: Tom, I dont understand. If you set up the scale, with the platforms and cups
: in place, at the total mix postitions, and zero it, and then you move the
: weight side in by the proper ratio, doesnt the mass balance itself out?

: A higher mass of the arm would add to it's inertia, making it tend to
: accelerate slower and take longer to come to rest, but it shouldnt throw
: the accuracy off. Or am I missing something?

Don, you are correct for the most part. But you will have to calibrate the balance for the ratio you will be using. It is not the simple case of moving the mass or mixing cup by the ratio itself. For example, if you are using a 5:1 ratio and you place the pivit of you balance 1/6 units from one end, in theory you will be mixing the proper ratio. But in reality you won't have the proper mix ratio because the arm is longer on one side of the pivit, and it has mass to it. This can easily be corrected by placing known masses corresponding to the ratio (water comes to mind...measured proportionatly by volume to equal the mass mixing ratio). Then adjust for the actual balance point. In use, this balance requires two cups, one for hardner and one for resin.

This other way you will have just one platform and just one cup. On the other end you will have two sliding masses corresponding to each part of the correct mix ratio (If the ratio is whole numbers, then select any same objects, such as large washers, for the ratio. If the ratio is not whole numbers, then you will have to use a scale and play around with some masses to get the proper proportions). Both of these masses will be placed (hung?) at the SAME position. The position only depends on how much epoxy you wish to mix. Use a 3rd mass (can be anything)placed appropriately for zeroing your balance to the empty mixing cup.

A 4th mass can be used as Paul suggested as a (getting close) indicator and this mass will then be removed for the final few drops to be added.

Heres how it works: Place a mixing cup on the platform. Slide or hang the zeroing weight on the opposite arm of the balance to zero out the cup. Pour any amount of resin into the cup which you wish to use. Place the "resin" mass on the opposite arm in the proper position to bring back into balance. Then hang the "hardner mass" at the SAME point. (here is where you can apply the "getting close mass" on your mixing cup platform so you don't overshoot your pour). Then add hardner. Once the balance starts to move, remove the "getting close mass" and carfully add the last bit of hardner.

It was mentioned that you may want to add the hardner 1st, which certainly has its merrits, but by adding the resin 1st, you get a good picture for the amount of epoxy you want to mix, exspecially if the epoxy ratio is a larger one. If you add the hardner 1st, it may be more difficult to get an idea of how much epoxy you will be mixing.

Once you know the position of the masses vs amount of epoxy, mark the weight arm indicating the position for various size batches. Now it becomes more feasable to pour the hardner 1st with the hardner mass placed 1st at that location. If you over shoot a little, just slide the mass to balance it, add the resin mass to it, and place the getting close mass next to your cup.......

Hope this clears up the confusion. I think that the confusion lays in that several techniques have been addressed at the same time.

Tom