I’m trying to print a ball joint in one pass, yet still have the parts movable.
I’m printing a model of a mech, which has a ball & socket hip joint (see image below).
The obvious way, would be to print the socket piece in 2 halves, and the ball separate, then glue the two halves after I put the ball inside.
But I’d like to try to print them as one piece, with the ball inside the socket, and with just enough clearance between the parts, that they don’t stick together.
Question: what is the minimum gap I need to leave between the ball and socket, so they print as separate parts (not touching), yet it’s still a relatively tight fit (not sloppy)
Not sure if you can clean the socket enough without a substantial effort in cleaning the uncured resin out. Educated guess try .01"?
FL’s design guide states to use a minimum of 0.5mm or about 0.02".
I tried something similar with a hinge but without success. The play between the parts was something like 0.2mm. Resin between the two parts was cured. Changing the gap to 0.5mm made it successful.
Something with that small of a tolerance wouldn’t work because the laser would cure the material between the parts since the laser will cure a bit extra on the underside of parts.
I think I wasted about 150ml or more trying to do this, but it just doesn’t work. It should in theory, but not in practice. I even oriented the pats so they both print with their own supports (there are no interior supports touching between parts,
I started with a gap of .3mm, then moved to .5, .75, 1mm. When I got to 1.25mm, the part still required some force to break it apart, and the part that is the socket outer shell cracked. At 1.5mm, the parts could move, but the surface was terrible and the gap way too visible.
So I eventually gave up on this idea, and ended up printing the socket in 2 halves.
Well yes, you can only print this design if it is orientate so that there are no supports between the ball and socket.
Like I said, it’s because as it prints the underside of a print will cure material that’s stuck there, so the underside of the ball will cure extra material that’s trapped between it and the socket and would require a large gap for it not to cure that far.
If I was going to try to print these in place I would rotate the part so the ball is vertical and the socket is horizontal. You need to have all layers supported and that’s impossible with the socket vertical.
So, with the socket vertical and a fairly decent gap it should work. Remember they recommend a 0.5mm gap between parts. I would bet that can be a little smaller with grey or black resin.
This was exactly what I tried, I had the the ball shaft oriented vertically, and the upper leg socket was horizontal, I also tried a few other angles where the ball and socket are basically independent, and there is no support between them, yet, in all cases, the 2 parts were fused together.
Only when the gap reached about 1.25mm did the parts separate, but even then, the surface quality was bad, and the joint movement was very rough, so eventually I had to cut my loses and just split the piece. That worked just fine.
The 0.5mm gap is likely to be a vertical gap
Here is the layout I used that actually worked, but only after I reduced the diameter of the ball to increase the gap. The quality of the surfaces on the ball and the socket that faced each other was pretty bad.
Could you post up the STL? I’m interested in trying to print it on a FORM 2
Unfortunately, the STL is way to large to upload here (49MB).
I’ll see if I can reduce it
I’d love to play with this model too. Please let us know if you find a place to host it.
Here is a link to the file. This has been reduced from the original 24MB, but it should still be quite usable for testing
Ball & Socket Joint test file
THis is hosted on my Dropbox account. Let me know if you have problems downloading it.