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How to model rocks or coal with draft

Question asked by Charles Schwimmer on Jul 3, 2014
Latest reply on Jul 3, 2014 by Deepak Gupta

I'm trying to model and injection molded part to look like a pile of coal. Surprisingly to me, I found another post about this fron 2012, but it was focused on creating realistic shapes. I'm able to create shapes that are realistic enough for my needs, but problem is with adding draft to them. Here's what I've done so far: Create one basic form for a single lump of coal by creating a polygon, extruding it and then cutting facets off of the the faces normal to the direction of extrusion. Then I created a new part file, inserted a bunck of the coal parts into it, rotated each of then so that they would not look alike, then combined the solid bodies, and then did a cut extrude for a flat bottom. Before combining them, I overlapped them so that there were no voids in between them. (The idea would be to create a couple more different coal parts and insert + combine them into the part also, thereby reducing the chance of any lumps of coal looking alike). Now to be able to mold this I need to add draft. That's where I'm stuck. If you can see the picture, there are obviously huge undercuts. Drafting will change the appearance drastically, but I'll can deal with that issue. Can anyone suggest a way to add draft without tediously drafting each face? (The final pile of coal will have 60 or 70 lumps in it). Thanks!

 

Coal.PNG

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