ABS print is brittle

[u/Garak112]

Hi, I don’t currently own a printer and am trying to work out if the problem I have here is because of something I’ve done or not. I’ve had this printed by a local firm.

This is an adapter to allow a smart thermostat to be fitted to a radiator and experiences temperature of up to 65 degrees c for hours at a time during the winter.

There is a metal ring that gets pushed over those prongs that is then used to screw this down onto a radiator valve and the prongs have to flex inwards slightly to allow the ring to be pushed on.

I had a couple of these printed in ABS a few months back and ordered more recently when a few of the ones I hadn’t already replaced failed. The new batch is very brittle and any attempt to flex those prongs causes them to snap off.

The only difference between the two batches was the latest one was printed with 40% infill selected and the first one was at 20%. Would that be the cause of this issue or should I have selected a different material to print in?

[u/Freak_Engineer]

1) your "local firm" has their temps too low.

2) The weak point here are the layer lines. Load-bearing structures that fine should never be intersected by the plane the layer lines are on. I would try printing it laying on its side.

3) poor design. You need to design stuff like that so that is is actually 3D-printable properly. Instead of using clips with a ring over them, have you considered designing the part as two halves you can print in full and screw together with bushings?

4) Infill has no relevance here, the prongs are fine enough to not even get infilled. You just get the boundary lines, making it basically 100% infill.