# 3mt In 10k Spindle Runs Out



## spongerich (Nov 4, 2015)

I bought some miscellaneous boxes of tooling at an auction a couple weeks ago and one of the things was a small test bar.  It's 12" long and has 2 1.0000 collars ground on either end.  Since I've never really dialed in the tailstock since I bought the lathe I thought I'd put it on and see how far out I am.   

It'll also give me a chance to see how my setup for turning between centers works since I have a couple of projects that I need to turn on an arbor.

The 10K spindle taper is a proprietary South Bend taper, but I've read that 3MT is close enough.

I have a 3MT to 2MT collar.  I had to mill a slot in it to clear the collet anti-rotation pin but it seems to fit OK.   When I put in a 2MT dead center and indicate it, the best I can get is about .003 which seems like far too much.   I tried with several centers that are all in excellent condition.    Everything has been cleaned 5 times and still no luck.   I know that South Bend made a special 10K spindle to 2MT collar, but even if I manage to find one, it's going to cost a small fortune.

I guess I could make one if I can dig out the dimensions.  I do have a tool post grinder.


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## Bob Korves (Nov 5, 2015)

First, visually look closely at the spindle taper using a good light, looking and feeling for burs and other damage.  Then test the spindle taper for runout.  It will never work if the spindle taper is not accurate.  If that tests OK, then check the bushing (collar) visually for damage and burs, inside and out.  If you find any, stone them gently lengthwise with a fine, flat (and a cylindrical one as well for the bore) oilstone.  You will be able to feel any issues with the oilstone and will also feel when it smooths out as they go away.  Then indicate the bushing bore with it installed in the spindle.  Gently clean up any burs inside of it.  Finally, repeat on the center OD.  Indicate the center on the shank as well as on the point to see if the point was ground off center.  You can use a light coating of Hi-spot blue to test the fit of the center in the bushing and the bushing in the spindle for full and even contact.  A MT reamer can be used to dress the bore of the bushing, but it needs to be used very lightly.  Don't mess with the spindle bore beyond very lightly and gently removing burs unless you really know what you are doing.  Something is not concentric in your setup and it is your job to systematically find it!

It is also possible to mark the high and low spots of the the various parts as you go, looking to cancel out the errors as you add each component.

Edit:  Wait a second.  Anti rotation pin for the collets?  It sounds like you are trying to put a Morse taper center into a collet adapter, probably meant for 3C collets.  The collet adapter has a short steeper taper in the nose, the MT bushing for the center should have only one angle taper for the full length of the bore.


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## DoogieB (Nov 5, 2015)

The spindle taper of a 10K IS 3MT, as a 3MT dead center fits fine.  The thing that screws you up is that a 3MT dead center will stick out to far to use the dog plate effectively with normal drive dogs.  A 2MT dead center with an adapter sleeve is stubbier.

Bob, the 10K uses a 6K collet directly in the spindle, it's not like the 9A with an adapter and 3C collets.  It's unusual to still see the collet pin in the spindle, however, as most of them are sheared-off flush like mine.


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## Bob Korves (Nov 5, 2015)

DoogieB said:


> The spindle taper of a 10K IS 3MT, as a 3MT dead center fits fine.  The thing that screws you up is that a 3MT dead center will stick out to far to use the dog plate effectively with normal drive dogs.  A 2MT dead center with an adapter sleeve is stubbier.
> 
> Bob, the 10K uses a 6K collet directly in the spindle, it's not like the 9A with an adapter and 3C collets.  It's unusual to still see the collet pin in the spindle, however, as most of them are sheared-off flush like mine.


You are saying that the 6K collet is actually a 3MT, that fits directly into the spindle taper?


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## DoogieB (Nov 5, 2015)

Bob Korves said:


> You are saying that the 6K collet is actually a 3MT, that fits directly into the spindle taper?



