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Milling machine – workholding – cylindrical squares
A cylindrical square is simply a piece of round bar whose sides are at right angles to its ends. But it is a precisely made component. The sides must be parallel and the ends must be square to the sides. It has a hole through its center. This means it can be bolted to the table of the milling machine. This gives a touching surface at right angles to the table. If there are two of these clamped to the table then another flat surface touching both of the cylindrical squares will also be at right angles to the table.
The beauty of the cylindrical square is that they are easy to make and only need the simplest of lathes to make them.
see Lathe – making – cylindrical squares
Fig. 310 Pair of cylindrical squares 402
Using Cylindrical squares
Making an angle plate
Having made two cylindrical squares it is possible to make an angle plate from a casting. On a vertical milling machine it is only practical to mill a large flat surface if it is parallel to the milling table.
An angle plate needs two flat surfaces at right angles to each other. To start with there are two rough surfaces. The first surface is cleaned up with a file so it will sit flat on the cylindrical squares. This surface is clamped to the cylindrical squares. The second surface, which is now horizontal, is machined so it is flat. The angle plate is removed from the cylindrical squares. The flat surface is now clamped to the cylindrical squares. The top surface is now machined. This surface will, by definition, be at right angles to the other surface. The result is two flat surfaces at right angles to each other – an angle plate.
Fig. Using cylindrical squares to hold an angle plate casting 553
fig Finished angle plate 563