Change lead screw to metric?

[liveaboard]

Change gears are a pain; like you said, greasy and fiddly, spacers and nuts can drive you nuts.
On the other hand, I think there are more possibilities, because you can add other gears [if you can source them].
For me as an amateur, the extra time is no big deal, I only cut threads once or twice a month.
It's wonderful to have that capability; many times I've been able to repair or modify something because I'm able to reproduce the threads.

I found a supplier for metric gears; they have just about anything and not expensive.
But I have to cut the keyway with a [gasp!] file.

[tornitore45]

But I have to cut the keyway with a [gasp!] file.

I have only done it twice in aluminum but consider drilling a small hole to remove most of the metal and then use the lathe as a shaper. Locked Chuck, Tool on the tool post ... in and out advancing the cross slide a couple of thousand at the time.

I am pretty good with files but making a keyway parallel and crisp is not going to happen.

[Harold_V]

Keyways?
What tornitore45 said. It's all too easy to use your lathe. Grind a toolbit that resembles a parting tool, and is the correct width of the desired keyway. Mount it such that it will cut towards the headstock, with the cutting face vertical. Keep in mind that the face end of the tool is the cutting surface, though, not what would usually be the top. Use the carriage to stroke the keyway, taking reasonable cuts, using the cross slide to advance the tool in the cut (his recommendation of a couple thou per pass is spot on). A little positive rake will help the tool cut, but don't go crazy, as it may then hog, making stroking impossible.

H

[liveaboard]

I've done it that way; it worked but it was an awful job.
That was a small tapered bore and I had to use the compound slide, I got blisters even though it was cast iron and cut easily.

The change gear has very little torque on it, and actually the filing went ok.

[tornitore45]

Bummer! You could have used the carriage to make some of the slot depth parallel to the axis and then use the compound for the bottom inclined surface

[Harold_V]

Nice! Too bad about the blisters, but isn't in wonderful that a guy can create a keyslot when options are limited.

H