Thanks for all the information!
I just spoke to West System to find out what they recommend and do in their shop. They recommend maximum vacuum up to 24 inches to make sure all the air is out and control the resin by the size and amount of holes in the bleeder cloth. The technical person went on to tell me of the $40 dollar clip board exercise they do in the boat building school that demonstrated the effectiveness of the types of bleeder cloth.
So what I’ve learned so far seems to be a formula that takes into account the size/type of lay-up, ambient conditions, mix of epoxy, amount of vacuum, and the size of the bleeder holes.
Good info! I guess I need to keep reminding myself that even 24 inches of mercury of vacuum results is still over 1,500lbs of pressure on a 1 square foot surface.
Average sea level pressure is 29.6 inches of mercury...which is the most vacuum you could achieve. I don't know how much that varies with weather systems (probably not much).
I also want to experiment with a set formula by weight of the amount of resin vs. the weight of fibers so I could possibly do away with the bleeder ply (for the most part). At least for small parts, I think you can still extract the vapors from the laminate with vacuum contact around the edge perimeter.
Last thought, when bonding to foam, I first squeegie in a thickened layer of epoxy and filler (microballoons) to fill in all the little pockets of the foam. I then lay the glass and resin on that. You get a much better bond that way and the thickened resin doesn't pull through with the vacuum (much).
