This month's tip is size control on a manual horizontal hobbing machine. On a machine of this type, the size of the finished gear (over pins) is controlled by a lead screw with Acme threads that runs in a bronze nut. There is a locking mechanism for the nut that prevents it from turning after size is set. Too frequently, a operator makes the mistake of trying to adjust size without unlocking the nut. This practice "stretches" the threads in the bronze nut thereby creating backlash in this assembly. It is important to take up this backlash when attempting to adjust the size of the part you are cutting. The best method is to go past the size on the dial going down and then return to the corrected size on the upstroke. The only way of knowing how much you must go past the size is to determine the amount of backlash that exists. This can be determined by common indicator measurements taken without parts or tools in the machine. If you have questions concerning this procedure feel free to contact me at this website.