On 23/07/18 19:41, Jim Wilkins wrote:
"David Billington" wrote in message
news
On 23/07/18 15:34, Jim Wilkins wrote:
I filled out the less common sizes in my tap and die collection
from
the bin in a second-hand store, without regard to the OD of the
dies,
since I'd probably only turn them by hand to repair existing
threads.
Recently I got out the 1/4-18 NPT die to clean up rusty threads and
noticed that it was missing the adjusting screw that holds the die
open against the pressure of the diestock clamp screws.

The die is 1.5" round and the adjusting screw enters radially into
the
slot, not perpendicular to the slot on a chord like normal split
dies.
I made a 32TPI screw which fit when turned to 0.295" OD, not much
more
than 0.281" or 9/32" which is a standardized thread:

https://www.amazon.com/Special-Threa.../dp/B0141JFGRM
The die manufacturer is Card, USA.

The female adjusting screw thread in the die is noticeably tapered.
Since this is a pipe thread die the exact cutting size doesn't
matter
and the die OD is under 1.500" with the home made screw fully
inserted, but I have other similar dies for straight threads and
adjusting then to cut the right size without a gauge would be
tedious
if my custom setscrew is out of spec..

Does anyone have this type of die to measure or know whether or not
9/32-32 is the proper thread size for this adjusting screw?

Thanks
-jsw


I can't help with your specific query as none of my pipe threading
dies are split they just have a notch or notches to prevent rotation
and are of a thickness to suit to intended thread size length. I
presume they are all accurately made so that when run onto the pipe
to cut the thread when the die is flush at the end of the pipe the
gauge size of the thread is correct hence no need for adjustment.
All are Rotostock pipe threading dies to suit the Rotostock machine.

I thought dies were split so they could be tightened back to size
after grinding inside the holes to resharpening them. I resharpen old
taps by running a cylindrical stone in the flutes.

Anyway, rather than leaving the lathe set up I made some 9/32"-32
setscrews which seem to fit well. The Schrader valve and 5C collet
show that thread diameters can't be assumed.


Quite possibly although the pipe thread dies I have would require quite
a bit of dressing back to significantly effect the pipe thread size cut.
IIRC both NPT and BSP pipe threads are 1:16 taper on diameter so I think
would be fairly tolerant to dressing and still give usable thread
engagement but I've never had to dress a die yet.

I do use the adjustment feature with split dies with straight threads
and one application for threading M10 x 1 on stainless tubing I made a
double ended die holder with one die set for a roughing cut and the
other die set for a finish cut, works very well. The die holder locates
on a mandrel which fits in the tubing for alignment. That and using
decent high pressure lubricant when cutting threads I haven't had to
replace a die yet.

Most of my taps are small enough that if blunted for some reason it's
easier to replace but I'll bear in mind the sharpening for some larger
ones that are losing their edge from cutting threads in some poor
quality steel.