Design for 3D-Printing

> Cut threads into printed parts with a thread tap for quick design of low-reuse joints.

I've found wood screws work well for this. The wood screw can cut its own threads without needing to use a tap.

It does put some stress on the part, though. I mostly print in PETG, which is strong enough; but PLA might split if the hole was parallel to the layers.

> A design limitation of threaded inserts is that they are not reliably usable for screws inserted from the back side. During insertion, heat-set inserts often push some molten plastic into the hole beneath them, preventing easy insertion of a screw from the back side.

A trick I sometimes use:

1. Before installing the insert, insert the screw from the back side

2. Screw the insert onto the protruding screw

3. Use a soldering iron to install the insert+screw together into the plastic

Because the screw is filling the hole, the molten plastic can't block the hole. Instead, the molten plastic forms itself around the screw, and it acts like a Nyloc nut.

If you don’t gave a tap handy you can quickly “heat-set” threads in a part. Print the hole slightly undersized (I usually go 0.2-0.4mm under for M3-M4 size screws) so it takes some effort to screw in, then quickly screw the screw all the way in with a cordless drill. Friction should heat it up enough to melt the plastic and form it round the screw. Wait until cool before removing the screw. :)

In my experience even small machine screws (M3) can cut their own threads into a properly sized hole, and function well enough for a small number of re-assembly. That said, I'm rarely designing for portability, I just find the right sized hole for my printer by printing some test prints.

Plastic-cutting thread screws can also be great for this; the threads have higher pitch and wide spacing, but aren't as deep as a wood screw. The <1000-pack selection on Small Parts / Amazon can be slim, but in the last year Bambu started selling small packs for reasonable prices.