Griz G9249 (and maybe other) metric thread error
 

A search of the archives of this group for G9249 didn't bring up this
topic, so it may possibly be "new" info that seems worth sharing. I
recently had occasion to check the metric thread table on my lathe
(and in the manual) and noticed an error. That got me to wondering if
I could cut some of the other common metric pitches that weren't even
in the table. It's possible that the same error and omissions of
possible thread pitches have propagated to other similar 12x36/37 belt-
drive lathes. Anyway, here's what I found:

--The third column of the metric thread gearing, the one that shows
4.5mm thread pitch for quick-change gears set to 1A, should have a 30
tooth gear on the input shaft, as shown, but the output gear should
have 40 teeth, not 32 teeth. See page 41 of the Grizzly G9249 manual.

--For this lathe, and perhaps others with similar gear setups, here
are other common metric thread pitches you can cut either exactly or
with very small error (probably useful for short thread engagements):

(I don't trust how text formatting will come across in Usenet. The
following table should have five columns, and my intended headings for
the five, in order, a
--Thread pitch, mm
--Input gear (engages 127 tooth transfer gear)
--Output gear (engages 120 tooth transfer gear)
--Quick-change box setting
--Percent error in thread pitch)

0.2 32-teeth 40-teeth 6E exact
0.35 46-teeth 32-teeth 7E +0.31%
0.4 32-teeth 40-teeth 6D exact
0.7 46-teeth 32-teeth 7D +0.31%
0.8 32-teeth 40-teeth 6C exact
1.75 32-teeth 40-teeth 5B -0.26%
3.5 32-teeth 40-teeth 5A -0.26%

I have an Excel spreadsheet I used to calculate these (and basically
all other possible pitches) that I'm willing to share by email.

Cheers,
Tom