Stack height = sine bar length x sin(angle). A 5 inch sine bar at 30 degrees needs a 2.5000 inch stack; at 15 degrees it needs 1.2941 inches.
L is the center distance between the rolls, not the overall bar length. Accuracy falls off above about 45 degrees, because a small stack error becomes a larger angle error as the cosine shrinks.
Tools for this job
The tooling this calculation is usually for, spread across the price range.
How does the sine bar calculator work?
A sine bar turns an angle into a height, which gauge blocks can set to a ten-thousandth. That is the most accurate way a hobby shop can set or check an angle without a rotary table.
Frequently asked questions
What length sine bar should I buy?
A 5 inch sine bar suits almost every hobby job and fits a small surface plate and a 4 inch vise. A 10 inch bar halves the angle error for a given stack error, but needs a larger plate and taller stacks.
Keep going
Formulas are standard shop math; starting speeds are conservative conventions for hobby machines. Not professional engineering advice. Wear eye protection and keep hands, gloves and sleeves clear of rotating work.