Is there a formula or calculator for the ratio of fabric to resin?
Generally you want 50% to 50% and what Evan told me, he weighs the reinforcements and uses that figure to figure out how much resin (+ a smidge) is needed for Vacuum Infusion Process.
What some will do a burn out test on test panels to figure out the resin to reinforcements %.
Agreed, I was always taught to basically shoot for 1:1 (50%/%50%) as well.
For smaller parts, measure a resin volume at a little more than 100% of fabric weight. Final part then ends up around 50/50 resin-to-fabric. (hopefully less fabric than resin!) The extra resin gets used up on the brushes, drips, sides of mixing cup etc…
For larger parts, just mix 1 fluid oz of resin for every ounce of weight of fabric. After squeezing out the excess resin, the part should end up with a resin content in the low to mid 40% range.
The formula i use is pretty simple. For example, with 5.7oz CF, it is:
5.7oz per sq yd.
1 sq yard is 1,296 sq inches, i use 1,300 to make it easy.
So if my layers are 24"x12" pieces of fabric, that’s 288sq inches per layer.
1,300 divided by 288 comes to 4.513888…Let’s say 4.5.
I divide fabric weight, 5.7, by 4.5. Comes to 1.2666… or 1.25 to make it easy, so that’s how many fluid ounces of resin i need per layer. A 4 layer part then needs 5oz (1.25 * 4) of resin, but i would mix six to make sure i have enough.
Hope that’s not too confusing!
That would only work if one fliud once of resin weighed 1 ounce when cured, did you weigh your resin both uncured and fully cured?
Weigh the material that you cut, in grams, and round to the nearest multiple of ten. This is how much resin you should use.
Example: If the material weight is 76g, you should measure out 80g of resin.
Based on the mix ratio of your epoxy, calculate the hardener component. Example: Aeropoxy has a mix ratio of 100:27 (resin:hardener). So, given that you need to mix up 80g of resin, you need 21.6g of hardener ((80*27)/100).
This process will provide adequate epoxy to wet out the material, and enough extra to account for epoxy lost in the cup, brush, drips, etc. Most importantly, it limits your epoxy use to what is needed for the material only, thus minimizing the overall weight of the tube.
Ideally you want to be running around 70% fiber, or 30% resin/fiber… Best I’ve ever seen done with wet-layup and vacuum is about 50% so shoot for 50% (unless you have a prepreg and/or autoclave)