[How do I?] Restore Morse taper in lathe spindle

gasengin

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I have a 10 by 36 Atlas lathe with a MT#3 in the spindle. This lathe was well used. It looks like a collet may have spun in the spindle. The collet has about .005 run out. The bore is not as smooth as it should, but I don't feel any burs that would account for the run out. The outer diameter of the spindle is about 1/2 thousandth out so not likely any other issue. What is the best way to true it up? I need some guidance on this as it needs to be done correctly. Thanks

PS. I checked my 9 by 18 Logan and it was about 1/2 thousandth both on the collet and outer diameter of spindle.
 
It can be cut using the compound rest, holding a tool post grinder or similar. The grinding wheel must be at exact center height, diamond dressed in the setup, and the compound rest must be set to the exact correct angle (actually half angle) of the MT3 taper. While grinding, the spindle should turn fairly slowly in the reverse direction than the grinder wheel. This job needs a fussy and precise setup to be useful when done. The use of a sine bar and gage blocks (or an adjustable parallel set to size with a good micrometer) works well to set the compound angle, the degree scale on the lathe is useless for the required accuracy.
 
I have no experience on this repair, nor have I done any research.
Should bearings/bushings be replaced first then everything leveled in plane then grind as you suggest?
Or, would it be better to remove the spindle and have it ground on a cylindrical grinder.

This question appears in medicine all the time.
The physical therapist might attempt to correct how a patient walks in order to improve spinal alignment.
Whereas a spinal surgeon corrects the spine to correct how a patient walks.

Please understand that the above simplification parallels how a medic understands the dynamic discussions which PT, OT, Chiropractor, Orthopedists, and Surgeons, etc might have. I've had the opportunity to listen to these debates/controversy.

Daryl
MN
 
Hi Daryl,
in a perfect world,
the bearings and bushings should all be replaced prior to the final runout being indicated as well as having the spindle worked in a more precise machine than the lathe itself.
the headstock would then be assembled, set to preload and then to final clearance.
you could then indicate the spindle taper, knowing that the taper is true (or truer than it ever was)
longitudinal adjustment would be made by the headstock alignment
 
My 2c,
Check the bearings if O.K. grind until smooth. Should need very little taken off to true and remove spin damage. Does not need to be 100% mirror polished. An example, on a brand new lathe,(MT6), spindle taper contact bands were at rear and front of taper with a relief in the center of the taper. Contact was not even all around the circumferance but a 10 minute lap with Colgate Ultra White made it perfect although with a satin finish.
The object is to end up with a taper true to the axis and enough contact to hold well. If your chucks and the chuck mounting surfaces are true to the axis correct the internal taper.
It is also an excuse to build some sort of toolpost grinder if you don't already have one aye?
 
There are grinding shops out there that will take your spindle and regrind the taper for you. It is not cheap, but the end results are a nicely ground tapered bore to your needs.
 
FYI, the easier way of making a decent Morse taper in a lathe is to mount a known good one ( a good quality new one, preferably) in the spindle and indicate it with a .0001" reading DTI mounted on the compound slide until the needle stops moving as you traverse along the known good one using the compound crank. In your case, with a known bad spindle taper, that is not an option.
 
Thanks for the replies. The out side diameter of the spindle runs within 1/2 thousands (which is about the same as my Logan), so I believe the problem is in the taper bore. The lathe is an inexpensive Atlas, has been well used, and has wear in the bed, so spending much money on it cannot be justified. The more accurate the better, but how well can the rest of the lathe hold that accuracy? Looks like I have some meticulous step work to do.
 
@gasengin

First, Welcome to the Hobby-Machinist!
As you have already seen above we have many knowledgable people that are great at sharing that knowledge.

Second, if it were me, before I jumped to regrinding, I'd look again real close. It may be difficult to feel a small burr.
I'd find a "like new" taper that fits, blue it, then gently engage it to the spindle and twist it by hand.
With a good flash-light down the other end of the hollow spindle peek in and see if you can locate one spot that's blue.
(unplug the lathe and remove any centres from the tailstock first!)

If that finds nothing I might try it a couple times, and even try reversing it.....blue the spindle bore and look for shiny spots on it after inserting the clean morse taper. It is all fairly cheap insurance.

Also, if the spindle is not hardened then you might try a Morse taper reamer. It would clean up any burrs quickly as long as there's enough socket there to guide it in straight.

-brino
 
Amother 2cents worth,
As above, that should have been the first step. If the spindle has been damaged by spinning it was most likely due to have an arbor fitted without retention i.e. a drawbar through the spindle.
You have stated the lathe is old and worn, it can still be set up to work well and problems slowly worked through. A first step would be to level. I have 2 expensive levels but this method:
is cheap easy and very accurate.
After this apply 'Rollie's Dad's Method' to check headstock and bed alignment.
Align tailstock to headstock.
If you find you need to grind internal taper hold a piece of scrap in the chuck. Turn a 60 degree taper on it, fit a center to the tailstock and hold a new or good condition arbor with the correct taper between the two centers as per Bob Korves. Set you compoud to this,(taper), surface, fit your newly made/cobbled together toolpost grinder, true wheel and proceed to make very light cuts checking frequently with your good arbor and dye.
Don't rush and double check every step. Make notes as you go and you will end up with a good lathe that you can take pride in.
 

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