How to remove a portion of surface thickness in 3D curve

Rhino Rhino for Windows
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1

Basically I have a cross slice of an ‘easter egg’ (curvature on all axis) and I am trying to shave a portion of it (where a gasket would fit in to lie flush with the surface, which is the reason I need to lessen the wall thickness evenly). If I try copy & scaling it and then doing a boolean difference to remove it different thicknesses are removed (actually cuts through the surface at one point). So basically from an end view I am trying to remove part of the wall thickness on a part of it, and then have that follow the curve. I thought I could create a cutting surface and then extrude it along the curve using ExtrudeSrfAlongCrv but for the curve it does not accept the 3D surface I want to cut. Any ideas on how to do this?Egg1.3dm (230.0 KB)

2

please post your .3dm rile or a sketch of what your re trying to do…
maybe a screenshot with some additional photoshop / sketch annotations ?

3

I added the file ‘Egg1’. Also I projected a box onto the curve, but what I really want is a ‘box’ that follows the parabola all the way around, which can then be extruded slightly, to then do a boolean difference with that would then cut the shell thickness roughly in half. Definitely a newbie, so bear with please :frowning:

4

Hi Gary - try:

  • ExtractSrf, Copy=Yes the outer surface.
  • OffSetSrf >Solid=No the surface twice, so that the two offsets are the gasket thickness apart.
  • UntrimBorder the two offsets, then
  • BooleanSplit your solid with the two surfaces.

Is that it?
Egg1_PG.3dm (302.1 KB)
Ah, I see that it is not - the inner is not an offset of the outer - we’ll need TweenSurfaces instead - hang on a bit.
-Pascal

5

I see where you are going, the ExtractSrf & OffsetSrf have to be part of it, not understanding the UntrimBorder… Playing with it, thanks so much Pascal

6

Hi Gary - UntrimBorder will make the offsets larger than the trimmed faces on your egg so they will stick out past the edge surfaces of the egg allowing the Boolean to work. The problem, maybe, is that the inner and outer are not offsets of each other, so the result after removing the gasket thickness will be of varying thickness - so you’ll have to decide what to do there. Another possibility is it TweenSurfaces to get the ‘mid plane’ then offset this to each side half of gasket thickness, and UntrimBorder etc.

-Pascal

7

Got it, I think I can take it from here. Thanks again, this had me stumped all morning!