How important is lathe chuck run out?

[Pcmaker]

I know it's not an accurate way to measure run out, but I indicated the surface of my 3-jaw chuck and I get around .007 run out.

If I put an end mill in the chuck and indicate about an inch away from the chuck, I get more than that.

How important is chuck run out?

I tried loosening the nuts holding the chuck and moving it around, retighten it, but that didn't do all that much.

Also, if you take out your 3-jaw chuck, is there a process you have to do to get it back on or do you just slap it on there after cleaning the mating surfaces and tighten the nuts?

 

[BaronJ]

Hi Guys,

7 thou is not that bad ! If you want accuracy use a four jaw chuck or a collet.
However if you are going to complete the job with removing it from the three jaw then it probably doesn't matter.

 

[markba633csi]

7 thou is a bit on the high side- my Shars 4" is about 3 thou. If your chuck is mounted to a backplate sometimes you can improve the fit by taking off material and tapping the chuck into position
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[Pcmaker]

Is the backplate where the chuck bolts into? Or is that a separate part from the chuck and where the chuck mates to onto the lathe?

 

[WarrenP]

Thats what I did, I separated the chuck from the backplate on the back of the chuck and took material off the backplate so it could be adjusted more. Then the chuck a bit loose still, tap it on the high side until you get it in position and tighten. I can get mine down to less than a thousand that way, ( I think more if I wanted to cut more off). If you have a piece of round stock you know is actually round (ground , etc) you can put that into the chuck and measure it.

 

[WarrenP]

Is the backplate where the chuck bolts into? Or is that a separate part from the chuck and where the chuck mates to onto the lathe?

I took the back plate off the chuck on mine. If you cut the ridge a little then the outside of the chuck can move more for adjustment. That's how mine was anyway... if you posted a picture with the chuck off everyone could be sure on it.

 

[Dabbler]

I never worried about run-out in my 3 jaw chuck. It is a great practice to plan your work so you can do as much as possible usign a single set up so rechucking is not on the table. In all my time machining, I seldom, if ever had to indicate in a piece of work for a second operation.

 

[RJSakowski]

First, which surface are you referring to? If it is the OD of the chuck body, don't worry about it. If it is the flat face, it would be desirable to have minimal runout as it is useful to use that face as a reference surface. The biggest concern is run out in the jaws. It is ideal to have zero runout in the jaws to permit removing and remounting work as to work on both ends of a part.

I check jaw runout by mounting a dowel pin or similar ground surface in the chuck and measuring the position of the surface as I rotate the chuck. The TIR or total indicated runout is the difference between the minimum and maximum readings. The readings are usually made close to the chuck jaws and at a distance of a coouple of inches from the jaws. The first TIR value is usually considered to be radial runout while the second also includes angular runout. Radial runout is considered to be due to a difference in jaw position due to a poor jaw grind or to wear in the scroll or both. Angular runout is caused by the jaws not being parallel to the spindle axis.

Because of the design of a scrolling chuck, it is difficult to obtain zero runout for all diameters. .003" is not uncommon, even in a new chuck. There is a type of chuck called a "set tru" where the chuck can be centered for zero runout at one particular diameter. Usually, if zero runout is desired, a four jaw chuck is used. A four jaw chuck can correct for radial runout but it will nit eliminate radial runout. Another way is to run your work on centers. This will ensure repeatable zero runout on your workpiece even with removal and reseating from the lathe.

You can work with a chuck with runout. As Dabbler said, try to set up your work sequence so all of critical turning is done in a single setup. This sometimes requires some out of the box thinking. I believe that Joe Pieczynski on YouTube showed a workaround for obtaining zero runout from a chuck with runout.

 

[benmychree]

A sloppy 3 jaw chuck is nearly worthless, you should be able to chuck up a round part and have it run within no more than 3 thou. If it was mine, I'd buy a new chuck.

 

[pacifica]

For several years I used collets and 4-jaw chuck only, then I got a 3 jaw with under 1 thousanths tir and now usually it is all I use, Convenience wins out.