The following procedure is probably as old as the milling machine. It has been presented in many articles yet it took me a while to fully appreciate why it works. Writing this article clarified the facts for me.

I start with a block of metal with an irregular profile. Before I can cut to a precise size, it must be made square. I have greatly exaggerated the shape to make it easier to see how this procedure works.

The first step is to clamp the block in the mill vise with your smoothest face of the block up against the fixed jaw. If necessary, use a file to remove roughness that prevents solid bedding of face 4 onto the fixed jaw. A parallel supports the bottom along face 3. The parallel must be snug. Face 2 is compressed by the movable jaw acting through a short length of round stock. The round stock should be at least as long as the block is wide. Then proceed to cut face 1. Note that the cut face 1 is our first reference plane.

The block is now rotated so face 1 is against our fixed jaw, face 4 is supported by the parallel, and face 3 is compressed via the length of round stock by the movable jaw. Face 2 is now cut. Face 2 is perpendicular to face 1.

The block is again rotated. Now face 2 is against the fixed jaw, face 1 is down on the parallel. Face 4 should be reasonably parallel to face 2 so we remove the round stock and let the movable jaw come in contact with the block. You may notice that my parallel is larger in this figure. I was just too lazy to redraft the figures to be consistent. You should use the same parallel throughout in order to avoid error associated with using different parallels. We now cut face 3.

Our final step is to cut face 4. We now have all 4 faces perpendicular to each other. The ends are still uncut so assume they are not true. One way to true an end is to cut it with the side of the end mill used to cut face 4 before block is removed. You will have to made a few very light cuts in order to minimize bending of the end mill. Another method is to place a 1-2-3 block onto the ways of the vise and clamp it down. Then set the block on end with say face 1 against the fixed jaw and face 2 against the 1-2-3 block. Tighten the vise and take a light cut. This should put the first end, call it face 5, perpendicular to faces 1, 2, 3, and 4. You can now turn the block over and rest face 5 against the parallel. Make your final cut on face 6. You should now have a block with all 6 faces perpendicular to each other.

Comments and questions are always welcome.

Rick Sparber

Rgsparber@AOL.com