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I recently had 2 Kyosho OT-85 center gears (idlers) printed by Shapeways.
The gears were printed MJF PA12. Vapor smoothing or any smoothing was not an option.
The gear faces are not particularly well finished. Probably nature of the beast.
I really just wanted try and design a proper gear in 360 to see if it printed the way I wanted.
The gear is fairly nice but I just don't know if I trust it's strength.

Questions are
Are these viable gears for my TOMSE? Can they handle the stress or will they shear teeth easily?
Can annealing help in any way?
Are there much better printing solutions?

I have tried to look into machined derlin gears but $800 - $1,200 is way too steep for me.

Chuck

I guess it really depends on how much load you put them under , if you use a 10.5 brush less motor on lipo batteries then no they won't last long but if your running a 21t brushed motor on 7.2 NiMH then you'll get a reasonable life out of them . I have some Yokomo 834b gears printed by Shapeways in pa12 SLS and I test drove the car for 20+ batteries (brushed motor and NiMH battery) and inspected them for wear and other than them smoothing out some of the rough texture they were fine . Do I think they are as strong as stock gears , no they are not but they are replaceable and not too expensive .
The other option is to get them printed in Stainless steel , not as expensive as you might imagine and way cheaper than custom CNC cut gears .
Just a note about designing in Fusion 360 , it will produce a perfect gear ! A lot of the time I've found (and I've done this a lot!) that nylon injection moulded gears are slightly under size , this is because the mould is probably cut as a perfect pitch gear and the nylon shrinks as it cools in the mould so it comes out unders size , this is then incorporated into the design of the gearbox so the under size gears still mesh perfectly . In short you have to actually measure the diameter of a genuine gear then scale your modelled gear in Fusion down to match , last one I did just yesterday for a Mardave Meteor was scaled to 0.966 to match diameter , doesn't seem much but if you don't do it the mesh will be tight and the gears will overheat and die prematurely . Oh set the pressure angle to 20 as well .

One thing to precise about stainless steel printed gears : due to the nature of the process, it's a bit random in the way it works, I noticed that dimensionnal accuracy depends of the geometry and some gears may need to be undesized while other may just be fine as per their initial specifications...

It might be easier to by a replacement gear made in delrin for the Mid
https://rwracing.co.uk/shop/ols/products/optima-mid-4-acetal-idler-gear

terry.sc wrote: ↑Fri May 03, 2024 10:47 am It might be easier to by a replacement gear made in delrin for the Mid
https://rwracing.co.uk/shop/ols/products/optima-mid-4-acetal-idler-gear

Thank you so much!!!!!!
I can't believe I had not found this site!
In my eyes you may now rival the legendary GoogleFu Master Phin.
I have searched for such a gear for way longer than I care to admit.

Chuck

WHAT? 9 quid??

Do they think we're made of money??


I'm kidding, of course. Not a bad price for a low-volume custom machined part.

I'm very happy, Chuck, that you've found what exactly what you've been looking for.

Thanks Doug

It appears that to find any Google reference to the gear and find their site you must add "acetal" in the search terms.

And RWR doesn't use Kyosho's part #?

Anyways to beat that, shipping was 6 quid!

Chuck