Surface Additive Function? Trying to mathematically add two surfaces together

I’m not sure if I know how to convey this exactly, but I used to have a CAM software called Aspire where, if I loaded two surfaces into the same file, they would just pile on top of each other. So if I had a curved, and I then loaded that same curved surface into the program again, the surface curve would be twice as tall and twice as steep. OR, if I had the surface in the file and then I loaded a flipped (along the z axis) surface to the file, I would just end up with a flat surface, because all the curves would just cancel each other out. I ended up using this function when I was compression molding a pre-machined core. I needed to see exactly what I needed to machine on the flat core before it went under pressure. So I used my female mold surface with male features in it and combined that with its reciprocal but without the features on the mold. This left only the flat surface with the features and gave me the surface that I needed to machine.

What I’m looking for is a way to do this in Rhino. I no longer have the Aspire software, and frankly, it wasn’t that good anyway. Is there a way for me to combine the two pictured surfaces? Essentially, I want to smash them together along the z-axis and be left with a flat surface except for the parts that will be machined before my core goes under pressure.

I’ve attached an image in Rhino with the two surfaces that I want to combine, and then I’ve also attached an old screen shot that I took of the end result I’m looking for and was able to make in Aspire using the function I’m describing.

Hello - I see exactly what you are getting at and I do not see, off hand, a good way to do this - is the resulting object a surface or polysurface that you need to be an accurate thing to machine(I think yes) Or can it be a mesh representation of the desired result? - I have a feeling it might all be more tractable, in fact maybe not hard at all, using meshes - @DanielPiker — am I even in the right universe?

-Pascal

Yes, taking a grid of points, intersecting lines with the surfaces, then making a mesh which sums the heights is fairly straightforward in Grasshopper. Fully vertical parts might cause problems though, and the crease sharpness is limited by the resolution of the mesh
addmeshheights.gh (93.5 KB)

I am looking for something that I can machine, correct. We need it to be pretty accurate, and I know there are some limiting factors with this method (for instance, the rocker and concave of the surface actually would lengthen the distance between features on the flat surface, and then the machined core would wrap around the mold and bring the features slightly closer together along the X and Y axis, depending on the amount of curvature. I have some ideas for how to tackle that, just measuring point to point along the flat axis and then projecting a line from those same two points and measuring the length of the curve, taking the difference, and pushing those features away from each other that amount. It’s imperfect, but it’s close enough that it works, and there can be small fluctuations in epoxy height that fill the tiny gaps.

This is the function in Aspire. This guy extrudes a bugle shape on top of a curved dish. It’s almost like projecting a surface onto another surface.

@DanielPiker, that is exactly what I want to do, though I certainly would prefer staying out of Grasshopper if there’s any way for me to do so, since I frankly just don’t know what I’m doing there. Willing to learn if that’s the only option.

What form do you have the two surfaces in now?
If the one with the features on is a trimmed surface, maybe you could make a copy and Untrim it, then use Flow Along Surface to transfer those features to a flat surface.

I was able to get it to work with “flow along surface.” It was definitely a little tricky but SUPER cool. We are going to test this out.

Here’s the final flat surface. That center piece is a mounting area and it gets pressed into a concave that will amount to it being flat. Pretty stoked. Thank you for the help!

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