The form tool-grinding radius used was 25.3 mm to obtain the curve profile shown for the 8 mm film roller. The tool was made from the un-ground end of a 0.4-inch HSS lathe tool. The tool side edges were also ground to provide a cutting edge and relief. The tool enabled the shoulders and curve of the roller to be made in one operation. Photograph 21 shows the crude method I used to grind the form tool to get the desired tool curvature. The tool was held in a small machine vice, the vice hold down slot provided the bearing against the fulcrum peg about which the vice was then rotated. The first tool rotation should only remove the corners, then the tool is advanced in the vice and ground again to form more of the arc and the cycle repeated until a continuous arc is ground across the end of the tool. The curvature of the grinding wheel provides sufficient relief below the cutting edge. The tool side edges were then ground to provide a cutting edge and relief. The 25.3 mm grinding radius was measured along the top face of the tool to the vertical mid point of the fulcrum peg
