How 3D printed joints work

Next time you’re having trouble explaining how 3D printed joints are made, you can point people to a video http://i-t-w.com/blog/2016/2/17/how-3d-printed-joints-work
Youtube direct link (it’s CC licensed) https://www.youtube.com/watch?v=xkwITEewwuk
We’ve not thought up a good explanation, how do you explain them?

Very nice print quality and video. We’re those done on a TAZ?

The smaller one is the 150% scaled version on the file done on a Mini, in glow in the dark Lulzbot ABS.
The big one is a max scale TAZ 5 .5mm print done in a sample of PLA we received. The internal structure is cleaner with ABS. Here’s a LFS “Geant” Elephant print that got killed by a power glitch (I thought it was plugged into the UPS…)


how much space do you need to leave between the parts in the joint?

I find .7 for perimeters (XY) and 1mm for top and bottom spacing works well for “print-in-place” axle / post designs… like the maker faire robot above. You can get tighter tolerances, but they may not work universally on all machines… for instance if you’re planning to share on thingiverse.

If you are designing for just yourself, try using a multiple of your extrusion width X/Y gap, and a constant .75 to 1mm for Z gap. Start with 1. If its too tight (axle is frozen) try reducing your flow rate / flow multiplier to 5% lower. If joints are still frozen, try going to a multiple of 2 times the extrusion width for the X/Y gap… for Z gap stick with .75 to 1mm.

The Z is a larger gap, because it will be printed without supports. So a single layer height for gap may stick too well with the last layer. Using a multiple of 2 should prevent the layers from sticking together or freezing.

Here’s a print-in-place camera mount that swivels that I made for my TAZ: https://www.thingiverse.com/thing:949219


For round joints like the elephant figurine above, you’ll want a consistant gap all the way around… .75 to 1mm would probably be universally good.

I’m having difficulty printing models like this (eSUN HIPS) - I tried the small model last night.

I’m finding the joints fuse. The problem is, I can’t really tell until the print is complete whether it worked or not (a waste of time/frustrating - esp for bigger models). I guess I keep hoping, they’ll break free.
If they touch at all, I should stop the print?

Also, for the finer bits, I am finding it curls/builds up at corners (or where the head does a 180) or loses adhesion. I imagine a brim for a model like this would seal the joints. Any tips?


I’m guessing my printer needs more dialing in to get the more precise details…
I’ve printed the calibration cubes etc and found they look good - are there any intermediate models someone could recommend to test joints etc?

Try reducing the flow rate to 90-95%. This can make the gaps a little wider.

Stick with a thicker layer height… .3 or .4 with the .5 nozzle.

Don’t print with supports or use minimal sparse supports. This means some overhangs will print in mid-air, but with a thicker layer height and a little cooling the extrusion should “lock” into place with minimal adhesion to the previous layer.

Drop the extrusion temp a degree or two, again to help lock overhangs and minimize adhesion to previous or adjacent layers.

As for smaller objects, shrinking the above will affect gaps and most likely won’t work. I posted a print in place camera mount that swivels. Here’s the object on Thingiverse. Just need to print the first “Tray Mount”. Because of the gap for the aluminum plate, you’ll need supports. Should be a 20min print… the top portion (GoPro mount) should rotate in the end.

YMMV… a lot could affect the print. But as IT-works demonstrated the prints are possible… I’ve successfully printed the makerfare bot and the elephant in the past on the TAZ. Keep at it the “print-in-place” objects can be challenging.