Re: A big ol' chunk of delrin

On Mon, 21 Apr 2025 16:49:06 -0500, Snag <Snag_one@msn.com> wrote:

On 4/21/2025 2:37 PM, Joe Gwinn wrote:

On Mon, 21 Apr 2025 13:44:28 -0500, Snag <Snag_one@msn.com> wrote:
 

On 4/21/2025 10:19 AM, Clare Snyder wrote:

Don't be a wuss -chuck it in the 4 jaw and single point it. If you
grind your tool right you won't even need to heat form it - - - -
>

>
   The problem with that is that I'm not certain what the thread profile
is - probably acme but ... I was just thinking that I can make an
impression of the leadscrew , wax might work or clean the leadscrew well
and apply a release compound and mold one out of JB weld ... and use
that impression to grind a cutter . That piece of plastic is dialed in
on my 4 jaw , and ain't coming out just yet .

 
 From the discussion, I'd guess that it may be a ISO Trapezoidal
thread, specifically TR24x3.
 
.<https://www.engineersedge.com/hardware/iso-metric-trapezoidal-threads1.htm>
 
Otherwise, it's likely an Imperial Acme thread, 8 TPI.
 
Measure the thread pitch to tell.  3mm pitch is 8.47 TPI, a ratio of
1.058 compared to 9=8 TPI, which is easily distinguished over the
length of the leadscrew.
 
Joe
 

>
  It's definitely an 8 TPI leadscrew , moves the table .125"/revolution
plus/minus a few tenths . OD is within a few thousandths of 15/16" .
Tell me more about this imperial acme thread ... this machine is a copy
of the RF45 , made in China in 2001 . I got it new IIRC in '02 or '03 .
I've made a lot of stuff with this machine .

In the US, Imperial (meaning inch) Acme is better known as ANSI Acme,
as documented in Machinery's Handbook.  The biggest standard ANSI Acme
is 5/8-8 Acme, which is only 5/8" in diameter, not 15/16", so we may
have a franken-thread here. 

Cutting one thread or the other into the same size leadscrew blanks
would make production sense.

The cleanest way to tell is to measure the pitch diameter with three
identical number-drill blanks and a micrometer on some unworn area (so
the flanks are good).

.<https://www.engineersedge.com/hardware/external_acme_thread_13360.htm>

Joe


PS:  It may have been Ox Tools who did a video on melting delrin to
make a new nut to fit an existing leadscrew.  JG