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pntrbl
04-25-2007, 11:04 PM
I'm getting ready to trim up a set of soft jaws for the first time. The jaws are 2 1/2" high and when they're rotating in a blur out there in space it sure looks like a crazy place to poke a tool into. I'm willing .... but I thought it'd be a good idea to ask if there's a good way to avoid hurting myself first!

Right now the jaw ID is smaller than the 2.1" part I'll be working on but not by much. Just a trim there. But I think I need to make 'em a lot deeper. Less than 5/8 now and my part is 1.75" long. Inch deep?

I know AL is usually a high rpm application but I don't think I wanna go there!

Thanx for any advice.

SP

wierdscience
04-26-2007, 12:30 AM
It's pretty simple,just rotate the chuck around by hand and bring the tool up to it,you can set the DOC off of that and use a DTI on the lathe ways to set the length of cut.

It's not an unknown if you know in advance how much of a cut you are going to take.

FWIW I usually don't take more than a .050" DOC on softjaws since the jaws aren't supported by a workpiece clamped in them.

Mark Hockett
04-26-2007, 01:01 AM
pntrbl,
Make sure you lock the master jaws on to something. I usually stick a socket on to an extension and stick it down into the master jaws. Then tighten the chuck on to it and remove the extension. Sockets come in many sizes so pick a socket that that fits your needs. When you get done and want to remove the socket just stick the extension back into the socket and loosen the chuck.

Gator
04-26-2007, 01:14 AM
Mark,
That's a heck of a good idea.
Should be in the tip book if it isn't already. It will at least go into mine.

Thanks.
Larry

pntrbl
04-26-2007, 07:29 AM
Loose jaws was one of the items on the nervous list. There's a just a click of freeplay on the scroll and centrifugal forces would probably take care of that, but I like locked down on a socket a lot better. Sliding it up by hand ahead of time is good too.

How can you tell when you've opened them up enough? Can't measure dia on a 3 jaw and I haven't a clue what dia they're cut for now. Should I just go by when the part slips in? Seems like a little on the oversize would be best for clamping anyway.

But what do I know? :)

SP

Bguns
04-26-2007, 07:39 AM
Bit undersize gives 4 points of solid contact vs 2 if a bit over.

Scishopguy
04-26-2007, 11:50 AM
You really need to clamp something in the master jaws, as Mark says. The play in the scroll will cause movement and give a less than satisfactory result, not to mention possibly breaking the tip off the tool. They make a set of steel rings that range in size from about 1" to about 4" that increase by 1/8's to do this but they are expensive and the same can be done with washers or scrap stock.

You want to make the pocket that you turn slightly smaller rather than larger than the part. It is better to grip on both sides of the jaw than just a point in the center.

Another handy thing about soft jaws is that you can use them on your indexer, on the mill, if you have the same size master jaws. It makes indexing holes in rings and plates much more secure. ;)

mochinist
04-26-2007, 08:09 PM
Bit undersize gives 4 points of solid contact vs 2 if a bit over.Maybe the beer is clouding my mind, but that makes no sense at the moment.

PolskiFran
04-26-2007, 10:04 PM
When I cut my lathe soft jaws I tighten the jaws against a homemade "spider". It is a hex nut with tapped holes in the center of every other flat of the hex. I thread allen cap screws into each of the holes for adjusting how far the jaws are to be spread apart. I can change the screws to accomodate different diameters.

Frank

jimsehr
04-26-2007, 10:20 PM
Think about it this way. If you bored jaws .100 oversize and gripped part in them you could the hold part but part only makes contact in 3 places on the part. But if you bore jaws 1 or 2 thousands under part size when part is loaded the 2 outside edges of each jaw make contact with part. So you have 6 contact points and this puts
part to center of bored jaws. And jaws will run truer.

Take a 1 inch Radius gage and hold it up to a .990 dia turned dia and gage only makes contact in 1 place on dia . Now take same gage and hold it up to a 1.01 dia turned dia and it will make contact in 2 places. This makes parts run much truer.
jimsehr

pntrbl
04-26-2007, 10:30 PM
Smaller it will be. I was thinking I'd get a clamping area by going slightly over instead of just the 2 points from an undersize. I guess I was wrong! LOL!

Thanx guys.

SP

wierdscience
04-27-2007, 01:02 AM
Loose jaws was one of the items on the nervous list. There's a just a click of freeplay on the scroll and centrifugal forces would probably take care of that, but I like locked down on a socket a lot better. Sliding it up by hand ahead of time is good too.

How can you tell when you've opened them up enough? Can't measure dia on a 3 jaw and I haven't a clue what dia they're cut for now. Should I just go by when the part slips in? Seems like a little on the oversize would be best for clamping anyway.

But what do I know? :)

SP

Oops,I though the use of backlash rings was commonly known,oh well I know never assume.

For sizing use the crosslide dial or an idicator.Setup the tool you intend to use for machining them and set it on center then zero the dial or indicator.Move the tool out a distance equal to 1/2 the finished diameter and then zero the dial again.Begin machining the jaws stopping a few thou short of zero,make the final pass at zero using a fine feedrate.

If you take care you should be able to hit the OD diameter of the part your fitting to within .003"

oldtiffie
05-14-2007, 12:19 PM
Deleted/edited-out