How do I throughbore softjaws for a hydraulic lathe chuck?

[MadMax]

I've just gotten a nice Daewoo and am in the process of setting up my first job. I'm stuck at boring the soft jaws. The manual describes a process of clamping a piece of material in the jaws before using a boring bar to turn the tips round.

I need to run bar stock in the spindle. How do I do the turning all the way through the jaws with a piece of material stuck in the jaws? Is it possible to just close the chuck and let the hydraulic bottom out or would I not achieve a concentric bore?

[MadMax]

Nevermind. I used the search tool like I should have before making this post. It looks like I need to get a boring ring or improvise somethign similar.

[morehelium]

I'm not sure if this is what they are referring to, but this is a pic of a piece I made to preload scroll chuck jaws to grind them. It might have to be designed a bit stronger for a hydraulic chuck.

[morehelium]

oops, you posted your nevermind as I was looking for a pic and typing...

[MadMax]

That's interesting. Am I correct in thinking that you need to make a new ring for a certain range of bore diameter?

I ended up ordering one of these: http://monster-jaws.com/ebay/monster...oring_ring.jpg

I think I'll be doing a lot of different setups this coming year so I decided to get something adjustable.

[MadMax]

Why couldn't I just close the chuck and bore away? My chuck isn't a scroll type so there isn't any play. Is it because hydraulic chuck jaws don't bottom out evenly?

[mactec54]

Hi MadMax

You could of made just a ring that fits the ouside of the jaws you first clamp a piece in the jaw skim the outside to clean up & make your ring close to this size & you will use the ring on the outside every time you need to change the jaw profile

[Geof]

Originally Posted by MadMax Why couldn't I just close the chuck and bore away? My chuck isn't a scroll type so there isn't any play. Is it because hydraulic chuck jaws don't bottom out evenly?

There is play, a really small amount, and there is deflection again a really small amount. If you just close the jaws and bore the soft jaws then when the soft jaws are in use the play and deflection add up so the tips of the jaws are not gripping quite as tight as closer to the chuck body. Loading the jaws with a boring ring means that the boring is done with all the play and deflection taken up so it can produce a more parallel grip.

It is something of a picky point and some people simply say it is not worth worrying about; I apply the principle that if I don't do it and it is needed I have screwed up but if I do it and it is not needed everything is fine.

[flick]

Originally Posted by MadMax Why couldn't I just close the chuck and bore away? My chuck isn't a scroll type so there isn't any play. Is it because hydraulic chuck jaws don't bottom out evenly?

Some are better than others. With various machines in my shop I can count on anything from around 0.0015 to over 0.005 TIR after boring the jaws without a clamping ring. Some of this is due to uneven bottoming, and some is due to uneven flex in the jaws under clamping pressures due to varying degrees of wear in the jaw guide and varying degrees of serration quality in the jaws themselves.

Take a light skim without a ring and see what you can get away with.

[MadMax]

Ah so. The angels chorus and I have some better idea of why jaws should be cut under load.

I just watched this video to get a better appreciation of how a hydraulic chuck worked.

YouTube - Reassembling a Kitagawa B206 Chuck

YouTube - Reassembling a Kitagawa B206 Chuck

It appears that under no part load, the jaws mounts don't bottom out on anything when the draw tube plate pulls up against the inside of the back mounting plate. Besides a bit of sliding play there's also a little bit of lateral play in each jaw block track.

It seems to me that using a jaw boring ring gives the jaws something to bear against to eat up this play during the boring. I wonder if I should be pushing the jaws open against the boring ring when setting up for OD clamping. I'm thinking that a tip load on the jaws from the boring ring would result in a little runout in the jaw surface so it'd be a bit conical. Boring with the jaws pushing open would put the smallest diameter at the ends of the jaws instead of the root so whatever small amount of play would give more contact from the tip to the root than if the jaws were being closed against the ring which would make the diameter at the tips larger.

[Geof]

Originally Posted by MadMax ... I wonder if I should be pushing the jaws open against the boring ring when setting up for OD clamping. I'm thinking that a tip load on the jaws from the boring ring would result in a little runout in the jaw surface so it'd be a bit conical. Boring with the jaws pushing open would put the smallest diameter at the ends of the jaws instead of the root so whatever small amount of play would give more contact from the tip to the root than if the jaws were being closed against the ring which would make the diameter at the tips larger.

Methinks you have it backwards.

You want the jaws loaded during boring in a manner as close as possible to the manner in which they are loaded during use.

The most extreme situation during use is when a part is being gripped by only a small length at the tip of the jaws; this is the situation you replicate with the boring ring.

[mactec54]

Hi MadMax

You are right sometimes the ring on the outside can give you a bad bore only if the chuck is in bad shape the other way to do it is clamp on a short piece of bar & place this at the back of the jaws bore the hole size you want up to the piece in the jaws now that you have the bore you want take the piece of bar out of the chuck then bore the back of the jaw with a slight under cut making the bore at the back of the jaw were the piece of bar was a little bigger dia & when clamping on a piece like this only use enough pressure to get the job done to hold the piece of bar in place