Form angles with a combination square

[mklotz]

If you have a combination square but didn't spring for the (often expensive) protractor head you can still use it to measure or set angles.

If you imagine a flat spanning from the end of the head to the end of the beam/scale, you've created a right triangle; the head and beam are always perpendicular.

The head length is fixed so it can be measured; the beam length is, of course adjustable. The math is simple...

H = head length
B = beam length
A = angle desired

tan (A) = H / B

so:

B = H / tan (A)

Knowing our desired angle, A, and measuring our head length, H, we can calculate the beam extension, B, to form A.

In this photo...



I measured H to be 3 & 7/16 in and calculated the beam length needed to form a 30 degree angle...

B = 3.438 / tan (30) = 3.438 / 0.577 = 5.954 in ~= 3 & 15/16 in.

I set the beam to that length and then measured the angle formed with an electronic inclinometer...



OK, it's not perfect, but close enough for many applications, especially if the more accurate tools are not to hand.