. Put a dial gauge on the shaft mounted on the carriage and move the dial away from the chuck until you see it start to swing. That's the start of your bend.
Now repeat it by putting the helical gear in the chuck. When the needle start to swing - that's the end of your bend. Mark both ends of the bend and then you can set about straightening it.

Offline AdeV

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Re: Bent shaft
« Reply #2 on: August 07, 2020, 12:13:07 PM »
Mark both ends of the bend and then you can set about straightening it.

You can also figure out exactly which way it's bending (so long as it's a simple bend, and doesn't have twist as well) - the highest reading will be when the bend is exactly horizontal and towards you.
Cheers!
Ade.
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Offline Sea.dog

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Re: Bent shaft
« Reply #3 on: August 08, 2020, 04:10:17 AM »
Once you've identified the start and finishing points, chuck the part with the start held in a collet. Do you have a lathe centreing tool? (http://www.clickspringprojects.com/bump-lathe-centering-tool.html) If not, you need one. I've used this method before, fairly successfully to strighten the odd small diameter piece.

Online awemawson

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Re: Bent shaft
« Reply #4 on: August 08, 2020, 04:33:48 AM »
Sounds like an armature shaft to me  :scratch:

It is possible to 'cut and shut' armature shafts - in fact the motor on my Bridgeport has just that as when I got it's motor someone had sawn the working end off the shaft! I had the sawn off bit, so I mounted it and the shaft  in a collet, drilled and bored a suitable axial hole, then also a radial cross hole for pinning and assembled it with Loctite.

It's now been running for over 20 years so I reckon that the temporary fix can be regarded as satisfactory  :lol:
Andrew Mawson
East Sussex

Offline John Rudd

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Re: Bent shaft
« Reply #5 on: August 08, 2020, 05:42:24 AM »
I was thinking, chamfer at 45 degrees, drill both ends, insert suitable joining piece and weld up..Then machine weld to finish dia...
Yup, Andrew tis my armature shaft... :lol:
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Online awemawson

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Re: Bent shaft
« Reply #6 on: August 08, 2020, 07:44:00 AM »
Concentricity is your problem welding. It might be absolutely fine when you set it up, but it won't be when it cools.

I think I had sufficient length spare to make a male & female thread meeting conically. Or I might have drilled and tapped both ends female and run a stud between them - don't remember. I do remember debating long and hard over the cross pin - stops unscrewing but makes a weak point. Anyway I did and it hasn't broken (famous last words!)

Andrew Mawson
East Sussex

Offline mattinker

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Re: Bent shaft
« Reply #7 on: August 08, 2020, 08:09:10 AM »
This is only 5/16 shaft, why not try straightening it?

Offline John Rudd

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Re: Bent shaft
« Reply #8 on: August 08, 2020, 08:44:36 AM »
Think I'm going to have to strip the armature and remove the stack, down to the bare shaft and see how it is... :scratch:
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Offline mattinker

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Re: Bent shaft
« Reply #9 on: August 08, 2020, 09:46:03 AM »
John,

Do you have a way to set it up on V or other blocks to find out exactly where it's bent, you might find it's bent next to a bearing seat. It might well be possible to straighten it without stripping it!

Cheers, Matthew