Creating an internal gear for servo horns

@Huub Buis The plastic servo horns are already POM I think and the internal splines just get chewed up with higher torques, the gears inside the servos are all steel and I have chewed a few gears, so at higher torques its possible to strip steel gears but thats mainly me pushing the servos past the upper torque levels. My servos have a holding torque of 70kg at 1cm and I have pushed them past that point.
 
For such tiny splines, you ought to be able to get away with a form tool straight to profile... You'll have to undercut between the retention flange and the end of the splines so there's somewhere for the chips to break cleanly... Or get innovative and have the flange as a separate piece that's added in after the splines are cut with a broach.
 
djb-systems said:
@Huub Buis The plastic servo horns are already POM I think and the internal splines just get chewed up with higher torques, the gears inside the servos are all steel and I have chewed a few gears, so at higher torques its possible to strip steel gears but thats mainly me pushing the servos past the upper torque levels. My servos have a holding torque of 70kg at 1cm and I have pushed them past that point.
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My servo's (25 kg cm) have an aluminum servo horn. I have used then 5 years (electronic clutch, motor bike) and never had a problem. Pushing beyond the limits has its risks.
If the original POM or PA6 (Nylon) servo horn doesn't last, a 3D printed part won't last at all. An aluminum servo horn could do a better job. Maybe brass so you can solder the 2 parts together.
 
@Huub Buis

Yeah, for some reason my servos didnt come with any aluminium horns only the plastic ones, and they use a non standard 18T setup instead of the usual 25T or I wouldnt have as much of an issue as metal horns are easy to get for 25T. My 70 Kg cm are slightly underpowered for the application but getting servos at 100 Kg cm+ gets very expensive when you need 18 of them.
 
Yeah and that was my first try, ordered twice never turned up, had too many bad experiences with AliExpress, Alibaba to waste more money.
 
@fixit

Thats an idea, would have to look at my design to see if I could do that and test it for any slippage. Hmmm good thought, although I still want to try and do my own internal spline but at least your suggestion would get me going.
 
You could try "molding" using this technique:
and using the gear as mould. You can solve/remove super glue using aceton (nail paint remover)
 
A rotary broach would likely do the job, and much more quickly than a shaper. The challenge for you would be making the cutter -- it would be much easier with a mill and I get the impression that you don't have one.

If the servo's splined shaft is made out of steel you might be able to sacrifice one of your servos to make a cutter. You'd have to harden it for aluminum. For that matter, maybe it could be used to make a small broach.....
 
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