That is where the helix angle comes into play.
Just a lead screw will put out tremendous force without the worm drive involved.
The greater the diameter of the treadled shaft the less the helix angle will be thus making the inclined plane less on the treads.
Making it easier to turn and create more force.
There are two drive shafts on my lathe.
One is the lead screw and the other is a feed screw.
The Lead screw is 8 threads per inch with a half nut.
This is used for cutting threads.
The feed screw uses a worm drive and the worm runs on a shaft with a key slot.
It turns the worm wheel that turns gears the run on a rack by way of a pinion gear.
It is for very fine feed.
If anything I would need to step up the ratio of the screw drive not slow it down.
Like a worm drive on a fishing reel works but not that drastic and it wouldn't be practical.
It would be expensive.
To give an example my sausage stuffier used miter gears and a so called lead screw.
It takes forever to move the thing up and down.
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