Did you determine the critical speed rpm of your drum and set an appropriate milling rpm based on that? If not, you could be wasting your time. I know you don't have the HF mill, but for example (and as in the link I posted earlier), the critical speed of a HF drum is 133 rpm. That's when centrifugal force keeps the balls stuck to the edge of the inner surface of the drum, and no milling will happen. 50% to 70% of critical speed is pretty much where to be. So, at 60 rpm (factory set) the HF mill is only running about 45% of critical speed. It should be running about 80 to 90 rpm to be optimal. That is why so many people run their mills for a long time to get a fine grind when it should only take a couple of hours. I'm guilty of that as well. Several years ago I wrapped duct tape on the spinning shaft in the right places and my mill speed ran about 73 rpm which is 55% of critical speed. The tape worked but it's tedious to apply and measure, and it loses shape over time. I think I can do better with plastic tubing as per the link I posted.