Grain mill motor

I've been using a drill to power my recently purchased grain mill but have been having mixed results. The drills speed is variable by adjusting how much you pull the trigger but only down to around 400 rpm. Because of this I've been having problems with stuck sparges due to my crush being too fine or having to mill at a larger gap of 1.2 mm but then suffering in my efficiency of only around 62%.

I couldn't afford a dedicated mill motor at the moment but I managed to score a wiper motor that a guy I know was using as a spit motor. It had a transformer to convert 240V down to 12V, a bridge rectifier to convert 12V AC to 12V DC and a switch all neatly housed in a steel box. I pulled it all out and mounted it on some board and connected it to my mill with a spider coupler. The board has rubber stoppers underneath and the whole thing sits on top of a 20 litre pail.

I haven't given it a test run yet but I'm keen to see if the constant speed of around 60 RPM will now allow me to set a smaller mill gap and hopefully improve my efficiency above 70% without risking a stuck sparge.