DIYbanter - View Single Post - Cutting threads on the inside of a 3" socket end of PVC pipe

On Sun, 22 Jan 2006 22:34:49 GMT, (Roy) wrote:

I am in the process of making an item for my sal****er setups, and
have to thread the inside diam of a 3" socket joint (happens to be
correct bore needed for my application and only needs threads) which
are 13 tpi. My biggest problem is if I tighten the piece up in the
chuck it distorts it. I ruined a bunch of pieces trying to find a
sweet spot n chucking prressure with out distortin oor without having
it slip. Even with light cuts its gone wrong. Perhaps I need to put it
all away and give it a try on anaother day, unless someone can suggest
something that may work to hold this piece in the chuck without
distortion or slipping. I have played with super glueiing it, double
faced tapes, but one thing I have not tried net is to glue two or
three lugs on the outside of the piece I am turning and allow them to
hold against the chuck jaws sides.........hmmmmmmmthat idea just hit
me, is there anything else that may work?

PVC is neat to machine, but it can get awfull flimsey and such when
chucked up.....
You can make "pie jaws" for your chuck. These are shaped like sections
of a pie. Use sections that are 120 degrees. Close them until the
sides almost touch and then bore to fit your part. These will hold
your parts with small enough distortion, and with enough grip, to
single point your threads. Another method would be to turn and bore a
piece of good wood (not pine, but maybe poplar?) so that your part
just slips into the wood piece. Make one saw cut so that the wood can
grip the plastic when the chuck jaws tighten. A 3/4" wall on the wood
piece should be adequate. If slippage does occur then glue some fine
sandpaper to the wood in the bore. 320 or 240 grit would work fine.
ERS