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Sine bar

A tool for accurately setting angles

 

 

Make parts out of a fairly stable material such as 1/4 inch Masonite. Assemble with dowels and glue. Sand dowels flush. The sine bar can be scaled to any size that is convenient. Keep in mind, however, that the longer the center distance between the disks, the more accurate it will be. Some points on accuracy. The center distance between disks can be any distance but as will be seen below, this distance has to be known precisely and for that reason, the distance should be a round number. The size of the disks themselves is not important, just that they be as close to exactly the same size as possible and the center hole be precisely in the center. Great care should be taken when drilling the holes in the bar for mounting the disks to ensure that they are as close to exactly the same distance down from the top as possible.

The formula to determine the height of the block for a given angle is as follows:

sin of angle multiplied by the center distance between discs.

As you can see, the accuracy potential is great. In the example above, if you miss cut the height of your block by 1/64, you would only have an error of .1033 degrees. The error would be even less if you used a longer bar.

The possibilities of this arrangement is only limited by your imagination. The bar could be a board, say, 12x12 with round rods running the full width. This would make a very accurate tilting table for a drill press. The top could be an angle plate enabling you to obtain the compliment of any angle. A thin bar such as that described here is best suited for use on it's side for setting fences, ect.