No, that's not what I'm saying.  There's actually two different tapers at work here: one for the collet and the internal taper (3MT).  While I was searching for drawing of the 10K spindle, I found this little description which sums-it-up better than I can:


> The 10K spindle has a 3MT internal taper as does the 9". The difference is that the 10K has a collet taper for 6K collets built into the spindle as well. The 6K collet was engineered so that it could be built into the 3MT internal taper by adding a short, tapered mouth at the beginning of the spindle taper. There is a key (actually a pin) in this tapered section. The pin passes right through the spindle threads and if slightly ought of place will make the spindle thread look damaged. This is one way to tell a 10K from a 9" Southbend. Since the 6K collet fits directly in the 10K spindle without an adapter, Southbend was able to get a 5/8" collet capacity in virtually the same spindle as the 9" with its 1/2" 3C collet capacity. FYI: a 10K can also use 3C collets if you use the collet attachment from a 9" Southbend (with a 3MT to 3C adapter), though I'm not sure why you would want to do this. 9" and 10K Southbends have a spindle through bore of roughly 7/8".


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## Bob Korves (Nov 5, 2015)

OK, thanks.  I never came across that before.  The pin interferes with the 3MT?


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## DoogieB (Nov 5, 2015)

Bob Korves said:


> OK, thanks. I never came across that before. The pin interferes with the 3MT?



No, it shouldn't interfere, but the pin on my lathe is sheared-flat so I can't be 100% sure.  By the way, I have no problems using collets without the pin with a draw tube as it's easy to stop the collet from turning with your fingers.

Ok, SB specs:

http://www.wswells.com/data/spec_sheet/7324.pdf

I said earlier the 3MT dead center was longer, but apparently i mis-remembered.  I had a few minutes before I had to leave so a ran down to the shop and took some pictures.

This is a 2MT dead center in a SB adapter.  It's showing about .0005 runout, which isn't surprising using an adapter.





And here's a 3MT dead center inserted directly into the spindle.




As you can see, it's SHORTER than the 2MT center in a adapter.  The runout was basically zero on this dial indicator, which is should be better with a direct fit but it's closer to the spindle as well.

So, back to the OP, I think your adapter collar is wonky.   Try a 3MT dead center.


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## Bob Korves (Nov 5, 2015)

The OP said that the collet anti-rotation pin interfered with the bushing and he had to mill the MT2-3 bushing to clear, so it must have been in the way.  The pin may have been replaced, and longer than original.  That milling might also have ruined the concentricity of his bushing, causing the current problem.  Just speculating here...

I am, however, quite familiar with R8 collets and their anti rotation pins in milling machines.  Some swear by the pin, others swear at them.  First, it is a factory standard on R8 machines that they have the pin.  Bridgeport, who designed it, still thinks it is a good enough idea to install in their current machines.  It is no secret, however, that those pins can and do fail when the load on the collet exceeds the friction of the mounting taper.  The pin is not strong enough to stop the rotation.  When it fails, the broken pin can tear up the spindle bore.  So, some people take out the pin, and others have an overload, wimpy tightening, oil, or a crash take out the pin for them.  Perhaps one of those things took yours out as well at some point.  The pin is not strong enough to take all possible loads.  Taking the pin out does not solve any problems either.  If the load is greater than the friction, the collet will still spin in the taper, chowdering the spindle.  It appears that the only real value of the pin is that you don't have to stop the collet from spinning with your fingers when you tighten the collet.  I have had two R8 mills, one with the pin sheared and the other with the pin intact.  The value of the pin as an anti rotation feature is lost by fooling around to line up the pin and the slot.  I have never spun a collet in the taper, because I keep them clean, dry, deburred, and properly tightened, and do not try to exceed the machine's capabilities.  Which is not to say that it cannot happen to me, just less likely.  Most of the time having the pin or not is not really a conscious choice -- it is either gone because it broke off or in place because taking it out entails removing the spindle...


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## DoogieB (Nov 5, 2015)

Well, all bushings aren't the same and the factory one isn't very long.  Perhaps that was the OP's interference problem.

Here's a thread on how to replace the collet pin.  It has decent pictures of the spindle.

http://www.practicalmachinist.com/v...10k-spindle-6k-collet-pin-replacement-245622/

See on the first picture where the pin is?  It's easy to hit when inserting stock from the chuck side.  Or perhaps the original owners of my lathe decided to file it flush for that reason.


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## spongerich (Nov 6, 2015)

Thanks all...  The pin on mine definitely interferes with the MT sleeve.   I'm half tempted to just try and remove it.   
Before I do, I'll dig up a 3MT center and see if that runs any better.   I do think that the bushing is to blame.  I used several different good centers and all of them wobbled like crazy.   It's possible that despite being pretty careful, I squashed it just a little when I was cutting the slot.


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