On Sun, 25 Nov 2012 21:37:22 -0800, "anorton"
wrote:

2. If you did not mind making the part smaller and had not already milled
most of the slot, you could have welded or screwed in sheets of aluminum to
raise the flat surface rather than mill the slot.

Have seen this done. Has issues and the better it is welded, the harder it is
to repair when it eventually fails.

3. Make a jig to guide a hand-held dremel or die grinder. You could either
use an end-cutting bit or an abrasive cutting wheel. It depends which corner
you want the radius to be on.

Only new idea I could think of before asking here was to make a wedged shaped
end shoe for the smaller of the two routers I have been using and use a pointed
end bit. Think they are made for plunge cuts so I'm not sure how well they
would work cutting flat.

4. Cut out the center section containing the slot. Weld in place a thinner
piece to form the slot.

Wish I had done this to begin with. Originally *was* two pieces! Had access to
TIG then... My MIG warped it way more than I expected building up a pad on the
outside so the wall thickness will remain the same.

BTW, I assume you know that the vertical edges of the slot should be angled
slightly to let the part pop out of the mold more easily.

Oh yes! Though rotational molding is probably the most forgiving of any
process. I have seen simple cubes and cylinders made in zero draft molds.
Absolutely not recommended for any complex shaped part.
--
William