I took a mold making workshop this past spring and wanted to see how I could combine 3d modeling and mold making techniques.
Step 1: Make a 3d model.
While modeling, of course, keep in mind the build volume and resolution of your 3d printer.
Step 2: Model the mold.
I drew a box around the object in Rhino, split both the box and object with two planes, then joined the appropriate pieces into this three part mold. Trim the mold in order to keep it as small as possible...this will save printer material. At the same time, maintain a boxy shape so you can clamp it shut. I made the mold pieces interlocking with small bumps and indentations. If you're printing with ABS or another filament with a warping tendency, these interlocks could fall out of alignment. You can always sand them down if necessary.
Step 3: Print and prep.
Print your mold...Then set up a work station outside, or in a room with proper ventilation.
You will need the following:
Large plastic cups
Poly PT Flex 70 Rubber Kit
Step 4: Apply mold release.
Spray everything a couple times, including around the mouth of the mold.
Step 5: Seal the mold.
Assemble the mold and cover all crevices with tape to help prevent leaks.
Step 6: Clamp it.
Clamp the mold as tightly as possible.
Step 7: Measure out rubber parts.
Pour equal amounts of part A and part B into separate cups. Take extra care in measuring.
Step 8: Mix thoroughly.
Mix parts together, then pour mixture into third cup and mix once more. This ensures an even distribution.
Step 9: Pour and cure.
Position your mold over the bucket to catch drips. Prop it up to make level if necessary. Let the rubber cure for at least one hour.
Step 10: Remove cast.
This may take some work. Use a screwdriver if needed.
Step 11: Done!
There is always something that could be improved upon. Personally, I think I should have spent more time orienting the grain of the print!