Thanks. I am turning my Monster mill at 240 rpm with my PowerGrinder.org 1/2 hp motor which has a 7.5:1 reduction. Monster recommends a rpm of roughly 200 rpm, but I don't know if their recommendation has to do with mechanical capacity (bearing max speed) or grain crushing efficiency. If you have had good luck with grinding speeds of over 240 rpm, I won't worry about 240 rpm being too fast. Thanks again for the reply.
Besides being a homebrewer, I'm also the Service Engineering Representative for Timken (bearings) here in the pacific nw. This probably has ball bearings in it. 240 rpm is childs play for a ball bearing. A ball bearing can easily handle speeds of 2000+ rpm. 240 rpm is considered a slow speed environmnet for a ball bearing.
If you double the speed of a bearing, you cut the bearing life in half. If you double the load on a bearing you cut the life by 90%. So, increasing the speed of this machine, won't have a noticeable affect on the bearings. You'll crush just as much grain with it at high speeds as low. You'll just crush it faster at 240 rpm. If you increase the crush enough, you might start causing issues with the bearings, but I doubt it. It's crushing grain, not rolling out hot steel.
Run it as fast as you want to run it. You'll be just fine!
