NO 26TPI THREAD CUT SETTING

For the record, the error is rough three time the amount by which the length of an inch changed in July 1959 when it became exactly 25.4 mm.

**LINK**

So if that error worries you, you probably work for the NPL or CERN...

Neil

page not found error 404

Stuart

.

Thank You.

MichaelG.

Try: www.npl.co.uk.../on-what-basis-is-one-inch-exactly-equal-to-25.4-mm-has-the-imperial-inch-been-adjusted-to-give-this-exact-fit-and-if-so-when

Neil

Now if you really want to be clever Neil you could tell us what temperature we need to get the workshop and workpiece upto when we cut the thread so that as it returns to normal use temperature it will shrink to the exact pitch required

Hi Jason,

The answer appears to be one degree C/K! Did you know that already?

Neil

The handbags are out .

"use temperature it will shrink to the exact pitch required" lol

No

But does that apply to all materials? I would have thought you would not need to get a copper rod as warm as a steel one

AArgh Jason! My brain is already starting to dribble out of my ears!

Neil

Back to the subject, I just worked out if my 280 can cut 26tpi.

40 spindle driving 65T = 0.6153846

50 driving 80 = 0.625

60 driving 75 on the leadscrew = 0.8

0.6153846 x 0.625 x 0.8 = 0.3076923

0.3076923 x 26 = 7.9999998 which is good enough for me and my 8tpi leadscrew provided I do it when Good Friday falls on a Thursday

EDIT if I use the Windows calculator that gives the 40/65 to far more decimal places it comes out bang on 8

Edited By JasonB on 11/11/2014 20:56:30

No need for decimals, or calculators:

40/65 x 50/80 x 60/75 = 8/26

Purely integer arithmetic.

Andrew