Pedal-Power Apple Grinder

[Note October 2009: the pedal mill has been substantially updated since 2007, including tandem bike power.  See posts from Sept-Oct 2009 for details on the upgrades, eg. https://fiveislandsorchard.wordpress.com/2009/10/09/new-pedal-powered-apple-grinder-built/ ]

In the interest of improved aesthetics and increased Hard Times compatibility, Holly, Keith, and I have been working on a pedal-powered grinder for this year’s cidering.  After a big push last weekend, victory appears to be within our grasp.

We take as our benchmarks the antique cast iron press that we used in cider year 1, and the Insinkerator garbage dispose-all that we used last year.  The antique press could scarcely be beat from an aesthetics standpoint, but it’s yield was a meager 50%, and its capacity was relatively low.  The Insinkerator does a masterful job of liquefying apples, but its aesthetics leave much to be desired.  This is primarily because in order to keep the motor from overheating in continuous duty, we have to blast the stator windings with compressed air, and the sound of the compressor dominates the otherwise relaxing mood.  Also, between the compressor and the insinkerator itself the operation consumes close to two horsepower, and this taints the overall aesthetic of hard work and self reliance that makes cidering so pleasant.

Last year Holly and I upgraded our pressing capabilities significantly with the tie-bar press (see the design at http://www.positron.org in the 2006 cider section), and this year we improved the press further by widening the grates and adding a slick cast aluminum hand-wheel.  We had plans to build a pedal-powered grinder last year, but the press was all we could manage under the circumstances, and we settled on the Insinkerator as a fall-back position.  We did buy some key components, including 3/4″ stainless steel hex stock, 5/8″ flange-mount bearings, and a sweet 2′ diameter cast iron pulley/flywheel.  We cut a couple of shafts from the 3/4″ hex stock and turned the ends down to 5/8″, and I made a hail-Mary attempt involving a cylindrical maple drum with 8 rows of stainless steel wood screws in a helical pattern as cutters, but the screws tended to load up immediately, leading to unacceptable performance.

Undaunted, we took up the challenge once again this year.  We got some 304 stainless steel strap stock 1″ wide and 1/8″ thick, and we cut, ground, filed, and honed it to form four cutters, each about 5.5″ long and sharpened to a 75 degree angle at one edge.  I drilled and countersunk holes for wood screws, and remachined the drum on the tablesaw to accept the cutters.  I also upgraded the plywood housing that the drum runs in, including the addition of an adjustable-clearance anvil plate with a sheet of stainless steel to protect it, and gave the whole thing a couple coats of water-based polyurethane.

Since we were aiming to drive the grinder from a bicycle crank, we figured we needed a substantial gear-up relative to the pedaling rate.  Part of this was accomplished by a 3:1 chain drive stage between the main shaft of the grinder and a jackshaft that we added.  We could have hacked something up with bike chain and sprockets, but Holly scored some nice surplus 40 pitch sprockets and roller chain, so we used those (similar stuff could be bought at McMaster-Carr, which is a magnificent industrial supply company and truly an engineer’s best friend).  At Keith’s recommendation I didn’t buy a chain tool, but rather simply drifted a pin out using a hammer and nail set over a suitable gap in the bench vice, then tapped it back into place to form the desired size of loop.

Adapting from the front chainring of my old Miyata touring bike to the jackshaft was a bit trickier.  Holly and Keith are both fixed-gear zealots and called me a wuss for insisting on a freewheel in the system between the pedaler and the flywheel, but given the speeds attained by the high-speed shaft in operation I’m glad I stuck to my conservative plan.  We bought a machinable 5/8″ shaft collar from McMaster, and  turned it down to match the ID of an externally threaded bottom bracket cup provided by Keith.  With the combined mojo of a Mapp-gas plumber’s torch and Holly’s small oxyacetylene rig, we managed to braze the threaded cup onto the machined shaft collar.  I bought a 7-speed threaded freewheel for $20 at the local bike shop (Omer and Bob’s, Hanover NH, thumbs up) and they were kind enough to let me have three used chains in good condition for free.

Remarkably, the threads on the cup were still viable despite having been heated to orange-hot, and I threaded the freewheel on.  There was some runout due to imperfect alignment in the brazing process, but nothing that affected performance significantly.  I clamped the shaft collar/freewheel assembly onto the jackshaft after the 3:1 heavy chain stage was in place.

It remained to build a framework to hold the grinder and bicycle in position relative to one another so they could be connected by a loop of chain.  I accomplished this with some large scraps of maple plywood, with a chunk of 4×4 fir oriented vertically and drilled for a long 5/16″  machine bolt to secure the front fork of the bike.  I then removed the bike’s regular chain from the smallest front chainring, and spliced the used bike chain to form a new loop of suitable length to connect the largest chainring of the bike to the freewheel.  The chain runs forward and slightly up, and the hopper is within comfortable reach of the cyclist for feeding, in case the need arises for solo operation.  Using the smallest cog on the freewheel, the overall gear ratio is about 11:1, giving approximately 1000 RPM at the grinder for a brisk pedaling rate.

