T-nut for Skadis board - interference threaded

Update March 29, 2025

Over the last two months, one or two of the t-nuts worked loose on my Skadis board. I increased the interference by 0.05 mm radially on all three intrusions. The new version (T-nut M3 interference threaded (tighter).3mf) still screws on nicely but tightens in a more satisfying way. I recommend you try both the tighter version and the original (T-nut M3 interference threaded.3mf) to see what works for your purpose.

Motivation for Another Remix

The earlier designs from 696178 and ORM are good designs that hold well. However, adding a nut was another way for assembly to be a little fiddly and printing threads for an M3 requires fine layers. A recent alternative is to have the screws cut their own threads by having  interference ridges in the hole. The part is easy to print and has relatively strong threads.

Printing Instructions

The t-nut is a simple print. Print the model with any layer height and without supports or brim. To increase thread stiffness, print at least 3 perimeters.

Background on the Threads

The idea was introduced by Thomas Sanladerer on “Made with Layers”. The main idea is to print a clearance-sized hole with three internal bumps that create a central  clearance region that engages the full threads. It works better than printing threads on small screws and is easier to to print than attempting a threaded hole. A hole sized directly for full thread engagement is also not ideal since the interference area is easy to strip out and hard to drive due to the amount of plastic being displaced.

Adding the “Threads”

Thomas Sanladerer provided an OnShape volume that can be subtracted from your part's volume to create the m3 threads. Beware that if you use that blank and there is an existing hole (such as for remixing a design), first make the hole diameter smaller so the new thread ridges are full-sized.