A couple of epoxy tricks I picked up during my career as a architectural model builder.

1. Squeeze the epoxy out in two side by side ribbons. Layout the ribbons simultaniously and judge the proportions by the length of the line. Don't trust the marks on the little tubes, a small air bubble inside one of the tubes can throw things way off. Much more accurate than judging the size of two blobs. Doing both parts at the same time means that both ribbons spread out at the same rate. If you do one part first it flattens out and you can't compare it's size to the second part as accurately. By making a linear ribbon you can see small differences more easily. A 25% difference in a 1" long ribbon shows up as a .25", in a round blob it makes a difference of less than .088", since area is a function of the radius squared.

2. Squirt the ribbon into the corner of a plastic sandwich bag. close the bag and squeeze the epoxy into a corner and twist it into a little 'strawberry'. Knead the bag to mix and snip of the corner with a sharp blade for a handy applicator. If you mix on a piece of paper or alum. foil its hard to prevent it from spreading out, you don't know if the part that is spread out is epoxy A or B or a mix of the two, possibly upsetting your proportions. In the plastic bag you can be sure that every drop of both parts gets into the mix.

3. Use an epoxy filler for most applications. The filler increases the surface area of the matrix and increases the overall strength as well as improves the gap filling and flexibility. Same reason we add aggregate to concrete to make it stronger than plain cement. You can purchase commercial fillers such as ground walnut shells or glass 'micro-spheres' from the epoxy suppler or from most model building shops. Do to the increased surface area the epoxy will set faster, so use the slow stuff. Adding 50% filler to 5 min. epoxy will make is set in about 30 seconds.

4. Clean up with regular household vinegar. A little vinegar on a paper towel will wipe off any epoxy that gets in the wrong place or is squeezed out of the joints, and it won't damage cork, varnish or metal fittings.

I have used Devcon 2-Ton epoxy that sat on a shelf for 2 years or more with no appearant problems, heat will ruin it quickly however. Just make sure you store it in a cool place.