The intent of this post is to shed light on the misconception that a rotation speed of 30 RPM could quite possibly be too fast for an Epoxy Mixer. Without supporting information, such a contention could be misleading.

The key, as pointed out by Tom Kirkman, is the weight of the mixing ball , relative to the viscosity of the epoxy components, plus the secondary effect of the angle of the mixing cup, which affects the gravity pull on the mixing ball.

Factually, an experimental epoxy mixer was built which successfully operated at 60 RPM. It used a larger size mixing cup to handle the large mixing ball. The mixing ball was sufficiently heavy that it only allowed the ball to rotate appoximately 45 degrees before gravity pulled the ball back down to the bottom of the cup, in spite of the viscosity drag of the epoxy clinging to the ball. This 60 RPM mixer worked successfully, but it was too large for practical purposes.

In subsequent experiments, it was determined that for a 30 RPM Epoxy Mixer - Tilting the 2 oz. mixing cup at an angle of 35 degrees and using a mixing ball or rod, weighing at least 3/4 oz. resulted in a 30 RPM Epoxy Mixer, which performs extremely well, yielding in about 3 minutes, a thoroughly mixed epoxy that was entirely without bubbles or micro-bubbles.

That's the only problem with a faster motor like that though, you have use a larger and heavier ball or rod. At some point it starts to get out of hand. I guess you could use a 200rpm motor if you were willing to use a 1/2 pound ball!!!

I think the readily available 18rpm motors offer the best compromise overall. Any slower and the mix will start to gel and set before you can get it mixed thoroughly enough and any faster and you have to use much heavier mixing balls. With the 18rpm speed you end up with the best overall compromise and workability in terms of quick mixing time, small mixing machine, and low cost.

I'm not saying that faster motors won't do a good job if you get the right size mixing ball and cup angle, just that 18rpm seems to offer the best all around compromise of everything involved. I would guess that motors in the 15rpm to 20rpm range would be about as good if they even make them in those speeds.

I bought one of the 30 RPM mixers and the pot was just too large for me. So I used the majority of the parts and made one with a 15 RPM motor mixed up a sample batch and all worked well, found out that I needed to use a 1/2 in. ball to get it to mix well. Used it for the first time last night and everything went flawless. At the same time I bought the 15 RPM motor I also bought a 20 RPM motor just in case. But for right now the 15 seems to be fine.