Motorizing the apple grinder

Although I used wooden gears for my box joint jig and my router lift before, I had only used them for making adjustments, so I was keen to try wooden gears for actual power transmission. I figured my new apple grinder would be a cool project to try this on.

The smoothness and ultimate speed that gears can handle is primarily limited by how precisely they are made. My gear program and an ink jet printer take care of precise calculation and marking, and I was hoping I'd be able to cut them out precisely enough on the bandsaw.

I used an old box fan motor. Box fan motors are typically 6-pole motors, running at only 1150 RPM on 60 Hz AC. They are also relatively powerful for fan motors, although not particularly efficient. Box fans, on full speed, consume about 200 watts.

The pinion attached to the motor shaft is cut with the wood grain parallel to the motor shaft. That way, all the teeth have about the same grain exposure. I made the pinion extra wide to make the teeth less prone to breaking.

I wedged the pinion on the motor shaft by driving a small nail between the flat spot on the motor shaft and the hole. I also shimmed the hole with paper to make the fit tighter.

I added a disk behind the pinion, with some "fan blades" on it to blow air away from the motor. Hopefully, this will draw some air through the motor for cooling.

I oiled up the gears and the dowel that I used as a shaft. If I'm using wooden gears, I might as well use a wooden shaft and bearings.

The gears didn't run super smooth, but they didn't run that badly either. It was very satisfying to watch them run! High speed wooden gears! 0K, not really that high speed, but still pretty fast.

I wanted to see how the gears would last under load. So I attached a 10-pound weight to a block of maple and hung it off the end of the shaft. I let it run for about half an hour like that.

No sign of wear, and no smoke either! So far so good!

So I figured this motor and gear arrangement should work for my apple grinder.

Here's the mount for attaching the motor to the apple grinder. I cut some holes into the mount to allow more airflow through the motor.

Before I put screws into the drum, I could safely stall the motor just by grabbing the drum with my hands. I figured with the screws in the drum, it wouldn't be able to maim a hand too badly - A useful safety feature.

I also drilled some holes in the bearing blocks to make oiling easier. Here I'm pouring some vegetable oil into the bearing. The wood absorbs oil, so it takes repeated oilings to get the bearings fully oiled.

Once the rest of the apple grinder was done, I was able to do some testing. I could grind one apple at a time, but grinding two apples at a time, it was easy to stall the motor. With three apples in the grinder, it stalled almost constantly.

The gears worked fine, but they were made to go with that motor. With that motor proving inadequate for the job, the gears weren't much use.

Next I tried a motor from a bread maker. I reused the whole motor and belt assembly. That pulley transmission used to power the paddle in the bottom of the dough pan. This motor consumes less power than the fan motor, but has more torque. It's a split-phase (capacitor run) motor, more efficient than the shaded pole style box fan motor.

I was able to grind three apples at a time with this arrangement, but the motor was very strained. Pushing the apples down hard with the plunger could still stall it.

So this motor was almost powerful enough, but not quite.

So next I decided to use a real motor. This is a one third horsepower pump motor that came from a utility pump I picked out of a dumpster.

Like most pump motors, this one doesn't have mounting flanges. So I mounted it to a piece of plywood with hose clamps, very similar to what I did with the motor for my bandsaw

To get the right speed, I needed a large pulley to go on the shaft. I made a wooden pulley, of course.

I cut a round disk on the bandsaw, then cut a groove around the circumference by making a series of cuts with the table saw. This sort of operation can be risky if not done carefully. I used a piece of scrap wood on the back to guide the wheel, and a feather board to help press it against the fence and prevent kickback. Then it was just a matter of slowly rotating the wheel into the blade (clockwise in this image)

After cutting out a square groove, I tilted the blade by about 20 degrees to bevel the edges of the slot to match the V-belt.

If you make a pulley this way, be sure to cut out a square groove before cutting the angled sides. If you start with the angle cuts, the blade will jam and kick back.

Actually, I don't know this for sure, I haven't tried cutting the bevel first, I'm not that keen to find out either.

A safer method, but requiring more setup, is to make it on a router table

Next I added some flanges to the pulley to get more support on the shaft.

I put a short piece of dowel into the flange holes to check that the shaft would mount square to the pulley.

Then weighing the flange down to glue it. I started by just weighing it down because clamping will often displace a glue joint sideways.

After letting it dry for five minutes, I figured the glue was set enough that it wouldn't slide anymore. So I clamed it with my long reach clamps If you don't have clamps like this, you could always drill some holes in the wheels to clamp through, like I did when I made these bandsaw wheels

Motor mounted on the grinder.

The motor is only held on with a C-clamp. There's no point in bolting the motor on. An apple grinder is only set up temporarily for a day or two, then it's disassembled for cleaning, and stored for the rest of the year.

Testing it with this motor. I had plenty of power to spare!

So the way to power an apple grinder is with a regular induction motor. It doesn't have to be a powerful one, Considering the bread maker motor was almost powerful enough. Any furnace motor, washer or dryer motor should be ok.

Very satisfying seeing the ground up apple pulp just dripp out of the grinder!

But the apple grinder is actually for my sister to use with her kids. Running motors and exposed pulleys with five year old kids helping might not be the best idea.

With the previous apple grinder that I built, we tend to grind anywhere from 200 to 500 kg (400 to 1000 pounds) of apples each fall, so a motor is really important. But my sister isn't planning on grinding that many apples.

So I made a hand-crank for the grinder. I ground a few apples using the crank, and it worked surprisingly fast.

The crank handle is a piece of dowel on a bolt. The bolt is recessed a little in the handle, so one doesn't get caught on the bolt that turns inside the handle.

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