Here are some tips that I would like to share with you to hopefully make your holds better.
Making the molds are a very important step in the process. Having a bad mold means having a bad hold. Some important things to consider:
1) Shape. Make it with nice soft rounded edges & tendon friendly.2) Bolt location. Where are you going to put the bolt? Consider the shape, and place the bolt hole and countersink in an area that will provide maximum strenth and to aviod odd and irregular forces. Put it as close to the center as possible. Make sure it's not near a 'thin' part of the hold.
3) Strength. Consider the shape and how you will be using/grabbing the hold. Make sure the hold is thick enough and has enough support so that it won't fracture during use. Study commercially available holds and see how they make theirs.
4) Bolt hole allignment. Make SURE your bolt hole is perpandicular to the base. That green foam is soft and easy to drill. I use a drill press to make my holes, as I am also interrested in woodworking. It's best to use 1 bit to make the hole for the bolt AND the countersink. I make my countersink holes 3/4" and I find this is the diameter of most plastic holds as well (Pusher, etc.) You can make a drill bit to drill the foam out of a 3/4" dowel. See directions and photos linked.
4 a) WHAT IS GREEN FOAM? Go to Wal-Mart and pay a visit to their 'craft' section. Yes, they have one! It's where all the cloth material is. Look for the aisle where they have paints, etc. On the other side of this aisle, there will probably be some floral arrangement supplies. Included here is the 'green foam'. AHH! That's what it is!! Be careful, though. There are at least 2 kinds of green foam that I'm aware of. One is coarse, and you can see it has larger air pockets. Get the other kind that is smoother. I've found it cheaper at craft stores, such at Pat Catan's - a discount craft chain, for about 1/4 the price.
5) Use any tool you can think of to shape your mold. My favorites are the cureved can opener (like on a pocket knife), wooden pencils with the erasers pulled out, various knives, and my fingers. Your skin is abrasive enough to shape the foam. I also use 80 grit sandpaper to round edges and get a rough shape, then smoothe it out with a final sanding with 120 grit. A thorough but careful vacuuming at the end gets all the bits out of the nooks and crannies.
6) It's sometimes easier to drill the countersink and bolt hole before you start shaping the hold. Work around the hole to make sure it's in a spot that allows for maximum strength.
7) If you are using the silicone out of the tube, when placing it around the mold be very careful to not leave any voids. These voids will turn into bumps and razor sharp ridges on your molds, making it more labor intensive to smooth out after de-molding.
8) You don't need a full form that rests on its back for a mold. You can simply make a shell, and then invert the mold onto a peice of MDF, plywood, etc after pouring the concrete into your mold. Be careful to make your concrete 'thick' enough to allow this, and be sure to not let too much escape. Your hold could be ruined. It's also difficult to make sure that your bolt hole/countersink is perpandicular to the back.