Bull Gears - Part 1

The bull gears were the next big things that I tackled. I knew that this would be a very time consuming machining operation and that once set up could basically run on its own while I worked on other component parts for the Tractor. The bull gears have a 16” pitch diameter. My lathe will only swing a 13” diameter. So this is where I put the 55 year old Kearney and Trecker (K&T) universal horizontal milling machine to good use. When I purchased the machine several years ago, I was very fortunate to get all the attachments that went along with the machine, especially the powered rotary table. I basically turned the machine into a horizontal lathe. Instead of a tool bit, I used end mills to do the cutting. The attached pictures show some of the various processes involved. The rotary table is powered via the table power feed through a special gear box mounted on the end of the table. I made a fixture that looks somewhat like a 4-jaw chuck and mounted that to the rotary table. Before mounting the casting I found the center of the bull gear in relationship to the spokes. This is where the excess material on the OD did come into play. The gear blank was not cast symmetrically, so some concessions had to be made. I made sure one surface was relatively flat for a reference surface. Once the center was found, a hole was drilled and reamed 0.501” diameter for a locating dowel pin. I had a similar hole in my fixture that was located on the center lines of the rotary table. The gear blank was place in the fixture over the locating pin and clamped in place by the four bolts like using a four-jaw chuck. As the bolts were tighten, the locating pin was pulled in and out to make sure the gear blank was not favoring anyone particular direction in the fixture.

I proceeded to use a 2” diameter roughing end mill to remove the excess material within 0.050”- 0.060” of the finished dimensions. A ball end mill was used to make a nice fillet towards the face of the gear. A standard 4-flute end mill was used to produce the final finished surface. One picture shows how much material had to be removed from the spokes. The gear blank started out at 57 pounds. When all the machining was done, it weighs a mere 26 pounds. Why the gear blanks were cast with so much excess material, I do not know.

 

In any case, while the K&T was doing its thing, I was able to work on the front and rear wheel hubs.