I am revising my thread chart and wonder if I should drop some now uncommon threads.
For example, the old Hendy Norton thread plate had 2, 2 1/8, 2 1/2, ..and some lathe plates go to 224 TPI.
I am thinking that I might just use the threads given on a high-quality modern lathe, and dump many of the oddball threads...
Here is an example of an old tread plate, on page 16:
Seems like a modern lathe might have 44 standard threads 2 to 72, and 39 metrics .2 to 14
that is still a lot of threads.
I have used 127 tpi for steel screw, making a tap and a "split brass nut" that is tightened to grip screw tight.
the threads are so fine they dont look like threads more like a medium coarse turning
the front of sharp V cutter (not top) is forced into metal it basically is knurling or cold
forming the metal to create threads, pushing metal around tends to increase dia. I used a anti seez
thread compound as "threading oil)
this 127 tpi thread was for a optical instrument, rather than a differential thread screw i had a
single thread screw, the split nut needed periodic adjustment if it opened too far the screw
wouldnt engage the nut threads
really old lathes just cause it said it was at 40 tpi if measured over 10" you might have 399 or 401
threads. when thread pitch not same on screw and nut the more screw is screwed into nut the tighter
the threads feel.... just saying I could see somebody trying a "odd" screw pitch so it matched better
that is new screw into old nut
or new nut for old screw
..... just saying even 24 tpi and 25 tpi is close enough to maybe not notice, short of counting threads
per 1 or 2 or 3" distance
for making replacement parts for old machines the old machines might be full of odd threads like 1/2-12 not 1/2-13
sometimes they deliberately used odd threads for the replacement part so they had to be bought by the
original tool maker. Starrett used to use odd threads on their precision levels not sure if they still do
i seem to remember 12-24 thread being used