Trueing Spindle Bore

[Tozguy]

Ever since I discovered that the spindle bore on my lathe is eccentric I can't sleep.
I want to turn it true but was wondering if it might change the stress in the spindle and warp it (or produce some other unwanted result).
Leaving it alone is not an option unless the guys in white coats get me first.

 

[Tony Wells]

Likely as hard as a landlord's heart.....so you probably need a grinder. If is a small machine, that would be most difficult. Best learn to live with it, I think.

 

[Tozguy]

Tony, haven't had a landlord in a long time. The current boss around here has a kind heart so maybe there's a chance.
Seriously, I managed to drill and tap the outboard end of the spindle with no issues. If worse comes to worse it will cost me a $2 brazed carbide tool to find out the hard way.
My main concern is about how the spindle will like having some metal removed from one side only.

 

[Tony Wells]

I would suspect that like most heat treated hollow rounds, it will move some. Whether enough to cause problems is a guess. But if it's that small, boring the full length of it may be problematic.

 

[Tozguy]

The bore is 1.490'' in diameter. From the spindle nose to the other end it measures 14.5'' long. I am making a boring set up with a 1.25'' dia. bar that is 36'' long. You are right, it remains to be seen if I can get things ridgid enough to bore all the way through.

 

[dfletch]

Wait a minute! Most spindle bores I'm familiar with have a taper for the first few inches for holding centers, collet holders, etc. Why bore it all the way through?

 

[Dan_S]

I don't want this to come off the wrong way, but why do you think it needs to be perfectly concentric? also how much is it off by?

 

[Tozguy]

Fletch, you are right, there is a MT5 taper for the first 5 inches in from the spindle nose. The spindle bore starts to be restricted at the 5.5'' mark. The MT5 taper is concentric to the spindle axis so it won't get cut.
After that the bore is 1.490'' but not concentric with the spindle axis, by how much is a good question, maybe in the neighbourhood of .025''.
Dan, you are right too, for a normal person this is a perfect case of 'if it ain't broke don't fix'.
But I have a few ideas about how to go about boring the spindle that I am itching to try. Wish me luck, it might take a boatload of it to pull this off.

 

[Brain Coral]

Hello Toz

To each his own, but why on earth would it be necessary for the spindle bore to be perfectly concentric? It's job is merely to allow work, of up to a certain size, to pass through the headstock and present itself to the chuck. I am quite certain, that if you go ahead with the boring procedure, you will alter the spindle enough to render the bearing surfaces out of line with the spindle.

You seem determined to go through with it, so.... good luck.... by the boatload....

Brian

 

[Tozguy]

Here is a pic of the shoulder beyond the MT5 taper. The taper is covered with a plastic sleeve to protect it when not in use. You can see how far off the bore is to the concentric section.


Brian, you may be right, I will look a bit further into the possible side effects. I am sure others have gone before me so maybe I can turn up some evidence one way or another.