08/07/00
Today I began to make the large 180-tooth greatwheel. A blank was made from 4-inch-wide 1/8" leaded brass. A hole less than 1/4" was made in the center of the square of brass, then reamed with a 1/4" reamer -- this makes the hole more exact. The edges of the blank were ground off to make a circle.
It is essential that the edge of the brass be concentric with the Sherline rotary table, so after the blank was mounted on the bolt in the middle of the rotary table, it was trued with an end mill.
Then the edge of the blank is blued with Dykem. This makes it possible to set the flycutter so that there is only a tiny "land" (origial surface) on the end of each tooth when the teeth are cut. This means that the diameter of the wheel will not lessen when the wheel is cut. The land is also a good clue to wheel cutting "health" as the process procedes. Watch the land -- should it change in size as wheel cutting procedes, it's a good indication that the wheel has slipped while machining, is out-of-round, or an indexing problem has surfaced.
As is typical with making clocks, problems arise. This time the wheel was too low for the milling cutter to make a full cut through the tooth, so I had to make a filler from 1 x 2 inch aluminum to raise the Sherline rotary table to sufficient height.
Then, as I was cutting teeth, I saw that the teeth were being bent to one side by the cutter -- it had become dull by an accidental encounter with the hardened Sherline rotary table and had its edge ruined.
You often have to redo when making clocks. It's no fun, but it's part of the process.
Nex time, I will mill off the row of ruined teeth. This will make the blank smaller, and require the use of a smaller-tooth gear cutter. Or perhaps, I'll just make another blank.
Today's links:
Bluing the mainwheel edge
Truing the blank edge with an endmill.