Newsgroups: rec.crafts.metalworking
Subject: Re: making a die?
From: Robert Bastow <Tubal_cain@hotmail.com>
Date: Mon, 19 Oct 1998 06:05:31 GMT

ddouglas@dibbs.net wrote:
> 
> Bill, The trouble with using a die, is that it will cut off some of your
> thread making it weaker.  A friend told me how he had fixed a thread on
> the front spindle of an antique car.  He bought a box of the correct
> size nuts and screwed them on the spindle one after the other.  Each nut
> was destroyed at the start, but gradually, the thread was "formed" back
> into shape.  Of course, a die might be cheaper than a box of nuts.  But
> this worked in his situation.  Doug

The best way to "reform" rather than "recut" an old, buggered thread (or
a newly cut one for that matter,) is to buy or make a "nut" of the same size and
start to screw it on.  Each time it starts to get tight, rap it smartly, all
round its circumference,  until you can turn it further..Each time it STARTS to
bind, repeat the tapping process.  It can take a while but you will get an
almost perfect reformed thread out of it.

I do this with every thread I cut, rather than trying to cut it to "dead size" 
Because of minor imperfections and burrs, a dead size thread will almost always,
settle down to being oversize after an nominal amount of running in.

Robert Bastow

From: Robert Bastow <teenut@home.com>
Newsgroups: rec.crafts.metalworking
Subject: Thread chasers for "single pointing"
Date: Thu, 07 Oct 1999 18:40:18 GMT

A tip (trick,technique..call it what you like..) that I learned as an
apprentice, is to use a die head chaser as a "multi-point", single point screw
cutting tool.

This way, the thread form is always dead on,as geometric type chasers ar form
ground very accurately.  This feature alone is invaluable when cutting whitworth
form or other radius root/crest threads.

I have made special holders to clamp my chasers in..just a slot, milled in a
chunk of keystock, with a couple of setscrews to hold the chaser.

I grind a rather longer "lead" on some chasers, especially the ones in "Boring
tool" type holders, that I use for threading internally. Others, for threading
up to a shoulder, I leave with a short or zero lead.

"single, multi-point" threading is a joy..most threads up to say 20 tpi, can be
cut in a couple or three passes, dead to size..no need to swing the compound
over to half thread angle...A practice almost uniquely American, and virtually
unheard of in the UK.  I was taught, and till do, leave the compound parallel to
the thread axis.  On large threads the compound is advanced a half a thou or so
with each pass..this having the effect of relieving the trailing flank of the
cutting tool.  Much faster to set up and to do..Makes the math a lot simpler
too!

An alternative technique is to let the hand gently "Brake" the carriage hand
wheel on every alternate pass..this has the same effect of allowing the thread
tool to cut mainly on one side.  Don't do this if your leadscrew nuts are badly
worn though..you will wipe out all trace of a thread!!

These techniques, especially in conjunction with a "Rapid Tool Withdrawal"
device..such as fitted to Hardinge and many other high class lathes, enables
accurate, correct form threads to be produced faster than it takes to write
about it.

Over the years I have collected pretty well a full set of chasers for
"single-multi pointing"  both for internal and external use.  Usually these can
be had for free from your local screw machine shop..you are only interested in
one or two, and they need a full set of four.  When one of a set is damaged, or
they are ground down too far for production use..they heave them in the scrap
bin!!

Bear in mind, you don't need a chaser for every thread SIZE!  A 1/4 - 20 chaser
will happily cut 3/8" 7/16" 1/2" by 20 threads too!  All my "Special threads"
are 12, 20, 32, or 40 TPI, depending on application, so four chasers covers the
lot.

Happy threading

teenut