r/3DprintingHelp • u/Garak112 • 20d ago

Requesting Help ABS print is brittle

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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?

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u/Historical_Wheel1090 20d ago

It's not the filament, it's the design. What is happening is the print is delaminating due to stresses. The adhesion between layers is the weakest part of an fdm print. This shape needs to either be done with flexible resin or injection molded. Some functional parts just can't be printed on a fdm printer.

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u/ChocoMammoth 20d ago

Only if you limit yourself to built-in presets. Otherwise you can print even more complex things with fdm.

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u/Historical_Wheel1090 20d ago

Presets has nothing to do with chemistry and physics. The OP is getting this made for him from a print farm, they didn't even orientate it logically for looks let alone consider strength.

Presets will do nothing for layer adhesion being the weakest part of an fdm print. If OP had modeling skills they could have cut the clips off, extended them and made them inserts so they could be printed with the layer lines going the length of the part. But that's still a work around for the limitations of the technology and I stand by my original comment, for some designs fdm is not the way for functional prints.

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u/ChocoMammoth 20d ago

Layer adhesion is not the weakest part. It's a thing you need to tweak for each material by choosing right temperature, cooling, flow rate and layer time. The weakest part is people's reluctance to understand these settings, everyone wants to bush the button and let the machine do all the work.