Worn Myford 4 jaw

I was given a small Pratt Burnered 4 jaw chuck for use on my ML10, It is approximately 3.5" diameter

When I cam to use it, I found that all 4 jaws lifted to varying extent as I tightened it up on a square bar.

Looking at it carefully, the wear was in the plane at right angles to the chuck surface. One jaw could be rocked to an alarming extent and two were not all that bad the fourth was almost acceptable.

Where is the wear likely to be, on the jaws themselves(i.e. in the grooves) or is it mainly in the chuck body? I have yet to measure the slots in the jaws. I can probably use some slip gauges and feeler gauges in combination to measure the slots , measuring the chuck body is a damn sight more awkward!

Is the chuck scrap or can the fault be rectified? Indeed is it worthwhile doing? It is a neat little chuck and if they were still made, I would buy another. Very useful for small delicate work.

Andrew.

I've just thrown away a Burnerd 5" 4-jaw for the same reason. The body itself was the worn bit, as the jaws are a lovely fit in my newer 4-jaw. I kept the jaws as spares. So assuming yours has suffered the same wear, I don't think there's a lot you can do to recover it, short of machining up a chunk of cast iron to make a new body! (In that respect, I think the major difficulty would be forming the screw threads into it.) It may be possible to machine away the existing grooves and let in some chunks of material, but the effort involved would be immense.

Unless you like doing that sort of thing, I suspect your only solution is to buy a new chuck. I got one from Ketan at Arc Euro (the Zither Indian ones) and it's very good for the price.

Before buying, I'd had a look at a lot of the Chinese ones sold by Warco, Arc and others, and the problem with them is the stupid chamfers they put on the front inside corners of the jaws. You can't grip anything thin with them.

Hello Andrew,

​I think the wear is mostly likely to be the guides in the chuck body that slide in the jaw grooves. The bodies were simply cast iron, the jaws are in hardened steel.

​I am not hopeful that you can salvage the chuck, it might be easier altogether to find another one and fit it to your back plate. You can then salvage jaw screws and the jaws as spares for the replacement. if they are ever needed.

Regards
Brian

Don't scrap the chuck body ... think of it as a tee-slotted faceplate.

MichaelG.

Hello Michael,

Now that is a good idea, at least I can use it for something! It is a pity about the chuck as it is built for the Myford, that is to say there isn't a back plate, the threaded nose is integral with the chuck body.

I may as well take it apart and learn a little as to how the chuck was designed. After that I can put it all back together and make up the fittings required for face plate work!

Andrew,