Joining Surfaces

[JimCarruthers]

You can't "merge" trimmed surfaces, just join them, if that's what you're trying to do. To merge surfaces you need adjacent, untrimmed edges. Merge doesn't magically take separate surfaces and turn them into one, it will only do it if they're already properly setup for it to work.

[duderender]

ahh, so this is different than in Pro/ENGINEER... so Join... hmmm I will retry as I thought I tried join as well.

So, when is it appropriate to use merge?

[andrewjohn81]

If you want one surface out of two. That is when merge is appropriate.

Many cases you shrink the surfaces, if they were trim surfaces, make sure they are similar parameters possibly by rebuilding, then use the merge surfaces.

Unless you do some well thought preplanning you will most likely end up changing the shape slightly if you do that causing it to possibly not join to nearby geometries.

If you have two tangent planar surfaces, trims or not, you can almost always use the MergeAllSurfaces command. You can run this on Joined surfaces and it will only work on the surfaces that can be merged. I think I remember it also works on surfaces whos edges are tangent and have the same parameterization. This tool is perfect when you create half of an object, then simply mirror and join it. Run this to shrink that surface a bit more and get rid of the "seem" in the middle. Don't forget to inspect the surfaces after though. Any time you just let the computer do something for you it's always good to check it. Sometimes it just goofs up.

[duderender]

So I would suppose that unless you merge the surfaces you would see a break in the curvature analysis?

As an exercise I was modeling an industrial designer chair and I will post it so there is a visual example of what I'm doing. This is a bit of a training exercise so that I can apply my Pro/ENGINEER surface modeling skillset in Rhino but there seems to be a few things different in functionality and terminology for tools.

Thanks!

[andrewjohn81]

reguarding the curvature analysis: you are correct. You would see a break.

[JimCarruthers]

No, it's not necessary to "merge" surfaces to get a smooth curvature analysis. Joining doesn't really matter either, it'll take away the visible seam but it doesn't make things smooth that weren't before. The Herk model in my advanced Rhino training CD contains 400 surfaces, none of them "merged"--http://www.hydraulicdesign.net/advancedtraining.htm (http://www.hydraulicdesign.net/advancedtraining.htm)

[andrewjohn81]

sorry, I was thinking curvature graph

curvature analysis works fine.

curvature graph, however, will break any time the parameters are completely different, even though the objects next to eachother are completely tangent. I was thinking that was what you were saying.

And you don't always see a break, but generally you do.

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