Hi there,
Most of the time I use plastic/wood inserts/screws for my soft parts (polymers, aluminium), but at times it can be useful to have a metric thread directly in the 3D printed part.
My gut feeling is that it would be better to just print a hole the right size and tap afterwards, especially for smaller threads (<M4 ?)
What is your experience with actually tapping the part VS printing the thread directly, both for smaller and bigger sized threads ?
Looking forward for your answers
John
I printed thread in high temp resin yesterday for a pressure port. Worked out great. For smaller than M4 I’d print the core diameter and tap it. It’s not so difficult in this acrylic like material.
@JasonLivingston did a writeup about this a few years ago, which you may find informative:
Thanks for the answer Matt, in fact reading Jason’s article was what pushed me into writing this post. He does write about printing threads but not about tapping them afterwards, I should have specified that in the original post 
Hi, thanks for sharing your experience ! I see we share the same gut feeling about this.
I plan to make a few test in a single part with small(ish) threads, both printed and tapped and will try to make some measurements. In the meantime I’m wondering of others like you have experience with this stuff.
You have to be super careful starting the tap but printing the threads then cleaning up with a tap works well. You just have to be gentle.
I would recommend a full post cure before cleaning the threads up. Also as stated above anything below about M4 is going to be a challenge to print and won’t be very functional.
I’ve used some posts with a hole drilled for M3 screws and it worked just fine
The original post actually mentioned printing threads and then chasing with a tap, but the updated guide focused on the best ways to connect printed parts using screws and I found a lot of better techniques than printing the threads directly. If you do want to print threads, larger threads work better than smaller and it helps to fully post-cure your parts before tapping (as @FredB also suggests). The printed threads will always be more delicate than the metal on metal thread options recommended in our guide and won’t even hold as well as wood screws in Tough resin.
Tapping small 4-40 threads is simple (on clear resin) and actually the screws will self tap. Larger diameters are trickier. I tapped a few 1/4-20 threads on the black resin and it ends up cracking a bit on the exit point if the material isn’t even. Will try printing the thread and following with a tap.
@waveformer, let us know how it turns out! You might be interested in updating this newer Forum thread (about threads):
Hi, Does increasing the resolution help with getting better threads?
Editing support material gave me defected faces also. Any thoughts on this issue?
I am trying to have the best quality for the threads without tapping because tapping works with small sizes as M5 etc… but I need big sizes so what parameters are important in order to get best thread quality?
I gave some clearance between male and female threads. I am doing experiments at this moment and It would be great to get tips from you guys to reduce experimental time.
Thank you.
I can print threads like the NPT thread on 1/2" electrical conduit connections. no problem.
Smaller threads I print a pilot hole and then carefully tap prior to curing.
But most often, I print a socket that will hold a metal or nylon nut. And sometimes embed the nut permanently by back filling the slot with resin I cure with a pen laser.
I’ve had great success in printing straight holes of the correct size and using self-tapping plastic screws (screws for plastic - not made of plastic) for assembly. I have one model that I’ve printed a couple of times with outside 1"-14 ANSI threads that prints just fine at 100 microns.
I always print slightly undersized holes, then tap.
I also found that I can use nylons screws, and they work great, because they will not easily strip the resin threads like a metal screw would.