This week's process with accompanying photos:
Design an object in Rhino that might test the limits of this fabrication method. Mine has sharp edges that might be dulled by the milling job, and angles that must meet perfectly in the mold.
Arrange the file for MasterCam: we are first milling the positive, so I simply cut the object in half, built walls around it to hold the Smooth-On and ensure that the second half is going to
be perfectly matched up with the top half. I needed male and female joints to ensure this perfect meeting, so I added them as well. I decided not to include the pour hole in the Rhino file and
just add a hole with a blade later on.
Set up the MasterCam file. This depends on a really well prepared Rhino file: where do you need surfaces, curves, or points? I went back and forth between the two to hone the toolpaths.
I had a collision at the end of the mill- the shank of the tool hit the walls of the mold in half of the mold. I completely missed this and didn't figure out how I could have missed it until I
sent Justin a screenshot of my red-free simulation (first image above) and he pointed out that the collision only shows up in red if the collision checking settings are turned on for "shank" and
"shaft" in the verification window (second image above). Big mistake. It would have been a bit-breaking mistake with any other material than wax. Lesson learned.
Mill the provided wax block (3" x 6" x 1.5") with the Intelitek 3-axis milling machine. This was a new milling machine for me and I was surprised to find how slow it was. My mill took nearly 3
hours, which is mostly my fault because I decided to go with a stepover of 1/64, which is ridiculous, but I really wanted a super smooth surface. Still, the machine seemed to stall and was generally
very sluggish. Unlike the Onsrud which takes your whole G-code and changes bit automatically, the Intelitek needs you to manually change tools, so I uploaded each g-code separately and switched
between tools as I went.
The good thing about milling separate g-codes is that you can add things that you've missed. I realized near the end of my scallop toolpath that I needed to send a flat endmill around the male parts
of the joint to make sure the other half of the mold would fit perfectly, so I went back into Rhino, exported those curves, and added them to the contour toolpath before changing bits.
Bring the positive mold into the casting room, spray it down with mold release, and begin mixing the Smooth-On OOMOO in a 1:1 ratio. Mix with horiztontal strokes to avoid churning up bubbles.
Smack the container on the table repeatedly to raise bubbles to the top. Pour from high above, in a long skinny stream, so that the bubbles are stretched out and pop as they fall. Once the mold
is filled to the top, smack it down on the table repeatedly to help get rid of bubbles.
The mold looks good, but...
Unfortunately... I made a critical error in Rhino. The two halves do not align correctly. I had to shave off the joints and put the mold together in the most slipshod way imaginable. I aligned
the halves by sight and used hot glue in a desperate attempt to make them stay put, but I knew there was no chance they would not slip. I didn't move and shake the mold around to make sure the
HydroStone was getting in to every nook and cranny because that would have exacerbated the slip even more.
I mixed 33 grams of water with 100 grams of Drystone. I left the cast overnight and came back to what I knew would not be a pretty sight. The sharp corners are nonexistant because I couldn't
shake the mold around to fill them up, and of course the halves are not at all aligned. :(
I came in this morning and cast the two halves separately, with Hydrostone this time, because I know to correct this problem I will have to go back to the beginning and fix the alignment issue
in Rhino, mill again, and cast again, which I don't have time to do, but I would like to resolve the issue. The cast worked well with the exception of the points, which almost all broke off.
However if the mold had aligned perfectly I think the points would be much stronger, in this separate cast they become too thin to hold together.