Motorising a hand-cranked coffee grinder
Rachel has this hand-cranked coffee grinder, which works very well, but is a lot of work to crank. Holding it while cranking it has aggravated a condition called "mommy thumb", so she made a complicated bracket to help hold it. But lately, we have been leaning towards just buying a nice (burr style) coffee grinder for a few hundred dollars. But before we do that, I figured I should try motorizing this one.
I happen to have this gear head motor that runs at about 120 RPM that would be perfect for the job. It came from an ancient mechanical cash register that was given to me in the 80s. It still worked perfectly until I wanted to see if it could subtract if I turned the motor backward. Then I took it apart. Yes, I know, today one of these would be worth quite a bit, but 30 years ago nobody knew that.
I just needed to make some coupling piece to turn the grinder from the motor. My first thought was to just have an arm that sticks out and turns the crank. This would be the simplest, but perhaps a bit dangerous with that crank flailing around.
I started by drilling two concentric holes in a piece of maple...
I also drilled a hole for a pin to lock it to the motor shaft.
Checking the fit. I neglected to take into account the knob that locks the crank in place (which I wanted to keep in place), so I had to make the whole coupling piece again, this time with room for that knob.
I then wired things up temporarily with clip leads. The motor is a capacitor run motor. I'm surprised that 60-year old capacitor still works. So far so good. I then put some coffee beans in it and let it grind.
It was very satisfying watching and listening to it grind. I set the grind to as fine as I could without having the burrs grinding against each other. But it turns out, ground this fine, it was impossible to press the hot water through the grounds with an aero press. The coffee grains just sealed up! So I have to adjust the setting.
With it proven to work, I set out to finish it up. I made a sturdier bracket for the motor, which was cut from a bracket that used to hold the washing machine motor that I used for this belt grinder.
We actually also have two $30 coffee grinders, but these don't appear to last very long, which is why we have been considering a fancy one.
The grinding burr in this hand cranked one is really good, so motorising it is a good option. It's the manly way to grind coffee!
So far we have been using it for a week.