RibbonOffset help making mold for extruded paraboloid

Unrelated - but Rhino keeps getting stuck in this mode that prevents me from rotating or panning. Basically the trackpad (I’m using a MacBook Pro with M1) kicks into this mode where all I can do is zoom. Two fingers on the trackpad only zoom, similar to how it functions when holding down option with two fingers scrolling on the trackpad. I have to close the program and reopen it and it goes back to normal but it’s a really annoying bug.

Ugh. I’m sorry Pascal. The BooleanDifference command isn’t working! After wire cutting the object in half there doesn’t’ seem to be any evidence that I subtracted the paraboloid from inside it. I took a short video to show you:

I’m sure I’m doing something wrong.

The BooleanDifference is not working, because the objects (surfaces) are not intersecting. The command line will also tell you this if you check your command history (very easy to miss).

To get it working you will need to cut the box (mold) in half first and then run the command.

Thanks for writing Jari! I think that worked! However, why wouldn’t it be considered intersecting when the paraboloid object is completely enclosed within the box (mold)? I perceive that as the two objects intersecting on every surface.

Also this is really bugging me - I can’t get these objects to snap to grid lines! They just snap to the spaces between. I think at one point I had grid snap turned off but there has to be a way of getting it back to snapping to grid lines. Do you know how to fix this?

Hi Michael -

Because Rhino is a surface modeler.

That’s because the point you are moving from isn’t on a grid intersection. Snapping to the grid will only make it so that the increment is in multiples of the grid distance.
Also, using the green arrow on the Gumball will force a vertical translation.
If the object’s centroid (which is where the Gumball is placed) needs to be on a grid intersection, you’ll have to first move that with grid snapping off for the first pick point.
-wim

Hey Wim,

Thanks for the reply! That makes sense. I’m assuming you just make a point on the grid and snap to that? I got the centroid to align that way. But then the upper and lower dimensions of the box, which are what I was trying to align, are not aligned. I thought I could use align to do that but that function is acting so weird. Is this a bug or am I misinterpreting what alining to the bottom should be? You can see the z-axis in this video.

Hi Michael -

You’ll have to post the file that you are actually working with, but why would you want/need the centroid to be grid-aligned? As for the upper and lower dimensions, I take it you are not talking about dimension objects but the size of an object? It sounds like you need to scale that object but I think I’d need to see the 3dm file.
-wim

It was just an experiment to see if I could get anything to snap to the grid, but no, I don’t want to align the centroid. I just wanted to align these two boxes’ bottoms. Then I made a couple boxes to experiment with, to see if they would align to the bottom, but that didn’t work either. Aligning to the right and left worked just fine. I’m at a loss.

Paraboloid - 7.5ft x 5in.3dm (4.5 MB)

Ahhh I got it. I had to run the align command within the front view. Then it worked as it should. In perspective it got all weird.

Ugh. One more weird thing just happened. Why is this line showing up like this when I do a WireCut? It’s not centered like it was before cutting it. Probably doesn’t matter much but I can’t figure out why this is happening. Any thoughts?

@Internet_Blue Nothing to be worried about, the line you see is an isocurve. WireCut in this case leaves both sides of the cuts. Behind the scenes it is a boolean operation. The extrusion you make with the wirecut is a larger shape and this forms the basis for the resulting polysurface on the top side. If you would run _ShrinkTrimmedSrf on that top part it will have that isocurve aligned again in the center.

Thank you Gijs!! Could you help with one more thing too? I have to change the orientation slightly of the vertical wall in this paraboloid that I’m trying to make and I have to maintain the concave surface without making it shorter.

In this picture I’ve changed the angle of the wall by 3 degrees and now have a gap on the convex surface. I could obviously just move the wall in a little bit and trim the convex curve, but like I said, I can’t change that dimension.

Is there a way to continue the curve so that it meets up with the vertical wall and also maintain its parabolic form?

Hello- use Extend with Type=Natural.

-Pascal

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The Natural command definitely continues the parabolic curve? It’s not just creating a new curve or spline that resembles a parabola curve?

Here, MarkFocii works on an extended parabolic curve.

-Pascal

Oh man, somehow the perspective view got locked now :sweat:

Paraboloid - 7.5ft x 5in.3dm (3.0 MB)

Hello- the projection is parallel - you can either change that to Perspective, or use Ctrl-Shift down RMB drag to knock the view out of plan.

-Pascal