Unusual Angles and Sine Plate Calculation

If you are making a custom part for your vehicle, in most cases it will not be shaped like a simple rectangle. Take a quick peek under the hood of even the simplest vehicle and you will find complex angles and curves due to the complex jobs that the parts accomplish. Most of us however, do not have access to a full machine shop with the most capable (and expensive) machines and computers. The equipment discussed below is the kind that you might find in a home machine shop, and will not completely break your budget.

Sine Plate
Here we will dive deep into fabricating angles and see how to make odd-size angles that may not exist in your standard box of angle blocks. To make things a little more interesting, we will find ways to make the angles very precise. For example, how would you make a 37.3-degree angle? No one makes an angle block with that exact measure, and the graduations on an angle vise just aren't accurate enough to find that last .3 of a degree. Don't be afraid. There will be some trigonometry involved with one of our specialized tools. But really, it's going to make things easier, we promise!


A tool that will allow us to make odd angles with extreme precision is called a sine plate. In actuality, it is two steel plates that lay flat and parallel to one another. Between them, at opposite ends are two metal bars that space the plates slightly apart. It looks, and functions much like a large door hinge. The bottom plate can be clamped to the milling machine table. The top plate hinges on one of the bars, and various precision-sized blocks can be stacked up under the bar on the other end to achieve our desired angle. The top plate usually has a number of tapped bolt holes in it, so that a small vice or the part to be machined can be directly clamped down.


Sine plates are considered precision tools. They are machined out of very strong cast iron or steel, and then hardened and ground to very precise dimensions. The steel bars that separate them are also hardened and ground.


This is because the distance between the bars is very important in the calculation of the angle. Sine plates are identified by this distance. For example, a 5-inch sine plate has a distance of five inches between the two bars. The actual size of the plates will usually be a little larger. The distance between the non-pivoting bar and the lower plate is also very critical. This is where blocks will be stacked to achieve your angle. Precision ground blocks can be purchased in sets that allow you to stack blocks together to have just about any height needed from .03 inch to 6 inches.