Thread: Surface Creation Help

1. Surface Creation Help

I've been doing quite a bit of 3d work, and with pretty good success. The parts have been machining out beautifully. It's been a fun process to go from idea to physical part. I am using BobCAD V20.

I occasionally run into a couple of issues, and I'm not sure how to resolve them. Probably just my own ignorance, but I can't figure it out.

If I want to create a simple surface using 3 lines (arcs) in a single plane (z=0), I select "3 Edge", choose the line segments and never get what I want! The surface generated is not in the z=0 plane, and it doesn't intersect the lines I chose as boundaries. This works pretty nicely when the lines are NOT in the same plane, but fails when the lines ARE in the same plane.

My second problem is trying to create something equivalent to 1/2 a curved cone (think longhorn). Two edges that terminate at a single point, and then a series of arcs that bridge the two edges. I can't find a surface creation method that works for this kind of geometry and I can't find a way to change the geometry to make it work for something like a "skin" or "4 edge".

I have included a file that illustrates these geometries (rename .txt to .cad). The "bottom" is the simple case with 3 arcs in the same plane. The "top" is the cone-like example with two edges and a series of arcs. The other surfaces are no problem. See the layer called "new surfaces".

Thanks for any ideas or help on this one.

Steve

2. The answer to the first is simple. You are using the wrong thing.

Instead of creating a 3 edge you need to create a Planer surface.

3 edge is for a a part with x,y,z depth while the planer surface is a flat plane of any shaped contour.

I will look at your file for the other.

Update. It appears the trouble comes from the razor edge you are trying to create using extrudes/skins/surfaces. This is not going to work.

Try placing a flat on the knife end (make it thicker not shorter if you wish to keep the length) and then later you can use booleans to make the knife edge if you like.

3. I couldn't open your file

4. I will give the "planar surface" another try. It seemed like the most logical candidate, but something didn't work right. I'm sure I worked down the entire list, but didn't have luck with any of them. I'll also consult the training videos when I get a chance.

I figured I could make my "longhorn" into a 4 sided shape with arcs overhead. I'm sure that would skin over nicely. I was just hoping there was a more direct way. It's not essential that it terminate in a sharp point, but I could recreate that afterwards with booleans. Sometimes the booleans fail for no apparent reason, but I can generally find workarounds there too. For instance a "diff" may not work, but an inverse "intersection" might. Very odd.

I can't check my file from this computer, but it's possible there was some problem in the upload. Although it has a .txt extension, it's really a V20 .cad file.

Thanks,

Steve