On Fri, 21 Jun 2019 04:51:28 -0700 (PDT), "
wrote:

I am trying to help a guy who is opening a machine shop. Which is kind of comical since I have no experience in commercial machining.

He has a job machining peek plastic. And has a problem with long strings of the plastic jamming the chip conveyor. Now I am a novice but do know enough when confronted with a problem the first thing to do is find out what others have done. So how do you deal with strings of plastic?

When manual machining plastics I just pause feeding te avoid having one long chip. But maybe there is a better way. This is being done on a cnc turning center.

Dan
Greetings Dan,
I haven't machined PEEK but I have machined a lot of plastics. The
problem is not just that the plastic doesn't want to form a chip that
can be broken at room temp but since it is at an elevated temp from
being cut it becomes even more resistant to breaking.
What I have done with plastics that act the same way is to cool
the chip. Get it as cold as possible. Even cold coolant may be enough.
Not for UHMW though. At least I didn't have coolant cool enough.
It may seem exotic but CO2 can be use as a coolant and there are
systems made for using it. After reading about it years ago I tried a
setup for turning UHMW. I just used a 1/4 copper tube to direct the
CO2 to the tool.
I soldered a piece of brass into the tube and drilled it to make an
orifice. Then I opened a needle valve close to the tool and started
the cut. Using a heavy cut on the diameter helped to break the chip.
But I was able to defeat the chip breaking if the feed rate was too
heavy.
I had to turn my CO2 cylinder upside down to get liquid to flow out
because I didn't have the right kind of cylinder. And I used a lot of
CO2. Even though the experiment worked to some extent it was just that
and it was kind of a kludge with the CO2 cylinder being upside down
and resting on the ways and the end of the lathe. I shoulda taken a
picture because it really looked like redneck machining.
So if your friend is machining enough of this plastic it may be
worth it to look into really cold coolant.
There are also lathes that can stop the cut like you did on a
manual machine but I don't know what your friend has. They do this
very fast and are really expensive so I am betting your friend doesn't
have a machine that does this.There also may well be tools that do the
same thing.
I have a feeling that what will work the best though is some sort of
mod to the conveyor that will move the chips out of the lathe faster
so they won't have a chance to clog the conveyor.
Eric