Chuck woe solved

[kenrinc]

Just wanted to thank everyone who gave me input on fixing my new 5" Bison chuck that wouldn't turn concentric. I haven't solved WHY it turns .005" off. I screwed on an old faceplate and it too spun .005" off. The spindle threads are so clean you can eat off them and can't feel any burrs. Anyway, on the Bison, I ended up separating the backplate from the chuck, shaving off .010 or so where the chuck registers with the backplate, remounted it, snugged up the bolts and then just indicated and tapped down the highspots till I got it within .0005" (about what the spindle runout is).

So I'm happy !

Don't worry I'll have more question for you later in the week..... :-)

Ken

[Evan]

Ken,

It sounds like you did the right thing.

When you buy a chuck with a backplate you must first remove the chuck from the back plate. Then, you spin it on or lock it on according to your spindle mounting. Then you face it off as accurately as possible. Then mount the chuck.

I have been following these threads and this evening decided to measure the runout of my 5" very early Bison that I bought a little over twenty years ago. I have used it often. It has done many an interrupted cut, been loaded to the max. But, I have never abused it.

I used a couple of pieces of stock to measure it. One, a piece of 1 1/4" precision ground round bar. It measured .002 TIR at the chuck. The other was a piece of 3/4" round optical rail of hard anodized aluminum. It also measured .002 TIR at the chuck. Then I extended it six inches from the chuck and it measured .0035 runout six inches from the chuck using two different indicators.

I did this with no special care. The chuck was spun on a week ago for a different job with my usual lack of attention.

Realize that the chuck runout (on the outside diameter) does not represent the runout of the jaws on a three jaw chuck. You may expect .003 or so.




[This message has been edited by Evan (edited 01-09-2005).]

[Evan]

On the issue of concentricity. As an example, the tap holder I made recently is an example of how concentricity matters and doesn't matter. I want the tap to be concentric with the axis of the drill chuck used to hold the power tap. I couldn't care less if the outside diameter of the tap holder is concentric with the tap. So, I chuck up a bit of bar stock in the three jaw and drill a hole through it that is the right size to hold the tap, with set screw. I then drill a slightly larger hole in one end that allows a press fit of the cheap off the shelf screwdriver bit that I pressed into the hole. The tap holder end is concentric with the screwdriver bit end. That is all that matters. It doesn't matter a whit if the outside diameter of the holder wobbles a few thou in operation.