On Wed, 27 Jul 2011 18:46:58 -0400, "Stephen B."
wrote:

"Tim Wescott" wrote
On Wed, 27 Jul 2011 21:20:13 +0000, etpm wrote:

The standard taper 3/4 inch per foot is listed in Machinery's
Handbook
as 3, 34, 47. When I calculate it I get 3,34,34. I get this answer
using
my TI calculator and my computer. Looking on the web I find the
3,34,47
answer. It's the angle I've always used. So how come I get
something
different? On my TI-30X calculator I divide .75 by 12 which equals
.0625. This is the tangent. I then use the inverse tangent function
to
get the answer: 3.576334375. Then I use the DDDMS function which
returns the answer: 3,34,34 80. So what's going on??????
Thanks,
Confused machinist Eric

A long-ago typo that never got corrected? Was the thing on the web
a
table? Maybe they cribbed it out of Machinery's, complete with
typo?

I get your answer, by the way.


It is a question of significant digits.

0.75 in/ft calculated to 3 significant digits is 3.58 which comes out
to exactly 3 deg 34 min 48 seconds.

the math you are calculating is the equivalent to 0.750000000 in/ft a
far more precise taper.
Thanks Steve and Tim for your replies. It seems that the table on the
web for prop shafts AND Machinery's Handbook are wrong. Kinda destroys
my faith in Machinery's Handbook. It's the first mistake I've ever
found in it. Maybe I should write them a letter.
Eric