Mesh from surface- Density on flat surfaces

Hey all!

I need to be able to boolean meshes with cut planes to put on my printer. These are mostly not just single flat planes, but a series of flat planes creating registration keys between parts. With Rhino’s limited mesh creation options (i.e. no filleting or chamfers), I find the best way is creating polysurfaces and converting to mesh. Unfortunately, when I get the ‘rebuild density’ slider, even at maximum density, flat surfaces remain quite light, making it hard to boolean the extremely dense meshes I am working with. Is there a way to rebuild or force a higher density of polys on flat planar surfaces? My workaround has been to bend the planes slightly before converting, but this is less than ideal.

Thanks for your time!

try this value while meshing:

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That looks like what I need but when I convert mesh all I get is the slider, is that via a different command?

Click on “Detailed Controls” if this is what you see when converting to meshes"


Then you will see:



Haha! Well don’t I feel dumb for missing that. When I set the minimum edge length it still seems to keep planar surfaces simple… Weird… Not sure if that is a display setting issue or if I am doing it wrong!

Turn off “Simple planes”

My problem was it only works on a surface at a time vs the entire polysurface. Exploding and doing each surface individually, then rejoining did the trick. Thanks for your help David!

Diego gets credit for suggesting using the Maximum edge length option.

Which version of Rhino and command are you using? The Mesh command in V7 works on polysurfaces.

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Thanks Diego!!

V6 unfortunately.

Hi -

The Mesh command in Rhino 6 also works fine on polysurfaces. Please post a file…

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Weird, I mean literally the test file I have been using is 3 straight line segments, extrude curve, then mesh the surface… Only works for me when I explode and do them separately (Like extendSrf… ugh don’t get me started on that one…)

because is an extrusion object. you have to either explode and rejoin or use _ConvertExtrusion to get the normal polysurfaces.
you can also disable using extrusion when possible from Optios> General


wow! So an extrusion is a different kind of object than a polysurface? that definitely worked! Thanks Diego! You are saving me a tonne fo time. These are the game-changing details I wish my tutorial on Udemy taught me! lol …Now if only that worked with extendSrf as well!

I think @wim or @davidcockey could explain better what’s the difference between extrusion and polysurfaces. I never use them.

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In Rhino an “extrusion” object uses a method of internally storing the shape which minimizes memory used and file size. It is limited in use to shapes created using several of the Extrude commands. The alternative to an extrusion object is to use a surface or polysurface object which can represent exactly the same shape. Use ConvertExtrusion to convert an extrustion to the corresponding surface or polysurface. Modifying extrusions such as trimming or splitting will also result in conversion to surfaces/polysurfaces.

Another method to convert an extrusion to surfaces is Explode which converts an extrusion to a surface or multiple surfaces. The user can Join the multiple surfaces into a polysurface.

Whether the Extrude commands create extrusions or surfaces/polysurfaces can be set with the UseExtrusion command. It can also be set in Options.

I always use surfaces or polysurfaces, not extrusions. Extrusion objects are only a significant advantage if the file contains a very large number of objects created using the Extrude commands. The disadvantage of using extrusion objects is certain commands behave differently if the input is an extrusion object.