# How would I know if my spindle is bent?



## MyLilMule (Jan 31, 2021)

My 13” lathe is currently in pieces, but the headstock is still on the bed and connected to the drive motor. 

Before I take the headstock off for rebuilding an painting, what is the proper way to test the spindle to see if it is bent?

I was thinking of getting a test bar from Amazon and a dial indicator to check for runout. But not sure what is should be or how much is too much.

Comments from those that have done this would be appreciated. 


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## Ulma Doctor (Jan 31, 2021)

you can indicate directly on the taper,  or on any projection that is flat.
large needle movements will signify a bent spindle


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## 7milesup (Jan 31, 2021)

What would make you think that your spindle is bent? It would take a significant blow to bend a spindle.


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## markba633csi (Jan 31, 2021)

Also, the spindle would probably not spin freely if it was bent, I think.  Pretty hard to bend a South Bend spindle.  
-Mark


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## SLK001 (Jan 31, 2021)

I don't know how someone could possibly bend a spindle.  They are super hard, so any force strong enough to bend it would probably just snap it in two.  You can't apply force to the pulleys to bend it in the middle, because they are just thin cast iron parts and would shatter to dust before the spindle bends.

The 13" lathe has a propriety taper in the spindle mouth, so your test bar would need to be that taper.  It's been asked, but why do you think that your spindle is bent?


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## aliva (Jan 31, 2021)

Not likely a bent spindle. I you have excessive run  out, check the bearings first.


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## MyLilMule (Jan 31, 2021)

I never claimed I thought it was bent. I want to check it and I want to check it the correct way. FWIW, I have seen others use a 4MT to 3MT adapter with a 3MT test bar in the 13" 1-7/8 spindle (Greg Halligan):






And before anyone asks, it currently has no compound, cross slide, apron, lead screw, gearbox, gear train, chuck or tail stock. Those are all in pieces and various stages of restoration. But before I take the headstock off and apart, I figured now would be the time to check it, and if it needed to be fixed or replaced, fix or replace it.


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## SLK001 (Jan 31, 2021)

MyLilMule said:


> I never claimed I thought it was bent. I want to check it and I want to check it the correct way. FWIW, I have seen others use a 4MT to 3MT adapter with a 3MT test bar in the 13" 1-7/8 spindle (Greg Halligan):



If your lathe is a South Bend lathe of vintage 1941 - 1999, then an MT4 to whatever adapter won't work (properly).  You say the spindle is 1-7/8".  Where?  Thru bore?  The above vintage SB should have a 1-3/8" thru bore and a mouth of 1.628".  So, what lathe do you have?


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## MyLilMule (Jan 31, 2021)

SLK001 said:


> If your lathe is a South Bend lathe of vintage 1941 - 1999, then an MT4 to whatever adapter won't work (properly).  You say the spindle is 1-7/8".  Where?  Thru bore?  The above vintage SB should have a 1-3/8" thru bore and a mouth of 1.628".  So, what lathe do you have?



Ooops. I've had the spindle thread on my mind all day today for another project. It's a 1" spindle bore.

I thought I read it was a 4MT variant, but that a 4MT would fit.


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## SLK001 (Jan 31, 2021)

MyLilMule said:


> Ooops. I've had the spindle thread on my mind all day today for another project. It's a 1" spindle bore.
> 
> I thought I read it was a 4MT variant, but that a 4MT would fit.



The 13" lathe with a 1" bore _*IS*_ bored for an MT#4 taper.  It is the larger bore 13" that has the proprietary taper (0.602"/foot).  A MT#4 may not fit exactly (although, it just might), but the tapers will match, so it will work just fine.  By "not exactly", I mean that it may stick out a couple of thousandths, but it will lock in solid.


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## MyLilMule (Jan 31, 2021)

SLK001 said:


> The 13" lathe with a 1" bore _*IS*_ bored for an MT#4 taper.  It is the larger bore 13" that has the proprietary taper (0.602"/foot).  A MT#4 may not fit exactly (although, it just might), but the tapers will match, so it will work just fine.  By "not exactly", I mean that it may stick out a couple of thousandths, but it will lock in solid.


OK. That makes me feel better and that I wasn't going crazy. 

I'm going to get a test indicator and a dial indicator first so I can check the spindle itself first before looking into a taper adapter and test bar, although those will be on my list of things to get when I start to level the lathe after reassembly.


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