@Mike_Miller The replicator 2x uses Nema 17 motors, just small ones. The acme z axis is more than adequate, as I’ve never had issues with the z and y axes. The x axis design, however, is atrocious. Misumi is incredibly overpriced for anything except for extrusion. You can get decent acme threaded rod at McMaster Carr for cheaper, but you’ll probably be fine with normal threaded rod as you’re not moving fast, nor are you moving much load.
As for the bearings, bronze is fine as long as they remain lubricated. IMHO, they’re much better than the LM8UU bearings I have on my home printer, as the starting friction is much lower than the that of the roller bearings. The only reason I’m sticking with the LM8UU’s on my new design, is that I already own them, and BOM cost equals “hey honey, I spent more money” to my wife.
If you want to use Spectra, @Tim_Rastall 's design is probably the best at meeting your size requirements, but I’ve been leaning toward @Eclsnowman 's core xy design, as I’m fine with using timing belts as they’re dirt cheap on aliexpress.
I didn’t quite follow your requirements though, as you stated that the print bed could move, like in the the Ultimaker, or the printhead could move like in the Mendel 90. I think you meant to reverse that.
I had been hellbent on designing to have absolute minimal mass moving, using a core xy gantry with a Bowden extruder system, but then I realized that I hate my current Bowden system on my home printer, and the direct drive on the Replicator 2X I use at work, while still unreliable, is MUCH MUCH better than my home bowden system.
The fact that the Ultimaker 2 uses a direct drive sealed the deal for me on direct drive extrusion.
If you like the ultimaker/tantillus gantry, then go for the Ingentis. I personally, do not want to add more precision rails than what I already own, so I’m opting to spend the money on cheap pulleys with a core xy.
So now that I’ve bored you with my thought process, I hope that helps in any way in yours. Good luck
