Thread: Regrinding spindle taper on VN 12

"The .0006 runout is measured right on the taper itself, and I have tried many different collets and end mill holders, including newly made Chinese, old VN, shopmade, brand new Hardinge , etc- they pretty much all show the same trend with minor variations - ie the runout may vary from .001-.003 or so, but it is always at the same point in relationship to the spindle. I have removed the key, no difference. "

Another option would be to make a batch of collet's, mount them in the spindle, then bore and ream them. If I were to do this, I would make some to use the ER series collet's. You would loose a little accuracy, but gain a lot more capability in diameters you can hold.

Originally Posted by J_R_Thiele

Another option would be to make a batch of collet's, mount them in the spindle, then bore and ream them. If I were to do this, I would make some to use the ER series collet's. You would loose a little accuracy, but gain a lot more capability in diameters you can hold.

I am going to do this- figure to do all the turning, taper, threading etc in the lathe, then do the final taper bore for the ER on the mill, to get it centered. I have a few VN C taper blanks turned to size, all that is necessary is to cut he ER taper and thread- they are 1144 stressproof steel, probably last me the rest of my life, wear wise.

Bar Z has a YouTube video covering how to do this on a Bridgeport.

Finally bite the bullet and ground the spindle taper today. used a 1/2" diameter stone, 30,000 rpm, spindle spinning at 490.
Brought up the engagement by about .0003" at a time, till the entire spindle was cleanly ground. Then checked the taper, and altered it a tiny bit- .0002" over .375" travel. I don't know what that comes out to be in degrees, but it is sufficient to change a bluing trace. Some of my toolholders are showing a blue trace on the wide part of the taper, and others on the small end of the taper, so that is good enough. Certainly the contact is way better. I wish I had a sine bar and gage blocks!

I was a bit concerned because one forum member had discovered a very thin hardening on his wartime VN12. I thought about for a while and figured even if the hard skin was ground through, it would take the rest of my life for it to be a problem.

So there I am, taper ground, looks perfect, like a new job right out of the factory, I put a ground .500 pin in a Hardinge collet and @#$%*! .0025" runout, worse than when I started! Tried another collet, and end mill holder, all sucked. Stuck a DI on the taper, .0001 runout. What is going on? Finally took a very close look at the pin, and found the end of it, where is it slightly chamfered, had a minute burr all the way around- filed it off with a diamond hone and realized that the job had worked.

The runout with a Hardinge collet is .0003", about 1 inch from the spindle nose. Chinese collet, .0005".

Thank you all for the suggestions,advice, comments etc- I tend to agonize over stuff like this, because of lack of experience and knowing all too well how easy it is to screw up- and on a machine spindle, there is little room for recovery.

stoneaxe, gimme a PM or email the next time you need to use a set of gage blocks.

Congratulations on a fussy job well done with improvised equipment.

I’ve been reading a number of threads concerning spindle runout issues.
This is @ the third or forth thread which found that the pin was causing the problems related to machine runout. Thanks for posting.

Originally Posted by sfriedberg

stoneaxe, gimme a PM or email the next time you need to use a set of gage blocks.

Congratulations on a fussy job well done with improvised equipment.

Thank you!

Originally Posted by tim9lives

I’ve been reading a number of threads concerning spindle runout issues.
This is @ the third or forth thread which found that the pin was causing the problems related to machine runout. Thanks for posting.

The spindle was definitely out, before I ground it- and it still is, depending on what one needs for accuracy- one thing learning about machining has taught me is there is no perfect- there are just limits of measurement.

The pin I used was a simple locating pin, and here is the tricksey bit- since the burr was on the very end, it is possible to slip it in a collet past the engagement surface, and get a good measurement. I don't know how they make these but guess they grind first, then cut them off and some are burred.
A carbide test bar is probably a good thing to have around.

Good job!!!

I felt the dread when that burred up pin gage was giving a 'what the hell' reading. lol



I was tearing into my project lathe's (Andrychow TUG 40) carriage last night. Could not get off the half nut shaft and collar. Spent hours and hours cleaning, looking, tapping, twisting, wiggling, looking for hidden fasteners, hidden access holes and just couldn't figure how that assembly was assembled or how to get it apart.
I don't have a manual.

Finally gave it a good yank and it came apart, it had a raised burr on the shaft/collar interface and that was all that was keeping it locked together.
A 3:30 AM victory in the Battle of the Burrs!

Originally Posted by stoneaxe

one thing learning about machining has taught me is there is no perfect- there are just limits of measurement.

This. And I tell all the high-school students I am mentoring "Everything is made of rubber," including your measuring instruments.