How to get a full remove revolve of two parts to work.

MWheeler

I am trying to make a model of a pencil with a sharpened point.  When I try and do a revolve to remove the 2 parts that make the pencil, it fails if I do a full revolve.  If I change the revolve to 359 degrees it works great, but I am left with a little sliver of the pencil.  Here is what it looks like.

_anton

It's a nonmanifoldness issue - before being subtracted from the pencil, the revolved body has an infinitely thin point at the end, which our geometry kernel disallows. Easiest fix is to extend the sketch profile in a straight line past the end of the pencil.

S1mon

When you revolve that section, you're essentially creating a part (which is then going to be removed) which is impossible in Parasolid. At the tip there is a single point where the inside of the part meets the outside. While that's possible mathematically, the kernel doesn't allow it. 

See this improvement request: 

https://forum.onshape.com/discussion/20585/better-error-handling-and-training-around-zero-thickness-parasolid-limits

There are many ways to get a conical tip on your pencil model. The most direct change would be to modify your sketch so that there's no zero thickness at the tip. 

Better practice would be to revolve a conical surface and split the parts. In general, it's a waste to create faces that aren't needed or part of the actual model. You can't always avoid this, but in this case it's easy.

_anton

It's a nonmanifoldness issue - before being subtracted from the pencil, the revolved body has an infinitely thin point at the end, which our geometry kernel disallows. Easiest fix is to extend the sketch profile in a straight line past the end of the pencil.

S1mon

When you revolve that section, you're essentially creating a part (which is then going to be removed) which is impossible in Parasolid. At the tip there is a single point where the inside of the part meets the outside. While that's possible mathematically, the kernel doesn't allow it. 

See this improvement request: 

https://forum.onshape.com/discussion/20585/better-error-handling-and-training-around-zero-thickness-parasolid-limits

There are many ways to get a conical tip on your pencil model. The most direct change would be to modify your sketch so that there's no zero thickness at the tip. 

Better practice would be to revolve a conical surface and split the parts. In general, it's a waste to create faces that aren't needed or part of the actual model. You can't always avoid this, but in this case it's easy.

MWheeler

Thanks everyone.  So it is similar to why some extrusions fail when areas meet at a point and don't share a common line or curved segment.  I run into a similar problem on a project I do with students making a stained glass window from a single sketch.  It gives me a chance to explain how the primitives need space to be able to pack in and make the 3D shape, and that Onshape is not happy when they can't get through.  Now that I know this is called a nonmanifoldness issue, I can be an even better teacher!