One important thing to consider is the yield stress present in the material. If you're 3d printing something, it's probably either PLA or ABS plastic. These are layered extrusions that are melted together layer-by-layer as a thermoplastic. Why does this matter? Residual stress. Residual stress is the internal stress present in a part while under no load (just sitting there). Residual stress eats up your total allowable stress and results in a part that can take less loading before it breaks.
In extrusion processes, you're having high temperatures and a rapid thermal cycle present at the nozzle outlet. This causes both residual stress formation as well as potential part deformation due to the rapid expansion and contraction present from heating/cooling. This process is repeated over and over again over a period of time. In injection molded parts, you have one thermal cycle that affects the part at approximately the same time.
Ultimately, this means that 3d printed parts are generally less durable. Picking a different material can help because you get a higher overall yield point. ULTEM 9085 is my personal favorite for semi-durable 3d printed parts but it's pretty expensive. It runs about 350$ a roll for a 25,000$ printer setup.
If you keep going up the scale, you go into laser sintered, laser melt, and electron beam alloy-powder technology. These are truly durable parts that can be used in permanent applications. The cost of the printer is beyond most businesses that aren't serious. Desktop-style printers run about 35k with industrial-quality printers starting around 250k. On the bright side, individual prints are relatively cheap due to the low cost of metal powder (though it varies depending on additives).
Now bringing it back to hobby-scale print jobs, you're probably fine to 3d print gears for something thats non-critical and you expect to break eventually. The real question is what load you're expecting to drive with this. If you're trying to make a reduction gear to move a toy car, you're probably fine. If you're trying to make a gearbox to drive a backyard satellite telescope, you're going to strip the gears pretty fast more than likely. Those cyclical stresses are going to break it eventually.
All that being said, I highly recommend McMaster Carr
www.mcmcaster.com for purchasing mass-produced, casted parts. It's like DigiKey for mechanical parts.
, thanks so much for the amazingly detailed answer! I'd never even heard of alloy-powder technology. One thing I'd like to very quickly point out, we have a very strict policy about being an independent forum and community here, so in addition to your fine recommendation of mcmcaster.com (which actually you seem to have mispelled the URL for, we'll correct it) could you please mention any affiliate or lack of affiliation? This is a really important point with blogspam, as one of the
primary, driving forces behind the existence of this forum is to be independent and not belong to any particular supplier or even community (Arduino, Raspberry Pi, etc)
It's just about curious people like me and you. So while recommendations like the above are extremely welcome, we
need to know about any affiliation. (I personally think that one of the worst aspects of the Internet in 2016 is a lack of transparency in affiliations, which makes it go from the best, most informative source where you can get detailed information in milliseconds (under 1000 milliseconds) to one of the worst sources of information where you cannot trust any recommendation, and you are far better asking any of your friends.)
So on this point we have to be super-clear. (People are allowed to have affiliations and give even glowing reviews, but they have to say it if this is the case. They have to be here to be independent and participate in the community, sharing and building things together
...)
Okay, whew. Turning back to the meat of your response: I googled "alloy-powder 3d print" but didn't find easy printing services. Is this something where you can order a print in a low quantity (like quantity of 1) from a printing service? Or, how does it work?
here's my search, but I didn't see any prices or get the sense that I could "just order" something. How much are we talking about?
Since we're talking I'd love to get a bit more of your knowledge
And maybe share what I'm doing.
As far as knowledge, I have never used CAD software and have a basic question. You mention 'stresses'. Does CAD software actually model stresses or motions? After I design some gears, could I 'watch them turn' and somehow visualize the stresses? Or does any software do that?
If it's like Blender (just 3D meshes, not really some sort of "mechanical modelling") then I guess it's impossible to know.
Basically what I'm asking is:
- Suppose I design a gearbox that can't turn (e.g. this funny picture:
Which this
blog post makes fun of.(Because they can't turn.)
Could I somehow see this in CAD software? (By applying a turning force to one and either see what happens or watch the stress go through the system?)
Or do I just have to "visualize" whatever I'm doing?
Finally, as far as sharing what I'm doing, I'd like to design a kind of small pawl-and-ratchet solution that arrests motion in two directions,like this:
But what makes it harder is that I am considering making the pawls (the purple arms, which would be attached at a location you can't see) kind of flexible. Then with an electromagnet I can draw them back to unlock the gear, or release them to have them spring into splace.
What do you think about this?
Thanks so much for your detailed response, by the way - I really appreciate it! I hope you can stay around and be as helpful as you have been
It's just about curious people like me and you. So while recommendations like the above are extremely welcome, we need to know about any affiliation. (I personally think that one of the worst aspects of the Internet in 2016 is a lack of transparency in affiliations, which makes it go from the best, most informative source where you can get detailed information in milliseconds (under 1000 milliseconds) to one of the worst sources of information where you cannot trust any recommendation, and you are far better asking any of your friends.)
