Making a Pet Rock

This may be the first week where everything went according to plan! It was composites week, and what better to make than a pet rock? I used Hydrostone, cotton fiber, and googley eyes to produce the cutest little cotton-hydrostone-googleye creatures known to man!

Step 1: Mill the Mold

I used this week as an opportunity to do all the things I didn't get to do during the molding and casting week. I used the shop bot for 3D milling, I used hydrostone, and I used the pink foam material. The model for this assignment wasn't particularly complex -- it was an ellipsoid that I cut in half and copied to create two sides of the rock. I still managed to do it wrong; I made a positive image, but after milling I was told that I should probably do a negative image. Apparently whatever part of the composite material is pressed up against the mold will be nicer looking than the part pressed against the vacuform plastic. It ended up not mattering at all in my case *phew*. (I wanted to try both options, but the shop bot was taken over by a mass of white foam sprinkles literally all of Saturday!)

Step 2: Set up the Vacuform

I had never used hydrostone, so I was as paranoid as a dolphin in a school of tuna when I went down to set up my vacuform. It turns out it isn't scary at all! Here are some of the less obvious things I learned:

• I heard you like tubes, so I put tubes in your tubes with tubes in them. - Some tubing apparently has a bladder inside of it. This means that if you try to stick a smaller tube inside of it you have to be SURE you put it inside of the bladder, rather than just smashing the bladder. The person before me made this mistake and we couldn't figure out why until it was far too late.
• Hydrostone gets sucked dry by fabric - you may notice that the hydrostone isn't evenly distributed across the faces of my pet rocks. This is because when I poured the liquid onto the fabric, the fabric immediatley sucked all the mosture out of the hydrostone and turned it into dry mud. If I could do it again I would add a little extra water to the mix.
• Beware of crevices - I actually did cut between the two rocks because I knew the fabric would get taught across it, but I failed to remember that the same effect would happen between the stones and the edge of the cut-out area of the foam. Next time I'll try to cut out a larger area.

Don't worry, I cleaned up my mess.

Step 3: Put on Googley Eyes

It was Sunday night and my little stones came out with a great amount of personality, but something was missing... They needed googley eyes. Luckily it turns out that googley eyes are vital research tools, so a lot of people responded to my plea on the MIT ML msgs email list. Glue didn't really want to stick to the hydrostone, but after a stern talking to I managed to convince it to stay.

Bawwwwwwwwwwww look at them!

It's worth noting that these guys are REALLY strong. There are 4 layers of fabric on each one. I bet you could step on them, but who would want to?