Experimenting with 3D Printed Linked Objects

All the experimental models.

After doing a bit of experimenting with #3Dprinting snap-together bracelets, I took on a new challenge to #3Dprint pre-linked objects - that is, objects that are linked at the time of printing. Printing some snap-together bracelets is what really prompted this - I was looking for an alternative design which might print well in metals (through Shapeways, for example), and didn't think snap-together parts would work in metal.

This round of experiments ended up being 6 models. I've outlined each below with my thinking at each stage. All of these designs focus not only on getting a strong-but flexible connection, but also on a structure which would print well the first, and every time on a 3D Printer. That meant parts which build up from the bed at an angle or lay flat. Although most printers can handle some "bridging" (parts which are suspended practically in mid-air across two other parts), I avoided these to make the printing simple, and, frankly, for the design challenge. I also didn't want to have support material to clean up (cut away) after printing. You'll notice in each model that the linkage parts always angled up from the platform, which helps to make sure it can print.

Model 1: Inter-lock

This first experiment was actually quite successful in some ways. The linkage parts of each individual object start out being printed separately from it's parent, but then slowly angle toward the parent object until they connect on the top layers. with just about 0.3mm between the interlocking parts, the printer handled this well and didn't bind the objects together at all. When removed from the bed after printing, the parts moved independently as designed. There was one major flaw - they only moved in one direction - up. there was no flex in the downward direction, since the links were horizontal and restrictive in the vertical direction. This would be an interesting design for links in which you WANT to restrict the motion.

Model 2: Two-Part

After that first experiment, I went back to thinking that independent parts might be better after all - as long as I could come up with a design which made it super simple to put together while still hard to get apart (so linked objects don't fall apart). This first attempt was mostly a complete failure. The parts would link together with lots of twisting effort, but the freedom of motion wasn't there and there was simply too much linkage bulk, and the links were sharp-cornered. I thought it was worth tweaking this one more time to see if it could work...

Model 3: Two-Part Curved

I took the prior model and used curved connectors rather than rigid right angle connectors. This one was super simple to connect, but also way too simple to take apart. The links were also much less likely to injure people with the curved smooth links, but that wasn't enough benefit to keep going (but a lesson for later). There's something interesting here for another whole set of experiments - but I also realized I went far afield of my initial goal - linked parts. I really didn't want independent parts that had to be connected. Back to the drawing board (literally).

Model 4: Interlock Curved

I took the idea from Model 1 and tweaked it to see if it could be made more flexible. This one has more of a chain-like feel, but with multiple connection points - sort of like a double chain. The linkage parts are oval shaped in an attempt to keep them more flat than circles would be. This unfortunately restricted the vertical movement more than I had hoped, but it was workable - and the horizontal "bend" (laterally to the left and right) was appropriately restricted. This was a good design for things like bracelets, which you want to bend vertically to wrap around your wrist but don't need/want them flexing laterally too much. A little tweaking on this one would yield a great result, but I wanted to try other basic designs which were less complex.

Model 5: Loose Link

To get a much more flexible, chain-like connection, I tried a single link design. The concept of avoiding bridging, and using angles to make printing more straightforward, very clearly influenced this design. This one was quite successful - gave me a very strong link and printed without binding at all. The main downside on this design was the "stickiness" of the right angles in the link. While the parts move freely as a chain would, the edges are quite sharp, a bit bulky, and they tend to get stuck in each other's hard corners and don't move as smoothly as desired. Fixing that main flaw was the focus of the next design.

Model 6: Loose Link Curved

This final model was an adaptation of the prior "Loose Link" model, but with two main changes. First, I curved all the angles - using the "Fillet" feature in Autodesk 123D Design to soften every sharp angle into a curve on both the vertical and horizontal loops. Second, I simplified the horizontal loop to start angling up directly at the base of the object rather than first coming out flat on both sides. You can see this clearly if you compare the images of the models from the prior model and this one below.

You can probably tell that all these models above are simply tests and not actually useful - but I expect to use that final model as a method to link parts for kids crafts, jewelry and other models.
If you want that final model in .STL or .123D format, or any of the other experimental models, ping me on twitter!