Today I did a bit of experimenting with using a lathe as a metal shaper.
A lathe rotates a piece of material, and shoves a basically static tool into it to cut away unwanted material. A mill rotates a tool, and shoves it into a basically static piece of material, to cut it away.
A shaper doesn't rotate anything. It traverses a tool across a workpiece. It's like an unrolled lathe.
It's possible to make anything with a linear travel into a shaper, so today I decided to try it with the lathe.
Pity the pictures aren't more in focus.
I ground a bit of tool steel with a profile like a rectangular keyway, and mounted it sideways on the lathe toolpost. That way, as I move the carriage left and right, the tool slowly peels off layers of metal on a piece of metal clamped in the chuck. I engaged a pin on the chuck so it can't rotate.
The best setup for this, I learned, was with the edge of the tool that's removing the material more or less in line with the point at which everything's attached to the carriage. If the cutting edge is closer to the workpiece than the attach point is, the edge tends to cut more deeply as it deflects, meaning a positive feedback that leads to very high stress. Oppositely, if the cutting edge is further out than the attach point, it bends out of the cut, which is good because it doesn't bind but it does tend to cut a ramp rather than a slot unless I take like a dozen cuts at each depth.
As a result, after a couple of cuts I ended up doing the rest of the cutting on the backside of the lathe, because the offset of the boring bar I'm using is towards the back of the lathe.
I could advance about 0.003 inches per cut, peeling off big curls, taking three or four cuts per advance, and it did a fine job.
The lathe gears have two keyways, one on each side, and now I can cut something that can fit them.
One thing a shaper can do, that is difficult to do any other way in a home workshop, is cut an internal spline or gear. That's one of the eventual aims of this project.