pic: 968 - Even more unfinished parts!!

[Alan Ing]

This past year, I made a gear hobbing attachment for a generic bridgeport milling machine. So far we have cut type 35 and type 25 aluminum sprockets from 6061 and 7068 as well as cut a few 20 DP and 32 DP gears in both steel and aluminum.

Unlike an indexing method where you cut one tooth at a time and reindex, a hobber spins the gear blank and proceeds to cut all the teeth as they revolve under the cutter.

Sorry, I don't know how to post pictures, but there are a couple on our website showing the hobbing attachment making a 25 DP cluster sprocket and a type 35 sprocket.

http://www.mckinleyrobotics.org/2007...es/0120-01.jpg

http://www.mckinleyrobotics.org/2007...es/0119-02.jpg

http://www.mckinleyrobotics.org/2007...es/0118-06.jpg

Basically, I put an optical encoder on the spindle of the mill which runs through an adjustable divider circuit which in turn provides step and direction pulses to a servo driver which turns the gear/sprocket blank at the exact speed to cut whatever number of teeth we want. The gear or spocket blank needs to turn at the spindle speed divided by the number of teeth you want to cut. Whats nice about this set up is that I can stop the mill midway, check measurements and start it up again without losing sync.

Unfortunately the pictures do not show the servo drive on the 5c collet spindle. Maybe the next time I set it up we will take some better pictures.

If there is enough interest, I might write up a white paper or something at the end of the season.