# Problem making a void in a solid

This is probably not OS X specific.

I have a simple test case here. I simply want to remove a small cylinder from inside a larger cylinder to make a void. Here’s a screenshot.

You can see the smaller “coin” inside the larger cylinder - I want to remove that so there is avoid. I’ve tried Difference and Boolean Split and searched high and low. It seems that this is possible and I think I’ve even done it in the past!

Rhino is a surface modeler. That means to do the Boolean difference, the inner solid, must intersect the outer solid. If their surfaces don’t touch, there is no intersection and no Boolean. If you make a small closed cylinder that connects them; so Intersect finds clean intersection curves between the three closed polysurfaces, then a Boolean will work.

Thank you John. That’s a bummer then! What options do I have to do this? The application is this - I want to 3D print in two colors with the “outer” color being transparent and the inner color to contrast. Here is a “surface” example:

Next, I wanted to “inset” the dark grey tree/logon so a thin single layer of clear shell prints over it. Sounds like this is not possible in Rhino then.

The Level 1 Training Guide has an exercise where you make a closed, solid, polysurface that looks like a chocolate bar, and you subtract/fill voids that intersect the surface, sort of like a Hershey chocolate bar.
See if that gives you want you want.

Another option is to make three solids that have a coplanar match. Most 3D printers will print them all as a single blob.
Kyle’s excellent STL printing tutorial videos go over this:

Thanks for the video link. As for the coplanar match, I’ve actually tried that and it does not give me the clean effect I want. I’ll look at the training guide.

Ok, I found and read it - I think you are referring to the “Rhino Bar” on page 156. This is how I have been doing things for the past year or so. Now that I have the ability to print multiple colors, I wanted to take it to the next level and encapsulate a design inside a transparent shell. The effect would be very cool. I want a smoothly printed shell layer over the encapsulated design. Using three solids does indeed print the outer two as a single but the slicers treat each as a separate object with perimeters and infill so you don’t get a clean design.

But our other option gave me an idea to cheat as it were! Here’s the update and this should print pretty close to how I would like it.

The grey object is the outer container. The green is a thin cap that fits into a recess in the container. The blue object is the logo and it intersects the surface of the recess in the container. The “seam” will be hidden around the periphery where I can hide it in the print. I think this will work!

I think if you modeled these three solids; Subtracting the star from the top without deleting it, and STL printed all three of them together, you would get what you’re after.

Thanks John, basically the same idea. But hiding the “cap” seam on the surface is aesthetically better than on the side in my case. Otherwise, that’s it! I’m slicing now.

It sliced beautifully. I have to wait for another print to finish to give it a test but I like what I see in the gcode. Should work fine.

Nailed it!

This is the logo in smoke translucent PLA encapsulated in clear PLA. There is 1 layer of clear covering the logo. It looks fantastic in person and the “cap” is completely hidden in the perimeter.

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