3D printed gearbox comparison

Opus 5.5 and Fable 5.1 built the same gearbox. On screen, a tie. On the print bed, one of them came out as a single fused brick. Fable is the pricier model and works through every detail. Opus costs less and builds exactly what was asked, nothing more. > SPEC - one gearbox described in a paragraph: housing, shafts, three meshing gears > SOLID - each model outputs the parts as separate watertight bodies, ready to export > SLICE - both files pushed through the same slicer profile with no manual fixes > PRINT - the whole gearbox printed in place as one job, identical filament and heat > TURN - the finished assembly driven by hand to see whether anything actually spins On the monitor the two gearboxes looked interchangeable. Teeth meshed, shafts lined up, nothing intersected. Opus 5.5 modelled every part exactly to size. Exact is the problem: printed plastic swells, and a zero gap becomes a weld. Its gearbox came off the bed as one solid block. Every gear was there, perfectly shaped, and none of them could turn. Fable 5.1 left roughly 0.3 mm of air around each moving face without being told to. Its gearbox spun on the first try. It also chamfered the bottom edges and split the housing so the gears can be serviced later. Neither was in the brief. One model built the drawing. The other built the object the drawing is supposed to become. Opus is the cheaper pick for drafts and blockouts. Fable’s 2.5x premium pays for that 0.3 mm and everything around it. A render forgives everything. A printer forgives nothing, and it never grades on a curve. The two files, the slicer profile and the clearance each model picked are packed into the thread.