Has anyone had experience with tapping PLA for screw threads? I’m making some tools that use a removable needle needing to be held in place by a set screw. I have found some threaded inserts designed for plastic but I was also curious about tapping the PLA itself.
Many people I have noticed will simply have a hole and use machine screws to join the parts. They will force the screw in letting it cut its own threads. I often model the threads in cad and then use a tap to “clean” them up a bit but do not run the tap full depth so there is still some cutting action by the screw when it goes in.
I find direct threading is fine for “one time” assembly as long as you don’t try to over tighten the screw. Remember we are dealing with plastic and not steel. For multiple insertions, the threads quickly wear and loose their strength. In that case, assembly is done with either nuts preferably inserted into the part (looks better) or use heated inserts pushed into the holes. Biggest caution with the inserts is to get them straight or you will have problems. (Voice of experience here). Also, if doing plastic threads, it is advisable to make the threads longer than you would for a normal metal nut to help give support.
Most of my experience has been in 3 and 4mm sizes.
HTH
Thanks for your insights. I think I will go with the threaded inserts and press fit them. I may have to try designing some cad threads sometime, just for the learning experience.
I recently did exactly what you’re talking about. I’ll post some photos later, but it involved tapping some PLA for M5 metal screws, as well as using a couple of PLA bolts into metal T nuts. All are working well so far. Is it ideal? No, but it’s what I had at hand…
I’ll be interested to see some pics. Thanks!
I insert metal nuts or threaded spacers. Works perfectly for me!
Do you pause the build so you can insert the nuts, then print over the edges to secure the nut(s) in place? Pictures man, or it didn’t happen ?
Interesting idea…I design a hole to the same spec as if I were drilling it then press fit the threaded insert. Took a couple of tries but I have it nailed down now!
It is very easy to apply this trick into your printed parts. You must consider the physial space between printed and metal wall so the nut will slide easily into the printed pocket.
0.2mm offset from the nut perimeter is ok. Your printer accuracy should be tight to work the trick. From the side you insert the bolt/screw, must be at least 5.0mm to provide strenght on the screwed part. Playing with this trick, you’ll find many other new tricks that will work for you! The attached pictures will help you get the the idea.
In your slicer ,check the last layer before the print over layer that fills the “gap” for your insert and pause printing just before changing the filling layer and insert the nust. Then restart to continue printing.
Exactly! I’ve heard of people using a pause in order to put a magnet inside. The whole concept of embedding things is a really cool advantage of 3D printing, at least I think so. I’m considering using it to add some bottom weight to some objects, to help them stay upright and give them some heft so they stay put better. Not sure what I should use; perhaps some scrap metal, or maybe some cement that could be poured in around infill and then set inside the print.
The applications are endless, but the idea is just one! 
Be aware that PLA will deform under pressure over time. Use of embedded or recessed nuts, or heated metal screw inserts can help. Stefan has an excellent series of videos on his CNC Kitchen YouTube channel on this topic. Tapped threads can hold, but do test for longevity.
For mechanical parts that accept stress, must never use PLA or ABS. PETG, HIPS, CARBON nylon and such , are moslty wellcome!