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Hi

I have been creating an orrery (planetary mechanised model) using gearotics motion to generate the gears, cnc milling machine to make the metal parts and now my lovely new Rostock Max V2 to print the parts I generate in 123D.

I have been making the centre gears and had already printed them in PLA on a Ultimaker 2 and they were good, but I needed a bigger hub to manage the torque. I re designed the gears in 123D and started to print them and I had ABS in the hotend so I thought I would print with ABS. The advantage was that I could heat up M3 thread inserts with my soldering iron and slide them into the 4mm holes in the hubs and this works very well. I have been reading google posts on ABS vs PLA even watching Youtube videos on the models being destructed and I am somewhat confused. The general wisdom seems to be that unless you are making parts that can withstand higher temperature, to go for PLA. (there is a lot of stuff on environmentally friendly but I am not excited by this)

So after a long preamble, my findings are that the ABS gears (these are about 150mm diameter) look nicer, adhere to the bed with the hairspray I have been using, are smoother, have a nice bit of flex to them, enable me to easily insert heated thread inserts, have no blobs or hairs. What are your thoughts.

Sorry if this question has been done to death, I am quite new to 3d Printing, but definitely hooked.

Use the material appropriate for the job. If the flexibility of ABS is not an issue and everything else is working well with it, use it. PLA is stiffer. It also does have a lower melting point so for some higher temp applications may not be usable. You can insert threaded inserts in PLA exactly the same way, I do it all the time.

My understanding has always been that, in an application where wear is an important consideration (like a gear), PLA has a superior wear life, and having sanded both for final fit-up of parts, it is indeed a lot more work with PLA. That said, I generally try to work in at least ABS if its other properties are good enough for the application, as having parts deform in a hot car is not my idea of a swell time.

I'm generally a ABS or nylon guy through and through, but PLA does have vastly superior stiffness. My rule of thumb is...If you want something stiff that won't see high temps, go with PLA. If it needs to be flexible (but still usable) and wear/temperature resistant, go with nylon. Pretty much everything else, ABS.

And like mhackney said, heatset inserts work fine on ABS or PLA.

I generally prefer ABS for mechanical parts unless I need the hardness of PLA. If you use ABS though I find you have to print it in the 240+ range to get good layer adhesion.
If you have a press fit and it's a little tight in PLA it tends to delaminate or crack, ABS has enough "flex" it tends not to.

What do you need most in the gear system?

Stiffness?
Strength?
Wear resistance?
Temperature resistance?


If you have a CNC mill, you might consider milling a circular disc with a few holes near the edges, then printing a gear-ring that slides over the outside and is held in place by the holes. It gives the best strength and stiffness. Otherwise, focus more on the tooth contacts and optimize them for more contact area. Plastic gears can be made to have no backlash since the plastics we print with are 50-200 times less stiff than steel.