Any hobbyists using milling robots?

[strantor]

Note that the 3d printing world is full of total baloney.
I've been into it for a while, and people constantly make claims which are physically impossible, regularly, and folks just nod and smile.

I'm not sure what fallacious claims you're referring to. I'm not putting up any defense, just I haven't seen any snake oil for sale.
Last time I read about hobby 3D metal printing they had some lasers pointed at metal dust, and were fusing it together. Didn't look earth shattering, and isn't what I'd call "3D printing" but there was some progress.

I can maybe relate, but what I've seen is more a general lack of knowledge and information than fabrication of information. Maybe that has improved (or gotten worse, if that's what you're describing).

I initially started down this 3D printing and machining road in pursuit of making DIY prosthetic limbs. I wanted to make a hand for my father who is an amputee. I tried to find out before purchasing a 3D printer if 3D printed parts are strong enough to make a viable prosthetic. Nobody could give me a straight answer. I was appalled to find that at that time (2013) there was no standardized strength test to compare different polymers and processes. So I just jumped in and bought one, developed my own standardized test, and started to compare various polymers available. I tried to spread the word about my test and see if people could beat my numbers; maybe it would reveal common traits of good processes. Nobody took the bait. Nobody seemed to care. Everyone seemed content to print out a chess rook, smash it with a hammer or run it over with a car, and call it ambiguously "strong." Not good enough for me.

Ultimately I determined that 3D extruded polymer printing process cannot produce a viable prosthetic. I check back in occasionally to see what advancements have been made, but but so far I have not seen anything promising enough to give it another shot. There are some new polymers out there but I haven't seen them subjected to scientific testing that would indicate they have any better layer-layer bonding than anything else. Apparently still nobody cares about this, and for the life of me I can't figure out why!

For now I am convinced the only way to make dimensionally stable parts is to machine them out of solids.

 

[Metal]

I'm not sure what fallacious claims you're referring to. I'm not putting up any defense, just I haven't seen any snake oil for sale.
Last time I read about hobby 3D metal printing they had some lasers pointed at metal dust, and were fusing it together. Didn't look earth shattering, and isn't what I'd call "3D printing" but there was some progress.

I can maybe relate, but what I've seen is more a general lack of knowledge and information than fabrication of information. Maybe that has improved (or gotten worse, if that's what you're describing).

I initially started down this 3D printing and machining road in pursuit of making DIY prosthetic limbs. I wanted to make a hand for my father who is an amputee. I tried to find out before purchasing a 3D printer if 3D printed parts are strong enough to make a viable prosthetic. Nobody could give me a straight answer. I was appalled to find that at that time (2013) there was no standardized strength test to compare different polymers and processes. So I just jumped in and bought one, developed my own standardized test, and started to compare various polymers available. I tried to spread the word about my test and see if people could beat my numbers; maybe it would reveal common traits of good processes. Nobody took the bait. Nobody seemed to care. Everyone seemed content to print out a chess rook, smash it with a hammer or run it over with a car, and call it ambiguously "strong." Not good enough for me.

Ultimately I determined that 3D extruded polymer printing process cannot produce a viable prosthetic. I check back in occasionally to see what advancements have been made, but but so far I have not seen anything promising enough to give it another shot. There are some new polymers out there but I haven't seen them subjected to scientific testing that would indicate they have any better layer-layer bonding than anything else. Apparently still nobody cares about this, and for the life of me I can't figure out why!

For now I am convinced the only way to make dimensionally stable parts is to machine them out of solids.

Yeah that sounds about right

What I was typically talking about was "my printer is accurate to 10 microns because I looped my belts around this thing!" and stuff like that

dimensional stability is a huge problem for printers because the infill patterns all effect the outer layers unpredictably as the plastic cools.

I've made combat robot parts out of taulman alloy910 and it seems very reasonably strong and stable but I never did much testing.

 

[cjtoombs]

I suspect the reason that no one is doing any real engineering (materials testing, etc) is that no one is using them for engineered applications. What I've seen in my industry is using them for fit checks for parts with long lead times and pass around and display models. I've also seen them used a lot by hobbyists for art and small functional products that won't kill someone if they fail. The problem industrially is that for the quantities normally needed for consumer products, injection molding is much, much, much cheaper and faster than 3D printing plastic parts.