Advice on 3D printed gear

[lesrhorer]

I need a gear for the encoder on an Electronic Lead Screw, and I can't find one the proper size online for a reasonable cost, so I have decided to 3D print the gear in ABS and vapor polish it. The torque in the encoder will be tiny, so strength should not be an issue, even at 3000 RPM - the maximum speed of the lathe.

First of all, does anyone feel there is a better solution? I thought of Nylon, but that is not an option with my vendor.

Secondly, I am concerned about the set screw. ABS does not have the best layer adhesion, and threading it can produce poor results. A brass insert can produce great results, especially when the screw tends to set the insert deeper into the part. In this case, however, the force of the screw will tend to push an insert out of the plastic, producing a likely failure. I thought of drilling and tapping the shaft of the encoder, rather than the gear hub, but I don't much like that idea. A roll pin might be a better solution, but frankly, I don't like that much, either. I could have it printed in PETG, which has far better layer adhesion, but it won't be as smooth.

The gear is 56 tooth, module 1, 6 mm thick.

 

[KyleG]

I printed a change gear in PETG, and it worked like a charm. If this is just the gear on the encoder, that set screw won’t see much load at all, so I would just tap the plastic. I would also leave the top side of the gear flat, rather than dishing it in like that.

 

[brino]

I have seen brass nuts that you can sink into the 3D printed plastic part with a soldering iron. I have not yet tried them.

Another thought: what about drill and tap the plastic hole for a heli-coil type insert?
Again, I never tried it, but it should give better wear resistance and allow you to tighten/loosen the set screw without damage to the plastic.

Watching. I am very interested to see other suggestions.

Brian

 

[jwmelvin]

Heat set inserts work wonderfully but I’d imagine maintaining concentricity would be challenging at best. Given the low torque requirement, a pressed-in insert seems good. Finding/making an insert with a flat in it is nontrivial, so maybe the insert would omit the flat? I’d probably just screw the grub screw into a slightly undersized hole and see how it works out.

 

[atunguyd]

Another simple solution is to design a slot that is perpendicular to the bolt hole and the exact width of the bolts mating nut. Then slide the nut into that slot and run the bolt through it. The captive nut will perform like a threaded hole

Sent from my SM-S908E using Tapatalk

 

[WobblyHand]

Another possibility is to use timing pulleys instead. I looked into using gears for this application for my version of ELS and went with timing pulleys and a timing belt. In my case, the required gears wouldn't fit in the space needed.

 

[Ulma Doctor]

I have printed PLA gears that have survived. I didn’t use threaded inserts, i just tapped a slightly undersized hole for the retention set screw

This might not be ideal for gears that are changed out continuously, but for intermittent use- I can’t see going to too much trouble for retention.

 

[homebrewed]

An aluminum or steel collar around the hub would do the trick. Drill/tap that and use a set screw long enough to get to the shaft (though your printed hole, of course). That way the plastic only has to withstand the small amount of torque needed to turn the encoder.

 

[lesrhorer]

I printed a change gear in PETG, and it worked like a charm. If this is just the gear on the encoder, that set screw won’t see much load at all, so I would just tap the plastic. I would also leave the top side of the gear flat, rather than dishing it in like that.

Yeah, maybe I am buying disquiet worrying about it.

The bevel features increase strength and reduce mass and cost. I left the bottom flat, so as to eliminate support structures, but the top will not need any.

 

[lesrhorer]

I have seen brass nuts that you can sink into the 3D printed plastic part with a soldering iron. I have not yet tried them.

Another thought: what about drill and tap the plastic hole for a heli-coil type insert?
Again, I never tried it, but it should give better wear resistance and allow you to tighten/loosen the set screw without damage to the plastic.

Watching. I am very interested to see other suggestions.

Brian

I have. They work great, but I have never used them where the screw pushes outward on the insert. I am not sure Helicoil or other manufacturers make inserts that small. Also, a Helicoil insert won't really fix the issue, although it will reduce it somewhat.