Intersect plane with mesh?

aaron_everman

Hi Everyone,

I imported a 3d scan stl file of a power tool battery pack. Is it possible to create some section curves from the mesh by intersecting it with a plane at different heights? I was thinking this would help me model some of the geometry I need for a 3d printing project.

eric_pesty

You can split the mesh along a plane though, this will give you a face you can sketch on and allows you to use the edges (I think…)

jelte_steur814

it would be cleaner just to make those planes, open the sketches, make a section cut and trace it yourself with lines/arcs. that'll make a lot cleaner geometry.
else try the 'intersect' command in the sketch. (not sure it works with meshes)

MDesign

It doesn't.

eric_pesty

You can split the mesh along a plane though, this will give you a face you can sketch on and allows you to use the edges (I think…)

MDesign

That does indeed work. good thinking.

https://forum.onshape.com/discussion/comment/112603#Comment_112603

aaron_everman

Yeah, I was able to split the mesh with a plane and then project the new mesh edges onto a sketch. Kind of a round about process but it does work. It seems weird that one can split a mesh but not intersect a mesh with a plane.

GregBrown

Yes, you can split the Mesh part (whether it is watertight or not) using a Plane. It maybe necessary to Enclose the the split part and plane(s)… Once you have a solid part you can, as @eric_pesty mentions, sketch on it and Use the edges.

Quick example: This mesh has been split into various sections. Note it is useful to have Highlight boundary edges turned ON. Better still, make a custom keyboard shortcut (mine is shift-6) to toggle in on and off :)

Now Enclose using this part and the two planes…

Sketch on that front (now analytical) surface…

… extrude it, whatever.

Or maybe shell the whole part…

aaron_everman

Cool

kenn_sebesta167

https://forum.onshape.com/discussion/comment/112633#Comment_112633

How were you able to do this? I'm trying something similar and while I can get to the point of having the mesh edge after the split, I cannot project it.

EvanReese

I'm not certain, but I don't think there was any sketch projection of the edges. Greg just used the Enclose feature with the mesh and the planes.

EvanReese

Relevant to this conversation though. I've recently been playing with curves and meshes together for workflows like this, and found that Project Curve and Intersection Curve are both coded to prevent selecting meshes, but that the functions inside them can actually handle them! I assume that the Onshape devs will cringe at all of the unconsidered issues this might cause, but I did create a version of each of them here that you can use. I strongly recommend using the "Approximate" functionality to clean them up. Otherwise the curves it makes are still seen as mesh geometry and things like Loft will be mad about it.

S1mon

@EvanReese That's a pretty amazing find. Seems like something that should be addressed by Onshape. I'm guessing that they are working on it. It sure would help to improve the abilities to do reverse engineering work.

EvanReese

Yeah, I mean sometimes being able to just slap a feature out ignore the consequences is freeing. There's probably a ton of work to do for a "real" solution, but I'm sure it's on their radar. This will certainly be handy in the interim though!

MDesign

Well then. I suspected there might be capability for doing that Evan. Thank you for for sharing I will be checking that out for sure.

kenn_sebesta167

Interestingly, if I sliced the mesh from a slightly different angle by changing the 3-point reference plane, I was able to do projections to the sketch.

And then, without me changing anything in the past, those projections lost their reference. Fortunately by then, they were already made so I just gave them a fixed constraint and didn't look back.

But there's definitely something to this workflow. Just need to figure out why, for the sketch projection, YMMV from minute to minute.