Posted by Jim Pollock on January 30, 2010 at 22:26:05:
I have posted before about my #12 hobber having trouble making a smooth finish on gear teeth. I have done eveything that was suggested before but the machine continues to make rough looking teeth.
Here is how I have it set up. I am cutting a 37 tooth 7dp spur gear. I have a 30 tooth change gear on the right shaft and a 37 tooth gear on the left shaft. I have a 60 tooth gear as an idler on the swing arm. I am using a single start right handed hob. The cutter shaft is swung 3 degrees and 5 minutes in a clockwise direction when looking from the top. The hob is rotating so that the top of the hob is going toward the work spindle and the gear that I am cutting is rotating counter clockwise when viewed from the tail stock end. I am feeding toward the work spindle at .032" per revolution of the gear. I have not tried to climb hob.I am getting the proper number of teeth but they are very rough. I have tried to take heavy cuts and light cuts and so far a cut of .015 has produced the best finish. The finish looks great as the hob is starting into the gear but as soon as hob starts cutting full depth it starts to make very rough teeth like something is loose. I can't get more than .001 play in any spindle and about the same backlast in the work spindle.
The only problem with the hobber that I can see is that the 60 tooth idler change has a lot of wear in its bore. I can actually see it rise and fall slightly as it rotates while hobbing a gear. Would this cause the machine to hob a rough tooth?