I'm planning on casting the J5 housing from scrap aluminum and then doing the final machining on my CNC mill. This is all hobby and I'm not that experienced at machining yet. However, I did 3D print the J5 housing to get a feel for size and possibly to and filler and turn it into a pattern for casting.

Looking at the drawing the radius of the inside corners is 2mm or would require a 4mm cutter. A bit of research on line shows that that size cutter doesn't come in a length that would reach the bottom of the J5 part. I then took the 3D print and the drawing to a friend who owns a CNC machine shop and asked him about that.

His comment was that it wasn't possible to mill to that depth and 2mm radius. The photos in the assembly manuals are a bit unclear.

So my question is: What size cutter is used for the J5 housing sold in the kit of parts? Is the radius actually larger or has some manual work been done to square off the inside corners to allow the J5 Belt Carrier full travel.