I have been working on printing some clips with TPU to help close an open bag or what. I don’t like the idea of PLA clips because they seem brittle. So I tried to just make a normal model.
But then I realized that it wouldn’t work. I printed it out and it just simply make a great squishy and had zero power, not even able to hold a pen. So I changed the design to make it more rigid.
It ended up being pretty good but still results are not satisfying. I think the problem here is that real clips go further than the closed position. The clip is still applying force to go further even when it is closed. I don’t see how you could do that with a 3D printer. Any ideas how to do this?
Another problem here is that the TPU can’t really go back to its normal position. That means that if I pull the clip apart it will go 4/5 the way back. Only if you set the “closed” point where it’s still kind of open you could get guaranteed results.
Radius’s will be your friend. In this case, the model here doesn’t have an area of grip. I’d suggest designing the model in it closed (tensioned) form and printing as such which would result when finished and pulled off bed to close on itself.
Right now you’re printing in the resting position which is why it wouldn’t hold onto anything unless it was forced open gaining (tension) against object to hold it.
Other sources show a value of 162MPa for 95A TPU, which is about halfway between a marshmallow and cheddar cheese.
PETG has worked well for me in several models where I need some stiffness and a certain amount of springiness, without the relative brittleness of PLA.
This designer used separate jaws with different gripping surfaces. Inserting the jaws requires spreading the body apart slightly, creating some initial tension “at rest”.
Another option is to use an “over-center” clamping design. At rest or normal position would be the jaws open. As force to close the jaws increases, they suddenly go over center and snap shut. You would only need a small amount of flex in the hinge area. Perhaps a nylon filament or similar would work.
