Need Help!- workholding headache on a CNC lathe

[david rendon]

Hello everyone, here's a good one...
I'm turning a R.17 on a 5.500" long hex bar (stainless) .... first I tried using a hex collet but the holding lenght of the collet is very short so the part swivels like crazy ...
second, I drilled a machinable collet and it works ok, but the problem is that I need to find the right spot where the hex bar is better centered.
Another problem is that the Radius goel all along the bar, that means that I have to turn this in 2 diferent operations...

Any ideas on how to hold this long hex bar?????

[jeffrey001]

You could buy a hex shape spring collet.

Jeff

[leggazoid]

Here are the steps I use to hold hex material centered in a 3 jaw chuck with soft jaws.

1: Install jaws with enough sticking past the OD of chuck for cleanup.

2: Clamp on a suitable size chuck ring or material laying around.

3: Turn OD of jaws.

4: Take jaws out and install machined end down in milling vise.

5: Mill the 3 jaws to the same height.

6: Put jaws in lathe chuck on the proper serration to clamp hex.

[jimmytightpants]

I would just stick it in a 3jaw and center drill it. flip it around and do the same to the other side. then turn between centers. flip around to finish the rest of the OD.

[david rendon]

I tried using an hexagonal spring collet, but the part swivels a lot !! .... I believe this is a good trick you guys might find interesting ....I ended up holding the part using a ER-16 collet extension (used regularly for milling purposes) .... It worked great!! (take a look at the pics) ....... cool isn't it ???

[gdwood3rd]

Call Hardinge Inc. in Elmira, NY - get hold of Rick Schoener and tell him George told you to give him a call. He will take care of you.