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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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1. Make sure all your stuff is ready to go. Lay it out neatly on tables so it's easy to work with. Put a layer of painter's plastic over the table so you don't destroy it with epoxy.
2. Wet the fabric with epoxy.
   1. This is where the backing comes into play. To check if the fibers are appropriately wet, check the backside and look on the wax paper. If the wax paper looks wet, you're good to go. If it's dry, add more epoxy.
   2. Once wet, blot the fabric with a paper towel to remove excess epoxy (and weight!)
3. Put the fabric into the mold. 
   1. This process will depend a lot on your part and it's geometry.
   2. Take your time, make sure things are smooth and pretty and there aren't bubbles in the fabric.
4. Bag the layup.
   1. As applicable, put the mylar (Frekote side DOWN) onto your composite. Smooth it out nicely to give your part a gorgeous surface finish. 
      1. Only put mylar where you want the layup to be smooth and it's not already touching the mold.
   2. Put peel ply over the mylar on everything that has epoxy on it.
      1. Peel ply helps you remove the breather, so it doesn't stick to your layup like a beard of cotton.
   3. Put breather over the peel ply.
      1. Don't let the breather touch epoxy. Trust me on this one.
      2. Breather is important because it helps "distribute the vacuum" over the whole layup. Without breather, the vacuum tube would only suck down in one spot of the vacuum bag, and that would be sad. Breather helps distribute that pressure evenly over the layup.
   4. Line the mold with vacuum tape, and put the vacuum bag over the mold.
      1. first, wipe off the mold with IPA where the tape is going so the tape can stick to a clean surface.
      2. Tack the corners of the bag down first, then slowly seal the rest of the edges. It's important to make sure that all the edges are sealed or the vacuum pump won't actually pull a vacuum.
      3. Do not, I repeat, do not get epoxy on the vacuum tape. It will never stick. Never. 
      4. Make sure to leave room for the vacuum hose.
   5. Seal everything up, check it, then check it again.
   6. Turn on the pump!
      1. watch with satisfaction as the vacuum bag sucks down around your beautiful composite part.
5. Let it cure. 
   1. Patience, young padawan.
6. Unbag it! 
   1. Careful not to stab yourself on sharp composite edges.
   2. Spend an appropriate amount of time admiring your layup, then sand it and finish it if needed.