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Extra geometry around boolean?


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I am working on incorporating 3DCoat into my daily workflow, which involves heavily decimated .stl files being sent to a CNC machine. Our CNC is quite fussy, and it requires the base of the object to be perfectly flat, and it doesn't like tiny, or thin polygons.

I am preparing models by extending the base a little with the Bas-Relief tool, then decimating it, and then using a cube subtracted using a boolean to give me a sharp bottom edge. However I have noticed, that 3DCoat's boolean is adding extra geometry on both sides of the cut. Is there any way to have the boolean operate without this extra geometry?  

I could try to zoom in and work my way around deleting these extra edges, but that would be fiddly and time consuming. 

Here's an image, zoomed in really close on the side edge of an object to show the extra geometry I'm referring to. (It's viewed from the side, the red X-axis is visible and horizontal.) There is similar geometry on the flat underside, a similar distance inside the edge. (Hope that makes sense)

I'm going to hazard a guess this geometry is created to assist with OpenGL (or similar) rendering to improve smoothing of joins, but I'd be happy f there was some way to disable this.




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Thanks Carlosan, 

Using the pose tool to select and set the vertices to zero is smart (and a trick I will be using), but I'm still left with quite a lot of tiny polygons on and around the bottom, just inside the edge.

In Blender, I have a SubD object, with an open bottom. I can freeze it, decimate it, and fill the bottom with tri-polys.

Maybe in 3DCoat there's a better tool than boolean to achieve the same result? I tried the 'Cut Off' tool using a rectangular cutter, but I can't see a way to precisely cut it at zero on the vertical axis, and it fills the bottom with triangulated quads.

The knife tool also.. I cant see how to make it slice across everything at zero on the vertical.

I'm sure there has to be a combination of tools to achieve what I need. I just haven't found them yet.


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Yeah, I had a try at using both the Modelling and Retopo rooms, but I couldn't see any tools which would give me a perfectly flat boolean effect on the base. 

I ended up exporting a fairly high density mesh, opened it in Blender, booleaned the bottom off it, and deleted the bottom polygon because I find decimation gives a better, cleaner result that way.

I decimated this same object down to 1024 polygons in both Blender and 3DC to compare.

Here are the three objects:


(left) the high res object with the base removed with a boolean;      (middle) Decimated in Blender;       (right) decimated in 3DCoat.

For my purposes, I prefer the result from Blender's decimation as 3DCoat's has more small fans of geometry around the base. I'm sure 3DCoat's decimation is better for many other situations, just not this one.

As always, feel free to point out existing tools I may have missed. It'd be nice if the functionality I'm looking for either already exists or gets added at some point. It's not a big deal. I was hoping I could complete a project entirely in 3DCoat, but Blender is already my core tool, so exporting a finished sculpt to there in order to trim the base and export to send to our CNC guys is no great hassle.



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