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[machinist] Helix angle math question

From: Lawrence London <lfljvenaura@gmail.com>
To: machinist@lists.ibiblio.org
Subject: [machinist] Helix angle math question
Date: Sun, 27 Dec 2015 22:06:33 -0500

Helix angle math question
http://www.practicalmachinist.com/vb/general/helix-angle-math-question-313788/

Helix angle math question

I looked through my machinist' handbook and couldn't find what Im after. How would you describe a helix angle if you know the circumference of the part and how many thousandths advance per degree of rotation? Is there a formula?
Thank you

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12-26-2015, 03:38 PM #2

Limy Sami
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000ths per degree X 360 will give you the lead per revolution, from then on it's a simple bit of trig.

I cheat and go here Trigonometry Calculator

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12-26-2015, 04:03 PM #3

Spencer in NH
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Tan(x) = opposite / adjacent

In this case "opposite" is the advance per revolution (the lead), and adjacent is the circumference (C).

C = pi * D, where D is the diameter. (pi=3.14159, remember that and you'll be fine.)

But, I digress....

So, the pitch angle x....

x = arctan ( lead / circumference)

On a calculator arctan is sometimes tan^-1.

For example.... a 1/4-20 bolt.... lead is 1/20 or 0.050-in.
Circumference is 3.14159*0.25 = 0.7854.
So, arctan(.050/0.7854)= 3.6426 degrees. QED.

Hope this helps.

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12-26-2015, 04:35 PM #4

James Lederer
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(Circumference/lead) tan^-1 = Helix angle. I use this all the time to calculate helix angles of rifling in gun barrels. My method gives you degrees off the axial axis of the part. For instance the helix angle of a 1/4-20 bolt using my method returns a result of 86.357 degrees. If you happen to have a TI-8* series graphing calculator I can share a simple program that calculates it.

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12-27-2015, 03:59 AM #5

EPAIII
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Helix Angle = arc Tan ( advance per degree * 360 / circumference)

[machinist] Helix angle math question, Lawrence London, 12/27/2015