How durable are 3d printed objects?

[awerby]

I wouldn't ride a motorcycle whose frame was FDM printed in plastic. Hit one of those "bumps in the road" too hard and you're vulture meat. But maybe I'm just over-particular about my personal safety; you can do what you want...

[Ama-fessional Molder]

Frame, no. Subframe, absolutely.

That's why the original intent was to brace it with tubing, so the weight is fully supported by the tubing and the rest is just for looks and holding light weight components in place.

[curious aardvark]

you probably could get away with the petg - but just for cmmon sense I'd still use the aluminium reinforcement.
not worth taking risks with your life :-)

playing with the colorfabb xt/petg this afternoon

[Ama-fessional Molder]

Motorcyclists are stupid though.

[curious aardvark]

Well there is that.

[djprinter]

I print mostly ABS which is plenty strong as long as I pay attention to two things:

Layer adhesion = printing at as high of temp as I can get away with and slightly over extruding.

Design = if I really need strength I'll divide a part in two pieces and print each at a different orientation and then glue the part together, the strength gain is sort of like what you get with plywood which is glued together at alternating grain patterns.

[richardphat]

Well.... why not use 3D print as a sacrificial model. I would love to put carbon fiber tissue on it and resin vacuum it. You won't be able to argue with the results.

[Graham]

A subframe for a motorcycle. I only weigh about 220, add another 10-15 lbs with gear, and then assume there will be bumps in the road.

I still intend to print the bulk of it, just reinforce it with aluminum. It will all be visible, and custom is cool. Plus I need to do up all sorts of brackets and stuff for wires, tail light, various electrical control bits, battery, and all that.

I see no problem just designing it with a channel all the way around to just drop in square aluminum tube from the bottom, then have the printed part just "sit" on top of it.

A couple of observations:
First, if you have a design payload of 250lbs, I think you need to design for 500-750 lbs minimum. That "bump" in the road could easily cause a 2G force making you weigh 500lbs for a moment.
FDM printing is inherently weak in certain directions as it is dependent on the tensile and shear strength of the interlayer bond, which is significantly less than that of most of the materials we use.
Tensile strength along the build's Z axis is almost non existent except for very large areas.
Compression directly along the build's Z axis will perform at or near the material specifications where directly supported, however, the beam strength (i.e. bending resistance between supports) is also reduced due the the weak interlayer bond.
IMO, FDM (at least with our hobby machines) is not suitable or safe for any kind of structural requirements in the ranges you need. It would be fine for enhancing the aesthetic appeal of an otherwise strong and well built aluminum structure that is properly designed to support all the loads.
Graham

[Ama-fessional Molder]

Yeah, that's pretty much what I assumed.

[curious aardvark]

It's the terminator/wolverine principle. Flesh is weak, indestructible interior alloy skeleton - much better :-)