Advice on 3D printed gear

[lesrhorer]

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.

I don't follow you. How would concentricity be an issue? What flat? The latter might work,

 

[lesrhorer]

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.

I like that idea! It is extremely simple and inexpensive:

 

[lesrhorer]

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.

No, in my case, timing gears would open up a whole other can of worms. I already replaced the main drive pulleys with timing pulleys, and broaching the pulley was quite an issue. I would rather not go through that again. There is plenty of room on my lathe. Removing the banjo and change gears will leave a lot of unused space for a gear the same size as the gear on the spindle.

 

[jwmelvin]

I don't follow you. How would concentricity be an issue? What flat? The latter might work,

I thought the bore would be defined by the brass insert. So the trick is getting the insert concentric with the gear PD; heat makes that tough, but a fixture could work.

Your model appears to have a flat for the corresponding encoder shaft. I meant only that making a brass insert with that flat could be tough. No need though, just have a screw tighten on the shaft’s flat after the screw extends into the round bore.

 

[WobblyHand]

We all choose our paths. Should you change your mind, I'd offer to broach your timing pulleys. I have a small metric set, 4, 5, 6 & 8mm keyway broaches. I found broaching on a lathe to be possible but difficult. I have a 3T arbor press, so broaching is much easier.

I am installing my own ELS system on my lathe. I wrote my own code for it using a Teensy 4.1. Going to be fun. I'm using a touch panel display rather than fixed buttons.

Yes, need to get the rats nest under control! I will probably design a PCB carrier board before I am done with this. Then there will be hardly any loose wires.

 

[lesrhorer]

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.

This gear should only ever be changed if it wears out. It's not a change gear. It is a gear to drive a rotary encoder. Ignoring acceleration, the torque will only be less than .001 N*m, which is tiny. Change gears can encounter around 1000 times more torque on a small lathe like mine.

 

[lesrhorer]

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.

That is another great idea! It is a little bit more expensive, and just a bit more work, but should provide less of an imbalance than a captive nut. If the captive nut solution provides too much vibration at high speeds, I think I will try it.

 

[lesrhorer]

I thought the bore would be defined by the brass insert. So the trick is getting the insert concentric with the gear PD; heat makes that tough, but a fixture could work.

Your model appears to have a flat for the corresponding encoder shaft. I meant only that making a brass insert with that flat could be tough. No need though, just have a screw tighten on the shaft’s flat after the screw extends into the round bore.

Oh, I see. You mean a metal ring pressed into a well in the gear, coaxial with the gear rotational axis. It's similar to homebrewed's idea of an external collar. I think the external collar would be easier. It's not a bad idea, however.

 

[jwmelvin]

Oh, I see. You mean a metal ring pressed into a well in the gear, coaxial with the gear rotational axis. It's similar to homebrewed's idea of an external collar. I think the external collar would be easier. It's not a bad idea, however.

Oh I see you meant a brass insert for just the set screw. I think you’d be tight on space for that.

I agree the outer collar would work well. That lets the plastic print define the bore and uses the collar for set-screw threads.

 

[lesrhorer]

We all choose our paths.

Oh, yes, to be sure. Don't get me wrong, it is a great idea. It is surely the quietest, most accurate, longest lasting solution. The gear solution will be accurate enough (at least as accurate as the original change gears), and I am hoping the plastic gear will be much quieter than the metal gear train. It certainly should be. Given the tiny amount of torque, it should hopefully last a very long time.

Should you change your mind, I'd offer to broach your timing pulleys.

That is exceptionally kind of you! If the gear solution turns out to be any trouble at all, I will definitely take you up on your offer.

I have a small metric set, 4, 5, 6 & 8mm keyway broaches. I found broaching on a lathe to be possible but difficult. I have a 3T arbor press, so broaching is much easier.

Definitely.

I am installing my own ELS system on my lathe. I wrote my own code for it using a Teensy 4.1. Going to be fun. I'm using a touch panel display rather than fixed buttons.

I thought about that, but the situation is simple enough that I think buttons will be little enough trouble.

View attachment 418969View attachment 418970
Yes, need to get the rats nest under control! I will probably design a PCB carrier board before I am done with this. Then there will be hardly any loose wires.

Ahem... did I say anything?