Some printing tips:
Adjust 'Horizontal expansion' to -0.1 on gears and plates to get a smoother engage.
Reduce flow and/or use horizontal expansion reduction for pins, gears, and maybe scrrews and nuts if you have trouble inserting or screwing parts.
In Cura you can 'shrink' or 'grow' a figure using 'Horizontal expansion' parameter. Most of slicers have this parameter but may be named diferrently.
If gears don't engage well they spread appart when cranked.
If flat guides are too flexible try using more infill or more top/bottom layers.