Toolmex chuck problem?

The Toolmex chuck that came with my Myford, is visibly off centre when running. The outside of the chuck wobbles!

Checking with a DTI, the outside of the chuck had a run out of around 25 thou! I casually checked the run out of a 1" steel rod at the chuck jaws and the run out was 2 thou! An 11mm silver steel rod had 1 thou run out! This was a totally unexpected result and I am glad I checked, as I was about to unbolt the back plate and remedy the 25 thou run out of the chuck body!

I have never seen anything like this before. The back .plate thread and the mandrel nose were clean and the jaws are in the correct order. How the previous owner managed to get the chuck running so well is a mystery to me.

Any thoughts on this intriguing situation?

Andrew.

If the register in the back of the chuck is true to the jaws it should be no problem for anyone to get it to hold true

Just a thought, but are the jaws inserted in the right order?

It might be that the previous owner did their best to correct for the asymmetry that would create?

Jon

Hello Jon,

The first thing I checked was that the jaws were in the correct order, I did say that in the post.

Jason. I would normally turn up the back plate to fit the register of the chuck. This I assume is what the previous owner had done. If the chuck runs true then fine, what bothers me is that the chuck register is not concentric with the outer chuck body. I see where you are coming from. But the point I am making is that I have never seen this mismatch with outer chuck body and its register.

I don't know how chucks are made, but I can hardly believe 25 thou run out on the outer body. Maybe the register is concentric with the outer and then the previous owner would have had to enlarge the bolt holes and turn down the back plate register to allow movement of the chuck, to get it running with the jaws concentric. Hence my comment about the possible difficulties that the previous owner might have had.

Andrew.

Sorry, missed that

Hi Andrew,

Is it possible the previous owner ground the jaws true after mounting the chuck?

If you have another set of jaws you can try them to see if they run true.

Keith

Andrew - have you actually checked the register on the backplate for concentricity and diameter, and also checked the register in the back of the chuck for the same. Unless you do, anything you think may be happening from the front view will be just a guess.

You need to go from first principles.

Hello Keith,

You are absolutely correct in what you say. I would check out the back plate. However IF the previous owner had turned the back plate register down and enlarged the bolt holts to get the chuck aligned, then I am blowed if I am going to disturb the present set up!

What can be said without any doubt, is that the jaws are aligned to the lathe centreline within a thou or two (Which is good enough for me, as the chuck isn't my best one!). However the chuck outer body is NOT concentric to the centreline, having a run out of 25 thou. The best explanation is that of Keith Rodgers and that the jaws have been ground true. The outside jaws look as though they have never been used (still wrapped in anti rust brown paper!). If anything they are a touch more accurate than the normal jaws, the run out on various chucked pieces of rod is just over a thou.

I suppose I should just forget the pronounced wobble and get on with the turning. The trouble is that any of my friends that see the lathe at work say "I should fix that dreadful run out!". I am almost tempted to try and turn down the offending chuck body!!

Andrew.