A lathe is pretty straight forward. You get a bit of wood spinning, and then gracefully shove a sharp implement into it.
As it spins, material is removed evenly from around the centre point, and you end up with your turning.
How we get the wood spinning though is the interesting bit. We have a few decisions to make.
Modern lathes have electric motors that turn the work continuously. You turn the thing on and it starts spinning towards you, continuously in the same direction. As long as your tool is touching the wood, it’s cutting.
The most common type of human powered lathe works quite differently. It’s known as a reciprocating lathe. You have a batten on the floor with a bit of string lashed to the end. That bit of string goes up and is tied to a long bendy stick that has one end screwed to the celling. When you push the batten down with your foot, it pulls on the string and bends the stick. When you let your foot off, the stick springs back and pulls the batten up to the start spot. Wrap a bit of wood around the string in the middle, and every time you push down on the batten the wood spins one way, when you release it, it spins the other. Hence the term reciprocating. One spin forward, one spin back, repeat.
As a result, the tool is only cutting on half of the rotations so technically speaking, it’s a lot less efficient. If you want more spins per cycle, then you can increase the length of the batten to give the string more travel.
There is another type of human powered lathe which commonly goes by the name of a treadle lathe. You basically have a pedal that’s is attached to a sod off flywheel, that’s then connected to a driveshaft via a flat belt. The shaft connects to the wood that you want to spin. You get the pedal going, get the flywheel spinning, and your off. You have a continuous rotary lathe that’s human powered.
Whether or not I choose to replicate Roubo’s exact lathe, one thing will be for sure; what I build will be stout. As a result, it would be able to be powered with either method, or if I wanted I could even shoe-horn an electric motor onto it. But I’ve decided that I’m going to go for reciprocating. There’s just such a charm to turnings that come off such lathes, not rough or imprecise but wholesome. Much like the light scallops that are left from a hand plane.
I also love the full body rhythm that they create. Every time you power down you engage the tool, and on the back stroke you back off. It stops the second you stop, it starts the second you start, none of that winding up.
And despite the fact that I would never call myself even remotely experienced at turning, I’ve never found them that inefficient.
On top of all that, a reciprocating lathe is far more simple to build, and more reliable that the treadle lathe.
So that’s half the battle of how to power our lathe decided. Next, it’s pole vs bungee, vs anything else that bends.