Tight jaws on Burnerd chuck

I recently got a S/H 4 jaw independent chuck on eBay. It was only £50+, & the only wording on it is 'The Burnerd made in England'. Diam. is 4.5"& it runs perfectly on the ML10 & has no signs of abuse or wear. The screws for the jaws are not captive. The problem is that even after some 10 hours work, I have only managed to make one jaw move to my satisfaction. The remainder start OK, but about half way into the travel they start to seize up. All jaws & screws have been removed & files, diamond files & coarse grinding paste don't seem to solve the problem. Sometimes I remove the screws & work jaws by hand to bed them in, but on replacing jaws & screws,I'm getting tight spots & then near the end of the travel, they are jamming up. Am I expecting too much from an (approx 50 yr old chuck)?. I have a 3 jaw PB bought from new with the lathe( S/C), which is as good as when purchased 30 yrs ago.

Any advice welcome,

Mike.

Think I'd be giving everything a VERY good clean before starting work with any tools that could remove metal.

Once it's all spotless then reassemble and identify any tight spots and look for burrs or embedded swarf etc. A chuck of Bernerd quality would have been right when new and is only likely to wear and get a bit looser with age, apart from muck and swarf getting in.

With a 4 jaw independent, provided that there isn't too much play that stops the jaws seating on the work squarely I can't see any reason why pure age should enter into it's usability, it hasn't got scrolls or gears that will wear. If the jaw screws are not on the point of stripping they should still tighten up OK.

Mike Have you tried the screws on their own

Roy

Michael,

Perhaps a silly question, but the jaws are the ones that belong with the chuck? And in the correct slots

Have you also tried them the other way round?

Brian

Try the jaws and screws separately, make sure the jaws are in the correct slots, they should slide without binding. Try the screws, if they start OK but start binding when you get past the groove which engages the jaw they may be twisted. If you need to replace the screws buy some 1/2" X 1" BSW grub screws and cut a groove. You will need to make a Hex key to suit.

Dave

Jaws are in the correct slots, & each is marked with same number, but I've no way of telling that these are the jaws that belong to the chuck as there is no ref. number on the chuck body.

Jaws & screws are, of course hardened, but chuck body is not. There are 10 mating surfaces between each jaw & chuck body, so 40 closely machined surfaces have to match to close tolerances. Jaws & screws have been tried separately -sometimes I can slide jaws to & fro without much effort, & if screws are removed these will also tighten up about 3/4 of the way. Jaws have been tried both ways around with similar results.

Finally, there is no evidence of swarf, & everything has been given a good brushing out with a stiff, new round glue brush & plenty of WD40.

Thanks for all comments & suggestions - I'll just keep persevering.

Mike.

I have a similar Burnerd chuck. The key holes in the screws were split due to abuse in its previous place of work

I bought the longest socket head grub screws I could find, and machined grooves in them as described above,

FOR several years I used a Tee handled Allen key, until the plastic handle fell off. Imachine a steel handle and welded the Allen key into it. It feels good and is good.

The jaws are all the same, and a thorough clean should help. Then juggle the jaws one after the others to get asmooth assembly.

Ivan

Well, you learn something every day; in fact two things today, so I can take it easy tomorrow. I'd always assumed that independent 4-jaw chucks didn't bother numbering the jaws as they are nominally all the same. But there it is on my 4-jaw, numbers on the body and the jaws.

In my experience when swarf gets trapped in a chuck mechanism a brush and WD 40 isn't going to move it, more like a metal spike and soft blow hammer.

Andrew

If you can remove each jaw and its respective screw then place the screw on the toothed jaw surface, you should get a feel for if the threads match. Replacement new jaws for Pratt Burnerd chucks are intended to be "fitted" because the jaws are made assuming there is going to be slight wear on the chuck body so that may be the cause of the tightness.