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Mitch's Second Fillet Challenge

Summary: Here's another example sent in by Mitch Heynick. I'll admit, this one stumped me but Pascal figured it out. Mitch writes: Fillet all the surfaces except bottom with a constant radius of 5. –Mitch
Update: 6/6/2007: Alternate solution added (view bottom of page.) –Tan W.H

Mitch's second challenge

mitch2_01.jpg Original polysurface. Use MergeAllFaces to clean up the divided faces.

mitch2_02a.jpg mitch2_02b.jpg FilletEdge leaves a hole. There is not an obvious way to cleanly fill this, especially as a fillet. The hard part is that the horizontal fillets along the top on either side of the gap are not in line with one another. To accomodate this step back, there needs to be a surface stepping back from the angled face to the large vertical face. Undo.

mitch2_03a.jpg mitch2_03b.jpg Create a new temporary object that contains the top surface, the angled rectangular surface, and the cut surface making the inside angle where the hole is. These are marked a, b, c. An easy way to do this is to make a polyline and extrude it.

mitch2_04a.jpg mitch2_04b.jpg Fillet the edges of this object; all you need are the edges that converge on the problem corner. The important surfaces are the small segment of sphere at the corner and the edge fillet that goes back into the original shape along the top surface. Extract these surfaces. Delete the rest of this object.

mitch2_05.jpg Redo the FilletEdge. Extract and untrim all the fillets that converge on the troublesome corner including the long fillet from the temporary object. Some of these will be very long. (Note: I have trimmed them back a little in this file to clear the view.) Extract and untrim the large vertical front face (Black).

mitch2_06a.jpg Now use surface filleting (FilletSrf, extend=no) to make the required transitions. a: Angled fillet to front face. b: Angled fillet to top horizontal fillet c: Top horizontal fillet surface to small piece of sphere from the dummy fillet. d: Top horizontal fillet surface to long (red) dummy fillet.

mitch2_07a.jpg mitch2_07b.jpg These are all piled together and need to be trimmed to one another's edges. Then the untrimmed fillets, the front face retrimmed, and all joined up. Only a very small piece of the long 'dummy' fillet is actually used, along with some of the corner sphere. I found it easier to delete the bottom surfaces and then Cap the object when everything else was joined up. -PG.

– nice work John and Pascal!

Alternate solution

Download Rhino 3dm file.

mitchchallenge2-twh.jpg Alternate solution. Instructions available in the 3dm file. -Tan W.H.
rhino/foursrfangle.txt · Last modified: 2016/06/14 by jb