"Tim Wescott" wrote
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.

Then the handbook is providing too many significant digits in the
answer!


True, but I tend to believe Steve Walker's answer.

There is allot about machining that I do not know. Such as how to use
the angle to machine the taper, let alone measure it half way
accurately.