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1. Buy some RenShape.
   1. RenShape is a dense, sturdy foam that is very easy to work with. Aluminum is a preferred mold material because it is harder and less porous than the foam. But, Renshape is cheaper, lighter, and easier to manufacture, especially when the mold becomes very large.
   2. 16.821 uses this type: https://www.freemansupply.com/products/machinable-media/renshape-modeling-and-styling-boards/renshape-440-styling-board
2. Create a CAD model of what you want the mold to look like.
3. Using the CAD model, route the shape into the RenShape.
   1. Talk to Tony Tao about using the Beaverworks router (behind Todd's office)
   2. If that doesn't work, the Hobby Shop also has a CNC router that you can use with some training
4. Sand the RenShape mold.
   1. It is important to be detail oriented in the next couple of steps, because it will determine the surface finish of your part.
   2. Sand the mold to remove any imperfections or router marks.
   3. Use progressively finer grit, start at 150 and work your way up to 1500. (150, 300, 500, 1500 is usually adequate). But, depending on how rough it is off the router, the mold may not need that much sanding. 
   4. Vacuum out the mold and wipe it down with a damp paper towel. When it dries, wipe it with a dry paper towel. This removes all the sanding dust from the mold.
5. Epoxy the mold.
   1. Using epoxy, put a light coat on every surface of the mold that will come in contact with the composite materials during a layup. This includes overlapping a bit on the sides of the mold! 
      1. Coating the mold with epoxy seals the pores in the foam so that the mold does not suck up the epoxy from the layup or stick to the layup after it cures. 
      2. It's easy to apply the epoxy with a paper towel, or just smear it around with a (GLOVED) hand.
      3. Note: 16.821 uses MGS epoxy, 285 cure resin for this process (12 hour cure time). Just use something more substantial than a 5-minute epoxy. 
   2. Wait a couple of minutes, then wipe off any extra epoxy with paper towels and squeegees. 
      1. You do NOT want any pools or thick spots of epoxy; this will change the shape of the mold.
      2. You DO want a paper-thin layer of epoxy on everything.
   3. Let the epoxy cure. This will make the RenShape a darker color, but that's good. Means the epoxy soaked in like it was supposed to.
   4. Once cured, wet-sand the mold (put water on it before you sand it) one more time with very fine grit sandpaper (1500 grit or so).
      1. after wet-sanding, wipe the mold down with acetone to clean it up.

You did it! That's how you make a mold.

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