Accurate angles without a sinebar

[mklotz]

A sinebar is the preferred tool for setting up to mill a precise angle but not every amateur has one. Also, while they're good for setting the angle, it's not the best idea to use them to support the work while milling. Most amateurs have a lathe and the measuring tools to turn a cylinder to a precisely determined diameter. Here I discuss how to use this ability to build a jig to support a workpiece at a precise angle for milling.

If I take two cylinders of diameters d1 (smaller) and d2 (larger) and lay them in contact with each other on a horizontal plate, a flat plate placed across them will form an angle, theta, with the horizontal given by:

d1 = d2 * (1-sin(theta/2))/(1+sin(theta/2))

So, the procedure goes like this. Given the angle, theta, and the diameter of the larger cylinder, use the formula above to determine the diameter of the smaller cylinder, d1 (a scientific calculator will be a great help here). Machine a cylinder of diameter d1 on the lathe. Arrange the two cylinders in contact with each other in the milling vise and place the work on them. The work will thus be tilted at an angle of theta.

Here's an example case you can use to prove to yourself that you understand how to perform the calculation...

d2 = 0.75"
theta = 1.5 deg
calculated d1 = 0.7306"

If the math is too much for you, there's a program to do it in the SINE.ZIP archive on my page.

[DIYer]

Thanks mklotz! We've added your Mill Angle Setting Without a Sinebar to our Measuring and Marking category,
as well as to your builder page: mklotz's Homemade Tools. Your receipt:

Mill Angle Setting Without a Sinebar by mklotz

tags: angle, measurement