The whole system works surprisingly well.  The rear wheel of the bike is free and rests on the ground, and by swinging the rear end right or left the chain tension can be adjusted to some extent.  The chain loop was perhaps a link too long, so I compensated by shifting up a couple of gears; the grinding drum still spins plenty fast.  The effort to keep the system spinning in the absence of fruit is trivial compared to pedaling with no load at all.  The effort to grind an apple is noticeable but not strenuous.  The primary limitations are:

  • The support structure isn’t that stiff, resulting in some disconcerting deflections and vibrations.  I am going to add some more pieces to strengthen it further.
  • When I threw in a couple apples, they got into the mode of spinning rapidly in the opposite direction as the drum and bouncing rather than cutting.  If I prevented the apple from spinning with a stick, it was quickly ground to pulp, and I expect that this will not be a problem  once we fill the hopper with apples.
  • The apple pulp gets flung all over the place under the grinder.  I am going to make a skirt of sorts to keep it in place, similar to those I have seen on industrial equipment.
  • The pulp may be a bit coarse compared to the garbage disposal output.  It may still press out fine, and if the yield is low we can reduce the bite of the cutters by forming four rectangles of stainless sheet stock to the curvature of the drum between the cutters and screwing them in place.

The neighbors have an unkept apple tree that is drooping with fruit, and they told me they were fine with me harvesting some, so I’m going to make the changes described above and give it a whirl this weekend.

Here are a couple photos of the nearly-finished pedal-powered apple grinder.

End view, showing grinder box, drum, flywheel, sprockets, freewheel, and chain drive from bicycle:

pedal-mill-end-view.jpg

Side view from bicycler’s end, showing attachment of front fork to cider mill assembly:

pedal-mill-bike-side.jpg

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8 Responses to “Pedal-Power Apple Grinder”

  1. Jason Says:

    Gidday, after a fun community market apple pressing down here in the far south of New Zealand, I am looking for ideas for more efficient apple grinding, your bicycle powered grinder is definitely a long term goal, in the mean time I’ll try an insinkerator as seen you using on http://www.positron.org (Ben?). A question as it was not clear in the pictures, did you just attatch an extention to the insinkerator side outlet to get the pulp to drop to the bucket? is any other modification necessary, as I wondering how the pulp will move around these corners without running water through with it as you normally do with standard insinkerator usage. THANKS inspiring site

    • fiveislandsorchard Says:

      Jason:

      No water is needed – the stuff comes out on its own, sort of extrudes out in tubular form which devolves into a puddle of mush when it hits the bucket.

      You do need some means of cooling though. Our favorite method is compressed air, ported into the chamber between the housing and the windings themselves. At least on the brand we used, when you take off the wiring access panel you’re staring right at the windings, which are the part that generate the heat. So if you blow compressed air in there you can very effectively cool the windings, allowing continuous use.

      Good luck!

  2. Jason Says:

    Thats great thanks, now I’m on a mission before our next harvest market in a week!

  3. Lane Mason Says:

    Please send me more pictures of this. I would like to build something similar only to drive a wheat grinder.
    Thanks,
    Lane

  4. Molly Says:

    Hi! I’m working on a school project, and your design could be extremely helpful for us to use as a reference. Do you have any design documents, plans, and or pictures you could send me?

    Thanks!

  5. Chuck Kottke Says:

    Thanks, you’ve inspired me to try this, as I was thinking along these lines of bike-powered apple grinders, given the strenuous workout and jarring stops one gets with a hand-cranked mill! One thing I was considering, since the pulped fruit is too ‘chunky’ to press out well, was making a a pair of adjustable fluted rollers which mesh like gears to finish the mushing operation, something I noticed in a few antique mills(solid laminated maple should be tough enough, theirs was of cast iron in the 1800’s, but I haven’t a foundry for something that exotic!). Yields then should increase on par with the insinkerator pulp, and made with renewable, human-powered energy! :–)) Thanks again for the great idea, worked through with suggestions!

  6. fiveislandsorchard Says:

    Hi Chuck:

    A couple of people have asked for more details on the crushing rollers, so I’ll see if I can dig up those old design files and post what we did. We were fortunate to have access to a bridgeport mill with a manual rotary table, so we could machine them fairly precisely out of UHMW polyethylene. But a talented woodworker with decent tools or a lot of patience could probably make something workable. My only concern about wood is that we set them to run fairly tight (basically as close to zero clearance as we can tap them without getting a horrible clattering noise), and if you were doing wood rollers they would surely swell, and quite possibly jam.

    I can think of two directions to go in. One (which I think is actually pretty promising) is to basically just refine the primary shaving cylinder, so that it has more and finer cutting blades, so as to get a finer pulp off the grinder, but still with a shaving rather than a crushing action (which I have to think is more energy efficient for pedal input). Especially if you let the pulp sit for an hour or two and get juicier (which would be fine if you had enough tubs).

    If you wanted to make wooden post-crushers, you could try to figure out how to make one of them spring-loaded against the other, so that the assembly would accommodate swelling. Doesn’t seem that difficult, except at least with tooth profile we use, you can’t just drive one; there has to be a timing chain to keep them in synch, and the way we do it, changing the distance between drums would result in the drums getting out of phase.

    So anyway, if you can get access to a machine shop, I’d suggest polyethylene drums, and will scare up a drawing.

  7. liamcallaghan Says:

    I dont suppose you have drawn up any plans for this have you?
    We are just at the drawing stage and looking to build in the new year after making a batch by hand earlier this year (260 litres). Be nice to have the scratter done before the next one haha

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