Model Forum / General / Models / September 2008

Oh.  I should also say that, according to the same expert, the pulleys
on Taiwanese & Chinese Machine Tools aren't always correct to
profile.  The (supposedly) "A" section pulley on my lathe motor
allowed the belt to sit near flush.  He said it was newarer
"agricultural profile" than "A".  When I replaced the 1-phase motor
with a 3-phase/VFD on my Warco 1327 lathe (Taiwanese) I had to get a
new pulley to suit the motor spindle size difference.  Despite packing
the new motor out to give the same spindle position, I had to source
two new belts one size up.

BTW. Same expert said his belts are actually measured in metric and
labeled to the nearest inch.  When I was sourcing a belt for another
application, he was able to calculate the belt size for me if I gave
him the pulley diameters and centre to centre distance.  He converted
my imperial sizes to metric first.  Even so, the size calculated was
one size too small in "Inch belts".

Andy

from etpm@whidbey.com contains these words:

You need to re-apraise the way you read Machiery's handbook then. My
1923 Edition lists only 1/2" x 13 in the "United States Standard Thread"
but it does list 1/2" x 12 in the non-standard 'Sharp 'V'' form.

The latest edition still makes a reference to the Sharp V form but it
amounts to only 6 lines and comments upon the form being non-standard.

The Unified form in both Course and Fine series is what one would take
as the reference when discussing Screw Thread Series today and under
that standard 1/2" has always been 13 tpi  -  from 1/8" upward it is the
only one in the series that differs from BSW and that's the reason it
stands out.

The form of the thread essentially has no connection with the
diameter/pitch relationship of any thread series so it is fatuous to
refer to a 60° 'Whitworth' form.

Just because J&L offer 1/2" x 12 taps does not mean that they are 'Standard'.

Machinery's Handbook also lists the elements of the 'fixed pitch' series
which includes 12 tpi bu oddly enough it starts at 9/16"  -  so 1/2" x
12 doesn't even qualify there.

JG

s.

Of course 1/2" x 12 tpi are listed.It`s a standard thread.Not
preferred anymore but a standard just the same.If you look at a
British built machine,made pre 1970 it will be all BSW with a bit of
BSF.
As for finding BSW with 60 degree threads,no chance because if they`re
not 55 deg. there not BSW.

/SEARCH:KEYWORD/product.html. I

Where does it say on the description that they are 60 degrees?

You presumably all know that Whitworth, which is one of the earlier thread
standards, was arrived at by Whitworth collecting together all the examples
of threads he could find and taking an average.

Prior to the adoption of widespread standards, people just cut whatever
thread they had the tool to make.

Then you get funny things like the cycle threads, which are (almost) all 26
tpi, regardless of size.

I've got a big table somewhere with all the threads in (well, most of 'em)

How true!  I just spent a while cutting 100's of M79.50 x 1.5 pitch on
some brass spinnings.

Wayne....