I.D. chucking problem

I read this site almost every day and know someone has an answer for my problem. I am machining some yo yos for a guy and I am turning the O.D. second operation. I have little to no experience I.D. chucking.

Part is delrin with about .250 wall thickness. Part has a .047 deep groove .094 back. I have bored a set of jaws and with the chuck pressure all the way down (about 50 pounds) the part comes off with 3 steps where the jaws have pushed and cut more material away at the jaw spacings. My question is how do I get this to not push out so much?

Thanks in advance. Michael

Use an expanding mandrel to hold on the ID.

RAS

So, you have a through hole? Sounds like you may be able to machine a plug with a drilled and tapped hole in the end, and mount the ID of the YO on it, fasten the YO on with a washer and SHCS. That way you won't deform the ID and you have easy access to the OD.

RAS, you posted while I was still typing.

RAS,
I purchased one but can not seem to get it to expand more than a few thousands. This collet system I have never used. Got it from US Shop Tools. It is for a 16C collet nose.
Michael

hess no through hole. Flat on I.D. only goes back .200 with .094 of that is the lip. Has some wierd angles and a pointed cone on the center.
Michael

I've worked with 5C expanding collets that were troublesome; sometimes they didn't grip/release well with drawtube pressure alone. Does yours have a tapped hole and cap screw in the center of the outboard end? If so, use that for tightening/loosening.

On Edit: Ah, no through hole... can you post a pic of the part?


RAS

Silly question. Did you undercut the back side of the soft jaws to take out the tool nose radius? Also, when you made your soft jaws did you chuck on a piece of material at your selected chuck pressure to turn to the internal size of your parts?

mthomure, are you using full wrap jaws ?? If so, this is what you need to do. First you need to have your jaws as close together (in the closed position) without hitting each other first. Then you need to turn the jaws for a ring that is larger than the od. of your part your making. (the id. of the ring should be aroung .020-.040 bigger than what you turn them to). Chuck the ring (id) and turn the jaws to the same diameter as you have on the id. of your part. Put an indicator on an area that was machined in the previous operation if you can and check your runnout. If is not an exceptable amount then recut the chucking diameter that you made for your ring another .005-.010, chuck your ring again then re-cut your locating diameter. The principle is the same as od. full wrap, but by chucking in the other direction. You should cut your jaws at the same chuck pressure your going to us when machining the part. If your not using full wrap jaws, i suggest that you get some, with that wall thickness you'll be tri-lobbing your parts and they won't come out right.

RAS, it does have a screw in the center, but when I tighten it up the part will not go on the smaller dia. I'm not sure how to post a picture on here. I can e-mail it to you.

dabigguy, I did undercut the jaws, but not the expandable collet yet as I can't see it moving when I open and close the chuck. I did clamp on a plug when I machined the 3 jaws at slightly more pressure,but not that much more.
Michael

mthomure,
Procedure for cutting expanding collet:
1. Front screw should be snug, but not tight (finger tight + 1/8 turn).
2. 'Close' collet @ desired pressure, machine to .001/.002 bigger than ID of part.
3. Open collet, check fit with part; adjust front screw, if needed.

Email your pic to: [email protected]. If the collet won't work, I think I can get you going using the 3-jaw.

RAS

If you want to grip things by the inside you should look at the Hardinge SureGrip expanding collet set-up. We are using a series 400 A2-6 mount in production. I can't say enough how well these work.
These are priced reasonably and they kick ass!

You can find them by following the ad at the top of the page for Hardinge Workholding.

I just reworked some thin wall injection molded parts and it worked great. The collets have a 1/64th grip range. I set up a limiting collar so that I would not overstretch the parts. Fantastic results.

We also grip a part that is 1.688 ID and 9.75" long. We cut a 1.875-16 thread on the far end of these with no chatter. I should shoot a short Vid sometime.

ARB

Thanks for the ideas guys. I am going to make a ring to fit inside of the I.D. groove or undercut and the fit the O.D. of the expanding collet as RAS suggested. I like the idea of having 360 degrees of contact.
Michael

To all of you that offer advice I appreciate it very much. I made a split sleeve to go inside of part to clamp on I.D. groove and it seems to be working. Run out is within .001 (very acceptable) so I am confident this is the best solution for this run of 150 pcs. Again thanks for all of the suggestions. Even the ones I didn't use this time I have stored the information in case I need it for some future project.
Michael