This is made from 4mm thick plywood or similar and is five times the size of the cam to be ground, and geometrically similar. The centre line of the master cam must be clearly scribed as this will be used for setting up when the machine is in use.I made four master cams for the inlet and exhaust cams for my 5 and 10cc engines, photo 9. To make the master cams, I printed off the cam outlines from the CAD model five times the size of the actual cams, checking the dimensions on the finished print outs. The paper prints were glued to pieces of 4mm birch ply using wood glue and weighted down to stop them from distorting. The outlines were then roughly cut out with a saw and then carefully cut to size holding the edges of the cams against the sanding machine. It was necessary to cut down from the paper side to avoid the edges of the paper curling up. I tried to sand up to the line, keeping the sanded edge square to the face, photo 10. The edges were checked for irregularities and finished with fine sandpaper. The holes through the cams were marked with an awl and carefully drilled to size using progressively larger drill bits, starting with a very small one to ensure positional accuracy. A scrap piece of ply was used as a backing to prevent breakthrough, photo 11 shows the completed master cam assembly parts.
展开▼
