Wednesday, November 7, 2012

A second attempt at mold making

With the success of the last attempt at Oogoo-based mold making, I decided to try it on one of the current CNC parts.  The last attempt went well, but there were areas that could be improved.  To that end I bought real food-coloring, to get more consistent coloring of the Oogoo.  This is not important just for appearance, but also to see if it is mixed well.  I also bought a small plastic box that would contain the pattern so that I could pack the mold-material into the box around the pattern and be able to apply some reasonable force locally to get surface contact without deforming the mold elsewhere.

Here you can see the part with the steel rods that I'm using as patterns for the mounting holes.  I then put this in the container and packed Ooogoo around it as tightly as possible.  Using the plastic box really improved this step, since I could pack down the Oogoo without separating the mold from the pattern somewhere else.

I then waited about 30 minutes for the material to set and become rubbery and then pulled it out of the box, slit the mold around the edge with a box-cutter.  Here you can see the semi-separated pattern:

I then pulled out the pattern rods, slit one side of the through-hole and pulled out the pattern.

The surface quality is excellent, you can see the individual filaments of the printed part, as well as some 'flashing' where the pattern rods for the mounting holes didn't exactly meet the center hole.

You can also see where the acetic acid rusted the mounting hole peg.  Not sure how to avoid this, it seems to happen even when the pegs are oiled with vegetable oil (to act as a a release agent).

The top of the mold also shows filament marks.  Perhaps next time I'll fill the surface a bit and sand it down to improve the surface quality.  Anyway, the next step will be to cut sprues and risers to get the resin in and out of the mold.  I hope to try out actually casting parts in the next few days once I get some resin.

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