The Model Gatling gun that I built needed two cylindrical cams. They are the things that push the bolts in and out to load and extract the cartridges as the drum is rotated. The cam surfaces were helical in nature so the helical attachment that I posted a picture of yesterday was a natural. Shown here is cylinder chucked in the device. A layout has been made on the part and pilot entry holes drilled. An end mill was used to do the cutting. The picture shows a pointer chucked in the collet while I ran through a trial run.
The cam surface ran circumferential for a ways, then a right hand helix for a ways, then circumferential for a ways, then left hand helix back to the starting place. With the reversing gears that had been built into the fixture it was "A piece of cake". Without the fixture they would probably have had to be filed out by hand.
Here is a picture of the finished cams about ready to be installed in the gun.
And here is a picture of the Model Gatling after it was finished. It is a 1/3rd size model. It is functional, and chambered for .22 shorts, which by the way are actually oversize for the 1/3 scale. But that is the smallest commercially available bullets that I know of. I have a good friend named Paul that lives in the Salt Lake area that has, over the years, built several hand crank machine guns. Not all were Gatling's. For some of his, he went all the way, and made scale size center fire cartridges. Even making them in quantity he had over $5 labor in each cartridge. Not very cost effective, but they sure are cute.