Use a dial indicator to center a piece in a 4-jaw chuck?

Nelson

Nelson

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There are a few methods of doing this, so I wanted to get the group's consensus.

What is your way of centering or holding a shape in a 4-jaw chuck?

Photos, of course, would be great.


:tiphat:Nelson
 
i put my dial indicator in my tool post and bring the compound up to my work, i used the small bar that it fits on in the magnetic base to insert in the tool holder:biggrin:
 
In some cases, it's a two stage process, but I use a 1" indicator in most instances. The face must run true first, generally, then the OD or ID (whichever I'm working on). It may take a few switchouts between the face and the OD/ID, but unless I need to reach into a very small area, the 1" indicator will do. If not, I have some extension points for it, or once I get close, I use a test indicator.
 
It all depends on the shape of the piece in the four jaw and what operation needs to be done to it. If it is a square piece (same dimension x & y) then I put a small center point in it and I use a long rod with a point on it chucked up in the tailstock. Then I can put an indicator on the rod and indicate it in to "0" T.I.R.

I also use an indicator on a stem mounted to the compound and will check off the top of the part all four sides until indicated in "0". This method takes a little longer though as you keep having to back out the indicator, rotate the part, then bring the indicator back to the top.

As I said though, there are a few methods, it just depends on the shape of the part itself. If making a part from a blank, then I just eyeball it in a best as possible and cut away everything that doesn't like like the part.
 
Hi Nelson,

Most often I eyeball it central relative to the rings machined int he chuck face, or line up a feature I want centred with the opposite pairs of jaws - this'll usually get it within 2mm / 80 thou", then apply the DTI and rotate the chuck by hand. When the DTI hits the maximum reading I tighten the nearest jaw, working around and tightening as required. If the work won't budge far enough, I rotate to the minimum reading and release the nearest jaw a just touch, turn the chuck 180* and tighten. Repeat until cented / bored :)

If I have to centre a centre-punch mark, I use a centre finder (telescopic rod with a pair of points and internally sprung - a great beginners' project) and indicate that central in the same way with the DTI bearing on it.

Dave H. (the other one)
 
To make sure the part is aligned axially, I put parallels or a spider underneath and tap the part down just like in a mill vise. Paper under the parallels makes them easier to remove. If there is a center punch mark to work from, I'll pick up the mark with the point of a wiggler center finder (Starrett) and indicate that. If there's a hole, I put a gauge pin in it and indicate off that (It's easier than trying to indicate in a hole). If you use parallels, don't forget to take them out before you turn the spindle on! :eek: If the sides of the part are finished, it doesn't hurt to put some paper or cardboard between the jaws and the part so they don't leave marks on the surface.

Actually, I rarely use a 4 jaw chuck because there are usually other ways to hold odd shaped parts that take less time to set up. One way is to leave the part round on the outside to do the lathe work and then square it up afterward. Another option is to bore a hole in the mill on the back of the part and mount it on an expanding arbor.

Tom
 
As Keven, I use a square an old barbaque fork or something chucked in the tailstock with a sharp point into the work.
This way the dial ind. is riding on a flat. This is providing you have center drilled it. Also use two tee handles. Then
if you are to make or face square blocks, it dont matter to be centered just eyeball close.
 
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