I found myself in need of making my own gears. Either the stock gears available didn’t have the proper dimensions or they were just way too expensive. Making one’s own gears is a freeing step for a machinist and someone who builds kinetic sculptures. I already had my old bridgeport mill, and I even had a couple sets of involute cutters and an arbor. The main component I needed was a dividing head. I recently acquired one, so I was ready to embark on the adventure of gear cutting!
The first thing I had to do was cut a gear blank. This particular gear is an 80 tooth gear with a diametrical pitch of 12. The gear blank needs to be (n+2)/dp, or 82/12″, or 6.833 inches in my case. I also had to build an arbor to hold the blank tightly. You can see the resulting aluminum blank in the photo above. To the right is my new (to me) dividing head. It’s got a 40:1 turn ratio, so I needed to turn the handle 1/2 a revolution per tooth. I set the brass spider on the mechanism to help me make sure I was landing on the right hole every time.
Once I have it in place, I had to take careful measurements to get the center of the cutter lined up with the center of the gear blank. Once that was done I sent my stops on the power feed so I could let the machine do the work as much as possible.
Because I wasn’t sure about the rigidity of my set up, I decided to make 4 passes per tooth. Gear cutting is all about getting into a rhythm: line up the cutter, turn on power feed, advance the cutter, reverse the feed, advance the cutter, reverse the feed, advance the cutter, reverse the feed, back off the cutter, and advance the tooth on the gear. All of that was taking me about a full minute per tooth. While that might not sound like much, that means that this gear took about an hour and a half of hyper-attention.
The moment of truth… when you dial up the final tooth to cut and it’s exactly where it needs to be. It’s difficult to explain the feeling of relief when that last tooth is complete.
Now to just clean up the swarf.
Gear cutting is definitely a stressful task, but so far I’ve only messed up a couple of gear blanks. Mostly things have gone fairly smoothly. I enjoy designing with a little more freedom, knowing that I can fabricate my own parts if I need to.