Soft Jaw Boring Issue

I went to bore some soft jaws today and had an issue that currently has me stumped. I need to bore full depth for bar stock to pass through, so cannot use a stepped plug or whatever to the rear of the jaws, so reach for my Jaw Ring (see picture).

Now I've used this satisfactorily before, but today, adjusting it to space the jaws approximately where I want them under compression, the chuck closing force just moves the sliding pegs down the cam shaped grooves reverting to chuck closed. Obviously there is insufficient friction between the sliding pegs and the cam grooves. So experimenting I switched the chuck to low clamping force - same happens - argh !! Then I reduced the hydraulic pressure for 'low clamp' as low as I could and still same symptoms. (second argh !!! )

Now I can make up a plate with three pegs welded on in about the right place with a central hole for my boring bar, but why is this suddenly happening. How can I increase the friction in the slots to stop the pegs sliding round back to closed ???

Anyone else had this issue?

Weird. I use that same gizmo to set my soft jaws, but the pins don't slip. I guess you could check the obvious, like make sure there's no grease or oil in the slots.

Might also try torquing the plate a little, such that the pins are preloaded in the clamped orientation, then close the chuck. You won't get much free space in the soft jaws when open, but that should be OK if your parts are consistent OD.

Regard.

Mike

Well much to my amazement I've just thoroughly de-greased the gizzmo with brake cleaner and although it has a slight tendency to slide back it's controllable.

I've not used it for a couple of months, and I expect that I gave it a spray with WD40 before I put it away in it's poly bag last time.

Very surprised though that it's so marginal, I'd have thought that the ramp of the cam groove would have been chosen such that this wasn't an issue.

However since I last used it I have been adjusting the chuck clamping force, so it is entirely possible that previously I was using it at a slightly lower squeeze !

If you're running bar stock, why do you waste time with the "gizmo"?

Just wind up the Chuck, bore them close to diameter, and run parts.

R

Rather than use some kind of boring gizmo to bore through jaws, I have always just used a thin plug at the back of the jaws. Bore down to the plug to the size I want, then remove the plug and relieve the area where the plug was.

The hydraulic chuck on this lathe can only be set ‘gripping’ or ‘open’ the logic doesn’t allow it to be left in an intermediate position, hence needing the gizmo. Were I to clamp on a plug at the rear of the jaws, bore to size, then remove it to turn off the remaining little step, the chuck would close preventing the boring bar entering

Set the chuck parameter to ID chucking.

litlerob1 said:

If you're running bar stock, why do you waste time with the "gizmo"?

Just wind up the Chuck, bore them close to diameter, and run parts.

R

Click to expand...

And to add to this, hard jaws are a worthwhile investment for running single ops (think part off complete), or first ops on raw bar stock. No boring required, adjust to the diameter you need and go.

andrewmawson said:

The hydraulic chuck on this lathe can only be set ‘gripping’ or ‘open’ the logic doesn’t allow it to be left in an intermediate position, hence needing the gizmo. Were I to clamp on a plug at the rear of the jaws, bore to size, then remove it to turn off the remaining little step, the chuck would close preventing the boring bar entering

Click to expand...

Yes, but only if you are doing pretty small diameter?

Booze Daily said:

Set the chuck parameter to ID chucking.

Click to expand...

Yep this works too.

Also, I know alot of people frown on this, but we used to do it all the time with no problem. If your chuck is in good/decent shape, you can clamp the chuck, bore your jaws, then move the jaws in one step (assuming these are serrated soft jaws) and be fine.

I have one of the Gismos and the first time that I used it I cut the pressure down but
it pulled the threads out of the little T nut.
I just use Pins that are a nice slip fit in the bolt Holes and then clamp on a short tube or ring.
Then u can fine adjust by turning down the ring or turn down the end of the pins.
Then u can use more pressure .

If I need to bore my jaws all the way through the ID, I will machine a face groove in the jaws to grab on a jaw boring ring. I have several sizes of rings made up.

It's a bit more work than just throwing that adjustable jaw boring gizmo into the jaw bolt holes, but I have no problems with runout with my method--even on a worn out chuck.

andrewmawson said:

The hydraulic chuck on this lathe can only be set ‘gripping’ or ‘open’ the logic doesn’t allow it to be left in an intermediate position, hence needing the gizmo. Were I to clamp on a plug at the rear of the jaws, bore to size, then remove it to turn off the remaining little step, the chuck would close preventing the boring bar entering

Click to expand...

That's why folks never throw-away old bearing races, is it not?

Make one of these. It's very accurate and absolutely eliminates bellmouthing, and you can back the knobs off just enough to allow entry of the stock. You just have to take the trouble to drill and tap your top jaws.