PDA

View Full Version : Converting TPI to degrees



hornluv
12-02-2005, 10:42 PM
Is there a formula to convert taper per inch/foot to degrees? I've found charts giving a few common measurements, but I want to be able to figure out other ones.

Thanks,
Stuart

sauer38h
12-02-2005, 10:48 PM
Just the standard sine equations for triangles - is that what you're after? Sine of the angle equals the taper per foot divided by 12 (inches). Watch out for half angles - ie, is your taper on the radius or the diameter, and is the angle you want the full angle or the half angle. Depending on the answers to those questions, there are some "1/2"s floating around in there.

nheng
12-02-2005, 10:49 PM
-deleted duplicate-

[This message has been edited by nheng (edited 12-02-2005).]

Leigh
12-02-2005, 10:57 PM
Hi Stuart,

The tangent of an angle is the opposite side divided by the adjacent side (of the triangle). Thus the tangent = the taper on radius divided by the length, i.e. 1 foot. The angle would be the arctangent (inverse tangent) of that value.

Example: The tangent of 1/4" (on radius) per foot = 0.25 / 12 = 0.0208333. The angle is the arctangent of 0.0208333, which = 1.1935 degrees, or 1 degree 11 minutes 36 seconds.

To double-check (using a calculator): Enter 1.1935 degrees. Take the tangent, then multiply the result by 12. The answer should be 0.25.

------------------
Leigh

nheng
12-02-2005, 11:03 PM
Divide the taper by 2 then divide by the distance it is expressed over (per inch, per foot, etc.) using the same units.

On a calculator with trig functions, take the inverse tangent of your result ( could be "inv tan", "tan (to -1 power)", arc tan) as in this example:

taper = 0.5 inches per foot

same as 0.5 inches in 12 inches

divide by 2 = 0.25

0.25/12 = 0.0208333...

0.0208333 <inv><tan> = 1.1934 degrees

This is the half angle which the tool path follows. The full angle, if measured on the part, would be twice this.

added - double posted same info as Leigh while fumbling with the wording of the reply http://bbs.homeshopmachinist.net//wink.gif

Den


[This message has been edited by nheng (edited 12-02-2005).]