tangent mate or other on multiple surfaces possible ?

gunther_schwarz444

Hi, I have a saw-tooth kind of design of two rotating parts that allow rotation in only one direction (it is for a light switch on a desk lamp, see last picture). How can I make a simulation of that ? I was trying different combinations of mate connectors, mainly tangent mate, but to no avail. Based on my reading up it is not possible in Onshape. Does anyone know if it is possible ?
The top of the part is more than one surface/line, and the tangent mate allows for only one continuous surface, that is where I fail. To make matters more complicated, the parts do not use circles, but 30-segments polygon's (workaround of a Marlin bug, the 3D firmware - having problems printing small circles). So the edge of the part are actually many many small segments.

Appreciate any help. I find this a great challenge.

Thanks in advance, Gunther


link to design: https://cad.onshape.com/documents/1a80ccb9f9942cb1b12f7e26/w/802ae260c5d8ff3c222438d1/e/2bf6e1e4f50312d53782d42a

philip_thomas

@gunther_schwarz444 - the short answer is that this is very doable in Onshape.

The reason you are unable to get the tangent mate to work is (as you suspected), that adjoining edges or faces must be tangent.
I do not know why you cannot model this in Onshape (no idea what 'Marlin' is or why a plastic switch would have 'firmware').
Works great! (only requires 2 mates)

Ok, there are a couple of 'tricks'
1) There is a dummy part (roller). This is the part that is used in the tangent mate. 3D constraint solvers are very finicky in any cad system. You want as few faces and as few-potential-solutions as possible.
2) The diameter of the roller is slightly less than the inside radius of the tooth profile. This ensures that when the roller sinks into the pocket, there is a continuous (tangent) path for it to follow - as opposed to a step change in direction if it was the same size.







https://cad.onshape.com/documents/3a9e8da7c0546b730cbcd0da/w/f8d41be4937d6768a2a6b115/e/e0c6329445ad64218f9a6f5e

If the animation step increment is 'too-large', the tangent mate may flip to the other side (again, common in CAD systems) - just move it more slowly

I hope this helps.

philip_thomas

@gunther_schwarz444 - the short answer is that this is very doable in Onshape.

The reason you are unable to get the tangent mate to work is (as you suspected), that adjoining edges or faces must be tangent.
I do not know why you cannot model this in Onshape (no idea what 'Marlin' is or why a plastic switch would have 'firmware').
Works great! (only requires 2 mates)

Ok, there are a couple of 'tricks'
1) There is a dummy part (roller). This is the part that is used in the tangent mate. 3D constraint solvers are very finicky in any cad system. You want as few faces and as few-potential-solutions as possible.
2) The diameter of the roller is slightly less than the inside radius of the tooth profile. This ensures that when the roller sinks into the pocket, there is a continuous (tangent) path for it to follow - as opposed to a step change in direction if it was the same size.







https://cad.onshape.com/documents/3a9e8da7c0546b730cbcd0da/w/f8d41be4937d6768a2a6b115/e/e0c6329445ad64218f9a6f5e

If the animation step increment is 'too-large', the tangent mate may flip to the other side (again, common in CAD systems) - just move it more slowly

I hope this helps.

gunther_schwarz444

Great answer, thanks Philip! Especially for taking the time to create a working model. I recreated it an learned a lot from it (also some other details) and I think I got it. Maybe in some cases I will have to create a design and assembly variant specific for animation where I leave out tolerances and clearances. The Marlin is the firmware of my 3D printer, and it has a bug where when printing small circles it freaks out and turns into a hopeless stuttering of the steppers. Evidently some kind of timing problems. As a workaround I converted all circles to polygons, and that did the jos for the printing. Thanks again, Gunther