long chuck jaws
long chuck jaws
(OP)
We currently produce plastic parts in various hardnesses.
Machining some of these parts is proving tricky.
They are soft enough that when facing off bungs 14" long 7" diameter they flick out of the lathe chuck.
We cannot use a center (we're facing off) and a steady will melt the plastic.
Milling doesn't work as the plastic crumbs or melts.
We think that chuck jaws that protrude, say, 10" from the face of the chuck would work, but can these be bought anywhere, or are we barking up the wrong tree?
(It's a Rohr three jaw chuck on a DSG Type 17 lathe).
Thanks.
Machining some of these parts is proving tricky.
They are soft enough that when facing off bungs 14" long 7" diameter they flick out of the lathe chuck.
We cannot use a center (we're facing off) and a steady will melt the plastic.
Milling doesn't work as the plastic crumbs or melts.
We think that chuck jaws that protrude, say, 10" from the face of the chuck would work, but can these be bought anywhere, or are we barking up the wrong tree?
(It's a Rohr three jaw chuck on a DSG Type 17 lathe).
Thanks.





RE: long chuck jaws
That's about all I can offer, I am not a machinest by trade or avocation. I admire those who have tried over the years to teach me.
Rod
RE: long chuck jaws
RE: long chuck jaws
RE: long chuck jaws
to try. Maybe a piece cut from an old inner tube?
Being a crotchety old yankee, I like to try the
easy & cheap things first.
RE: long chuck jaws
http://www.ringspann.com/uk/products/p13_16/p13zst.htm
RE: long chuck jaws
Rod
RE: long chuck jaws
RE: long chuck jaws
Simple set-up in v blocks for side milling using an end-mill, or ing the head of a bridgeport over so you can attach your plastic cylinder pointing down over the side of the table and face mill (fly-cut)it.
Slow down (melting), climb cut (with axis brake on if necessary), and use coolant! Everyone cuts plastic dry or with an air blast like those instructions came down from the mountain on a stone tablet, but I cut them wet and never have problems of melting - even at 15,000 rpm and 3/4 endmills. (THAT is done in an enclosed cnc.)
Choose a compatible coolant, mix it up with water, pump continuiously as you cut. I use flood coolant, not mist.
You have to use sharp cornered tooling,double positive rake, like for aluminum. Negative rake tooling for steel will melt most thermoplastics every time, even with coolant.
The coolant will prolong the life of those fine sharp edges too, something that plastics typically tend to erode quickly. I won't tell you WHY the coolant will help so much just yet, but it's not it's lubricity that saves the edges, I've found it's something far less obvious, but a powerful factor non the less.