Pete Roszyk gave an excellent demo on mixing epoxy at R2K1 using a digital scale. One feature that I found really desireable is being able to mix by weight with only one cup. I use either a plunger pump for batches 1.5 to 9 oz, or pour using measures for larger batches. The plunger pumps can suddenly die with no warning, so I would never start any epoxy job without a handy replacement pump. They can burp air, which can throw off your ratio, but my current resin pump has pumped over 10 gallons with few problems. I've had some die after less than a gallon.

One helpful thing using plunger pumps is to hang a 250 watt heat lamp about a foot above the plungers and turn it on about 10 minutes before use. This heats the epoxy in the plungers, so as long as you are only doing 1.5 or 3 oz batches, you always have warm epoxy, which mixes more easily and any bubbles can rise more freely, reducing the burping. Once you get to know your pump, you know when it is likely to burp and you can stop the stroke, back up an appropriate amount and continue. Knowing what is appropriate can only be acquired with a supporting scale and practice, so I wasted a lot of batches in my early years of using pumps.

For batches smaller than 1.5 oz I use a homemade balance. It has a place for the hardner on one side at 100 units distance from the pivot, and a place for resin at 43 units distance on the other side. (This is for System Three epoxy, which has a hardner to resin weight ratio of 0.43) It requires two cups and they have to be balanced using a counter weight before adding resin or hardner. This allows quite small batches as the balance is accurate down to a single drop, so it's nice to not have to waste epoxy. The disadvantage is that it requires two cups. I usually pour from the resin cup to the hardner, mix and pour back, mix, and repeat twice.

After watching Pete, I got to thinking that it's possible to make a single cup balance. My objection to the scales method is that it not only requires using a calculator for each mix but the scales cost $60 or more. (Okay, I'm just cheap, I know.) The single cup balance would have an arm on one side of the balance for setting the single cup. On the other side an arm with two pins for a weight, one pin placed at 100 units distance, the other at 143 units distance from the pivot point. (Assuming a hardner to resin ratio of 0.43) If a full size batch was wanted, say 3oz, the cup would be set near the pivot on the arm. For smaller batches, the cup would be set further out, three times as far for a 1oz batch, for example. The cup would first be balanced with a counterweight on the pin side. Then a weight with a hole in the center would be placed over the inside pin and resin poured into the the cup to balance. Then, the weight would be moved out to the outer pin and hardner added to balance.

I see one problem with this, at least for me. It is easy to overshoot when pouring resin or hardner. With the two cup method, I invariably add too much hardner, so have to do the final balance with resin. With the one cup method, there is no fall back mode. Once you over shoot the hardner, you would not know where you were on the ratio. On the other hand, the same can be said for Pete's scale method.

I guess I'll stick with my old methods but someone else might want to give the single cup balance a try.

Regards,

Al Gunther