Quote Originally Posted by mklotz View Post
Normally, the roll-to-roll distance of a sinebar is some simple value. 2.5, 5 and 10 inches are common values; the one shown in the picture is 2.5. But the roll distance can be any value SO LONG AS WE KNOW WHAT IT IS. If you make your own sinebar or inherit one of unknown accuracy, you'll want to measure the roll distance so it can be used when setting the sinebar to a desired angle.

One tool is needed - an accurate angle plate. They typically come in the form of 30-60-90 or 45-45-90 triangles. Every serious metalworking hobbyist should have one, preferably both.

If we replace the part shown in the picture with the known-to-be-accurate 30-60-90 triangle and adjust the stack height so the hypotenuse of the plate is parallel to the surface plate, we will know that the angle of the sinebar is 30 degrees to the same accuracy as the triangle.

The sinebar equation is:

sin(A) = S / L

A = angle
S = stack height
L = roll-to-roll distance

Solving for L then yields

L = S / sin(30) = S / (1/2) = 2 * S

Once the L value is calculated, it's worth writing it on the bottom of the sinebar with a Sharpie.

Speaking of Sharpies, they now make paint pens...

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

which make a more permanent mark than the ordinary Sharpie marker. Since they don't make an ordinary one with white ink, the white paint pen is a boon. It's especially useful when marking dark metals.
Thanks Marv for this adjunct to your above and finding out exactly what you have or build. To me it's an excellent thing to do because of the difficulty in making these exact lengths. Even the big names in metrology spend considerable time on this aspect, which is part of the high cost of theirs. Being somewhat leery of imports after my experience, these tests and some math will tell you what you have as best as your equipment will let you.

Also thanks for the link to the Oil based pens from Sharpie...makes sense they would jump on the band wagon. Have you tried them? Added them to my want list. Agreed about a choice of white but find Yellow contrasts on a lot of backgrounds too...the key is contrast I believe.