Spur Gear Interference

Lansteys

Hi,

Has anyone else had the issue, when creating a gear train, were teeth will interfere for a few degrees at the start and end of meshing? It is clearly noticeable on internal spur gears, and more so with a higher tooth count / smaller gear.

It can be observed within the sample file for spur gears and seems to be an issue with the geometry itself.

I have had a look at the script, but that much code is a bit beyond me.
Does anyone have anything to share regarding this, whether it is a fix or just a better diagnosis of the problem?


Thanks in advance!

kevin_o_toole_1

It looks to me like this is an issue with the displayed graphics, but not the underlying geometry.

When viewing CAD models, Onshape displays a triangle mesh approximation of the actual geometry, and it appears like the internal spur gear in the example has a somewhat low-resolution mesh. This makes it appear like the gears slightly interfere, but in reality the profiles are calculated so that they don't.

Lansteys

Thanks for you answer!
I thought that this was a possibility, though it is hard to verify and givin that the tip of the gear interferes, which I assumed to be correctly represented in the model, I had discounted this as a possibility.

I did however notice that by tuning the number of teeth the interfearance can be removed. It seems less teeth work best.

I 3D printed a set of planetary gears created with the spur gear feature using 0.5mm clearance, which I achieved by offsetting the pitch circle diameter. On my printer this is a bit tight, but the teeth shape works as it should.

kevin_o_toole_1

It looks to me like this is an issue with the displayed graphics, but not the underlying geometry.

When viewing CAD models, Onshape displays a triangle mesh approximation of the actual geometry, and it appears like the internal spur gear in the example has a somewhat low-resolution mesh. This makes it appear like the gears slightly interfere, but in reality the profiles are calculated so that they don't.

Lansteys

Thanks for you answer!
I thought that this was a possibility, though it is hard to verify and givin that the tip of the gear interferes, which I assumed to be correctly represented in the model, I had discounted this as a possibility.

I did however notice that by tuning the number of teeth the interfearance can be removed. It seems less teeth work best.

I 3D printed a set of planetary gears created with the spur gear feature using 0.5mm clearance, which I achieved by offsetting the pitch circle diameter. On my printer this is a bit tight, but the teeth shape works as it should.

dbaarda

This is kinda old, but in case anyone stumbles on this I believe the problem is/was that using an external spur gear as a negative to create an internal gear means you have to swap the addendum/dedendum and root/tip gear profile settings, and invert the sign of the backlash setting. This ensures that the internal gear teeth don't protrude too far and have sufficient clearance at the root, that the root/tip chamfers are correct, and that the backlash is not the opposite of what you intended.

The current standard Spur Gear Feature doesn't make this easy, as the addendum/dedendum settings don't have the same values, so you have to manually figure out the equivalent length offsets, and then when you change the rest of the gear geometry they don't automatically re-adjust so you have to manually calculate them again. To address this and a few other concerns I have my own updated version of Spur Gear here;

Spur Gear Feature