Channeling Tool

This is used in forming the squares in the pitch lap (Fig. 16). It should be at least 8" long, with a cross section like that shown in Fig. 16. A length of channel iron of these dimensions, or slightly smaller, will do, or the channeling tool may be made out of wood. It will not be needed if a molded lap is used.

Grinding Stand

Considerable friction is encountered in polishing, so the grinding stand must be rigid and heavy. A weighted barrel with a reinforced top will do nicely. A stand like that shown in Fig. 17 is sturdy, cheap, and easily put together. A 36" to 40" length of 2½" or 3" pipe, screwed into a heavy flange, is set in a block of concrete. Another heavy flange is fastened to the heavy wooden top with small lag screws, and screwed tightly to the upper end of the pipe. A small cabinet in which to store the abrasives may be built in around the pipe.

Mirror Testing Rack shows a conventional form. The mirror is supported on two dowel sticks spaced about 4" apart. The rack rests on two pegs at the back, and on the adjusting screw in front, which is used to tilt the mirror up or down.

Testing Stands Measurements will have to be made in hundredths of an inch, so the testing stands must be sturdy, and rest solidly on the floor. Any vibrations which result from passing trains or other traffic may sadly disrupt testing, so a concrete floor is preferred. If stands have to be built, they should be designed
so that testing can be conducted in a comfortable sitting posture, and so that the center of the mirror, pinhole, and knife-edge are all at about the same level.

Foucault testing and theory