Paul

they are easy to take to bits but you need a press or large vice and spacers to push the body ring off..having said that i have one that does what you describe and i cant see anything wrong with it inside..

I would also tend to suspect a cracked outer ring, the interferance fit should be enough to prevent the tightening forces causing slippage.

Fair enough, it just looked like the shank of the cutter was shiny then marred exactly where the chuck Jaws are, like it had been slipping, good to know you know better.

The ring pushes off over the printing, back off the jaws underflush before pressing. There are marks on the jaws to help when refitting them in the correct order like the jaws in a scroll chuck.

Edited By old mart on 01/02/2021 18:10:09

And run a file or stone around the snout to knock off any high spots before pushing it into the ring. Sometimes there are burrs there, especially around the three keyholes.

When you disassemble it, the nut will be in two pieces and look as if it is broken. It is made that way: in one piece with weak points and then split to facilitate assembly.

If you cannot find any visible cracks, and do not want to proceed straight to disassembly, make up a clamping collar to go around the ring, squeeze it up tight and see if the wheelspin disappears.

Possibly, you could repair it by drilling and tapping the outer ring for grubscrews. Rather than exerting pressure on the nut, which might not be a good idea, you might have to grind a dimple in the nut just so the grubscrew stops relative rotation of the two parts.

I would be inclined to try a somewhat nasty fudge to restore the necessary interference between the split ring and the outer ring. Find some 2 thou (or thereby) brass shim and make packing pieces to insert in the splits. Brass would be more able to conform to the irregular split line and bed to a uniform spacing, and if necessary, anneal it.

Putting 2 thou in both splits would result in circa 1.3 thou increase in diameter, so quite a tight interference. You would probably need to glue the slivers of shim in place for assembly, but once pressed together it would be solid.

The current Jacobs chucks are made in China and are not reconed to be of the same standard as the UK, or USA products. I have been lucky and have picked up a NOS 1/2" British made one. The best running chuck we have at the museum is an R8 integral shank 1/2" Cutwell keyless one. You may be lucky buying a cheap chuck, they all seem to vary in runout, even the expensive ones. My favourites are the Kawasaki keyless, they will run in reverse if needed.

Edited By old mart on 03/02/2021 12:16:17

I've got a couple of Jacobs chucks that are a bit 'sticky' in places so I think I'll have a go at fixing them. It won't be a big loss to me if they are scrap as I got most of them 'free' when buying other stuff (the box of junk that often goes with used machinery)

There's several good video's on youtube this being one of them link another worth a watch is by mr pete 222

H