I’m almost positive that 1020 should be very close to the same rigidity as 304. I know the risks of rusting, I plan on keeping everything well oiled. Have you noticed much wear with stainless rails? I know that smaller stainless rods wear down very quickly when subject to steel on steel bearings. I’m planning mostly on doing light aluminum work (plates and brackets) and engravings, and if I can get away with it I’d like to be able to make simple molds for resin casting and injection molding. I also need a few relatively large things I need 3d printed (new Z-carriage for my main printer).
The good thing is that since DOM is very cheap, and since I pay the same amount per batch for heat treating up to 50lbs, I could just buy enough steel tubes for whatever configurations would be best for each process, and then harden them all for the same cost.
EDIT: 1020 actually looks more rigid than stainless.