Planetary gears (involute) printed in 3D don't fit in the ring gear.

[chrisb]

If you are done I would like to see the result in the showcase section of the forum.

[ian.rees]

I found the gear workbench https://github.com/looooo/FCGear which has a few more parameters, but no internal gears - so I am going to try using this for the external (with more slack) and the built in gear for the ring...

The involute curve is the same for external or internal gears, so you can make the ring gear by cutting an external gear out of a bigger solid. The addendum and dedendum parameters will need to be flipped around (the addendum of the external gear becomes the dedendum of the ring gear). Also, in general, when there's a large gear ratio involved the smaller gear will sometimes need more undercut. -Ian-

Edit: had transposed internal/external...

[pperrin]

If you are done I would like to see the result in the showcase section of the forum.

Still in progress! got as far a -.2mm backlash, .7 head and -.5 clearance... to get one of the rings working! still tweeking... there won't be much to see - cos I am 3d printing I am doing individual components. But happy to share once done

[pperrin]

I found the gear workbench https://github.com/looooo/FCGear which has a few more parameters, but no internal gears - so I am going to try using this for the external (with more slack) and the built in gear for the ring...

The involute curve is the same for external or internal gears, so you can make the ring gear by cutting an external gear out of a bigger solid. The addendum and dedendum parameters will need to be flipped around (the addendum of the external gear becomes the dedendum of the ring gear). Also, in general, when there's a large gear ratio involved the smaller gear will sometimes need more undercut. -Ian-

Edit: had transposed internal/external...

What does the undercut do?

With the defaults the ring prints way too small - so I have played with backlash, head and clearance...Not very involute now - but its only a model(!).

[ian.rees]

Here's an illustration of undercut - http://lcamtuf.coredump.cx/gcnc/39-undercuts.jpg