I completed the mechanical build of the arm this weekend, and am starting the enclosure. The base pieces that go under J1 and receive the motor plugs and the cover pieces for J5 seem to be the only candidates for threaded inserts. No inserts used yet, but the base pieces should be an easy retrofit. The J5 shroud is super tight and lacks sufficient wall thickness for an insert. This part is easy to redesign/replace later on...

I won't get to the cabinet until later in the week and I will see how it goes..

I'm more worried about assembly and disassembly durability. If you use inserts they will not loosen up over time.

Even though I built AL version of this robot but I can suggest you to use threaded hole feature on your cad program (Solidworks has that) I have been doing that for years and no tapping required. All you need to do is

Step-1: Make a regular hole at minor diameter of the threaded hole, then

Step-2: Use threaded hole feature and create visual threads on, then 3D print.

Note: If you use default features and values, hole comes out little bit smaller and you d ended up simply chasing them. But if you make minor diameters around .010-.015 bigger threaded holes come out at perfect size no chasing required. I ve been doing that for years and results are impressively good. Eliminates a lot of work and they are fully functional.

Suggestion: for example, model up test block 1"x"1"0.5" and put couple of 4-40 or 6-32 holes at different minor dia. and find your sweet spot then document it.

see attached photo

I don’t think you have any problem if you know what are you doing. as long as you can make 2 piece of plastic stick together it should be fine. If you facing problem then you just reprint your part and tap it