As you can see, the spur and bevel gears only spin for a brief moment then they are stuck. I really don’t know how to fix this issue since it’s the first time it happens to me. ’
Any help is appriciated, thank you.
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Binding somewhere, bearings ok? Split the box and set the gears in and try one half. Process of elimination.
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When split, all the gears run fine. But when I close the gearbox, this happens.
I tried changing bearing to bushing and the problem is still the same.
Sounds like not enough clearance for the gears you are using.
I’m using shs 18:1 gears, a gsl sr16 split gearbox and 8mm bearing.
The problem happens only when I put in the spur and bevel gears and close the gearbox. If I don’t close the gearbox shell, they spin normally.
Both bevel and spur gear if I put them in the gearbox independently and with the gearbox closed, they each spin normally, too.
I wonder if they’re too close to each other and the circumference is rubbing, like they’re not perfectly circular or something.
Do you have another set of gears to try?
Didn’t the SHS gears need a little trimming to fit? I seem to remember a little facing off in a lathe was required to get enough clearance for shimming. 
It definitely sounds like the gears are a little big for the box… won’t be talking sheep stations but enough to cause binding. Try installing one gear and nipping up the box screws… check for free spin then take it out and try the next one. If they all free spin on their own, it’ll be a gear meshing issue.
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Try with just one gear at a time… then try bevel and spur, then spur and sector.
The common misconception is that you need to have as much of the teeth in contact between gears as possible. While that would be ideal, nothing is perfect enough for that, and shimming is sometimes more about what compromise you are willing to make.
Eg. I’d rather have 0.2 clearance between gears than 0.1, as I generally shim each gear to have 0.1 of play… if both gears move towards each other in operation they will clash and wear. Rule of thumb for 95% of builds is as long as there is about 70% of the teeth in contact it will work and last a long time. Sometimes gears will bind on the gearbox, and you have to have less than complete teeth contact .
It’s all a balancing act with choosing what concession you need to make to run best.
Another thing is maybe the bushes/bearings are not straight and true to each other. This will also cause that issue.
The gears spins fine independently when I put them in the gearbox. And the problem only happens between the spur and bevel gear, the sector and spur gear runs smoothly.
I believe the problem is with the spur and bevel combinations, or there is something wrong with my bearings.
Strangely, I did test shs bevel gear with normal metal spur gear, and they run perfectly again.
So without being able to see it would that tell you there is a problem somewhere there I would think. If it’s a dodgey SHS set some are not quite to spec depending what universe they were made and what lies you believe it could be out of spec. I have seen SHS gears that went in the bin after a close inspection.
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