Printing Functional Machine Screw Threads with Carbon

Hello all,

Last year I discovered that any carbon-filled material allows one to print parts with machine screw threads that are usable. It occurred to me that this might not be common knowledge.

Actually, I can't believe how well it works. I've successfully incorporated the technique on most of my recent projects with thread sizes as small as M2.5 when oriented vertically on the build plate and as small as M4 for horizontal holes. In general, the threads are strong enough that I can tighten a screw as tight as I can by hand when grasping the smaller leg of a hex key, and can usually go a bit further tightening with the long leg of a hex key. It's pretty amazing... a stainless screw will tighten to a squeak.

I understand this might be unbelievable to some, so here's an STL of a test article with two M5 holes in it if anyone wants a quick way to try it: [www.lightsmithscientific.com]

The build orientation is important as I use different thread geometry for vertical and for horizontal holes. The filleted edges indicate the X-Y plane.

Here's a photo of a part that makes use of it: [lightsmithscientific.com]

I incorporate the thread geometry into my models by keeping a library of cylinders with just the threads in them, which I call "thread features" in my brain, and the OD of these cylinders is the same as the clearance hole diameter for that thread, which is a convenience. The parts that will get the threads just have clearance holes modeled where needed, and then I add the thread features in an assembly. From that I generate the STL, and run it through the Netfabb fixer service to heal the boundaries.

I'm curious to hear if anyone else has played with this.

~Justine

Edited 1 time(s). Last edit at 10/13/2017 09:44AM by justine.haupt.

That's nice work. I often screw into plastic without heat pressed nuts or the IMO much nicer brass inserts but usually I just print the hole 0.2mm smaller for m3 for example and then self tap into the plastic. Printing a thread isn't something I'd thought to do but then I haven't tried carbon filled filament.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I have found PET based nGen prints threads well... My last project was some legs for a desk organiser, and the bases of each foot had a thread and nut to adjust the height of the legs.