While not strictly necessary for metric threading on a USA-ian mini-lathe, a 32 tooth gear can produce reasonable approximations, so I printed a pair from a Thingiverse collection:
The model was designed for a slightly different mini-lathe, as it includes a short boss and thinner plate, but it did fit on the shaft:
The gear mesh seemed odd, though, and comparing it with a standard 30 tooth gear and a different printed 32 tooth gear (about which, more later) showed it was definitely not compatible:
Yes, the 32 tooth Thingiverse gear on the right is slightly smaller than the stock 30 tooth gear in the middle.
The larger 32 tooth gear (on the left, above) meshes better:
Both of those trains have a 600 ppm error, so they’re definitely suboptimal compared to the results with a 21 tooth gear in the train.
The real reason you need a 32 tooth gear is for exact 25, 50, and 100 TPI threads with a 1/16 inch leadscrew. I don’t foresee much need for those around here, but you can never have too many change gears …
The Smell of Molten Projects in the Morning 