QT peteM: [The 22 tpi is one I'd be inclined to keep. A lot of the legacy Brit stuff has 5/16-22 threads.]
this chart is for 60* threads, is the British 5/16-22 a 60*? I did take 22 out but can put it back in.
QT ViedoMan: [FWIW, microphone stand adapters and other a/v devices use 27 tpi, and garden hose fittings use 11 1/2.]
Thanks, 27 and 11 1/2 are still in.
There are about 12 common metrics, from .2 to 1.5mm for m1.8x.2 to m18x1.5. I haven't decided if to include them or make a separate chart. I may have to go to the legal-size paper/ or go to a print shop special size.
Also, I have to check that I went to the greater size on each thread, so being minus the tolerance. Mostly I like to go about -.001 from max when I wire check.
This is why I posted this thread, To get some good advice. Thanks.
Since I understood the initial fractions such as a half, a quarter, an eighth I got the hang of it down to something like [SUP]307[/SUP]/[SUB]400[/SUB]". You can secure an unmistakable measure by an odd number numerator in the fraction. It’s a mixture of the decimal and the direct fractional system. I think people moved away from it after WWII towards the pure decimal inch measurement report like 0.375". I recognise ⅜" immediately by that.
I would keep my old chart but consider dropping 17, 19,21,23,25,27,29, and 30 along with 2 1/8, 2 1/4, 2 3/4, and the like. likely keep some of the even halves like 3 1/2, 4 1/2, 5 1/2, 6 1/2, and the like.
I could use a 17tpi setting on my lathe right now... its a lot closer to the metric thread I'm cutting than 18tpi which is my next closest. I'm hoping the 18tpi is not so awful that I have to make a changegear or buy a probably horrible ebay die and hope that it will cut.
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