Good morning - I’ve got a lot of experience in my life with vector-based graphic design, this is my first trip into 3D modeling and 3D printing. First simple project was a speaker mount for surround speakers in my den. Printed a test run using a gray generic (hobby lobby) PLA for fit test. Not too surprisingly, I know how to measure, so the fit was fine. Print was solid. (all default Bambu A1 settings BTW).
Next was to print with same generic PLA but black. First run the post that protrudes to hand the speaker on snapped off as soon as I touched it. They are small, quick prints, so I ran another one before bed last night. This morning, I peeled it off the bed and again, the tab/post snapped right off.
I am going to assume my model is flawed. I’m going to try to attached both files (FreeCad and exported STL)…. hoping someone can look at it and say “hey noob, here’s your problem…”
Interesting conundrum. The model as a model is fine but if printing flat the post is a weak point for shearing due to print orientation.
If possible I would change the design for a more robust post or different hanging design option.
If not my next change would be print orientation, but it will still be a weak point depending on how much weight is on it but stronger than a straight shear point in relation to the weight.
Hopefully, some one has better insight. I model for trinkets and toys so don’t have much experience with engineering design.
Thanks for the insight. With two black failures and two gray successes I’m starting to question the filament and the inherent weak point you mentioned.
For now, gonna spray the gray ones black and move forward with some experience.
Yeah, I would be suspect of the Hobby Lobby filament. Your printer is top notch, and you should buy high quality filament as well. As for the design, I would make the hanging pin more of a wedge shape.. Add some meat to the design whilst considering the weight of the speakers and how much you value them…
I second this suggestion. 3d prints are very much “non-isotropic” — they do not have the same properties (e.g. strength) in every direction. Even if it doesn’t snap off initially, you have proved that it is a weak point. That means it will probably break later even printed in the better filament.
Also, even filaments made by the same manufacturer from the same “feed stock” can have very different properties due to the “master batch” they add for color.
I’ve used screws for exactly this purpose — giving strength to a relatively narrow part printed vertically — successfully, including for the handle that I put a lot of weight on, here: Parametric speed handle for machinist vise - #5 by mcdanlj
Here it is with modeled threads for an M3x8 screw:
Another option for 3D printing strength is to print the part at 100% infill with a filament which has the property of allowing an additional melt/cooling cycle, then immerse it in a pan filled with fine salt, then bake that in a spare toaster oven until the plastic melts together becoming an amorphous mass, then allow to cool:
That salt re-melting looks interesting, might try that one day. But wrt the OP’s issue, I often make things where I need more strength than I’ll get from a 3d print (filament or resin) so I design them to include hidden carbon fibre rods to give them that strength. You can find CF easily on ebay etc but CF rods are commonly used for RC model aircraft and, if you have a model shop nearby, there’s a good chance they’ll have stock. It has tremendous shear strength and for a speaker bracket I’d probably use something like 4mm round, making sure I had a 4mm (or, better, a 4.1mm) drill bit to ream the hole after printing. When I glue the rods in place the one thing I DO NOT use is CA (aka superglue). It sets on CF in a nano-second giving you zero work time. I use a type of PVA called super-phatic, also commonly stocked in model shops. This is a lovely, watery-thin glue that is perfect for rod inserts.
