Cider year 6: technical equipment notes

Um and pops inspect the grinder

Due to work-related time pressure, grinder and press development were limited this year, but a few important advances were made, primarily to the grinder. Readers will recall that in previous years, as the efficiency of the accompanying systems improved, the limited power output of the single rider powering the apple grinder became a limiting factor, both to output and to the quality of the experience. Accordingly, last year we borrowed a tandem bike and hooked it to the grinder. This made a dramatic difference in terms of grinding speed; the two pedalers working together could easily keep the system going at top speed no matter how fast the apples were fed. However, the user experience left something to be desired, as the mounting of the tandem bike was not perfectly rigid, leading to something of a precarious feeling. This was not helped by the fact that in a typical tandem setup the two cranks are locked exactly in phase by the timing chain, leading to significant surging, especially with platform pedals. At the close of the 2009 cidering it became obvious that the right way to do tandem power would be two single bikes, side by side.

So that’s what we did. Throughout the years the core drive system of the grinder has been the same: the bike is attached by the front fork to the grinder assembly, the normal drive chain is lashed out of the way, and a loop of bike chain is run forward from the large front chainring to a jackshaft on the grinder, which it engages via a freewheel, for approximately 3:1 increase in speed. A large sprocket on the jackshaft is separately coupled to smaller sprockets on the primary grinder and secondary crusher drums, giving approximately 4:1, such that speeds in excess of 1000 RPM can readily be achieved at the drums. A side-by-side configuration seemed preferable, for sociability and so both pedalers could see the action, and we desired separate freewheels for the two bikes, so one pedaler could keep going while the other stopped or swapped out another pedaler. (Or, at least that’s what I wanted; Holly rides a 10 mile commute on fixed gear and thinks freewheels are for sissies.) The easiest way to attach two bikes in parallel would be to extend the jackshaft out the left side of the grinder box, and attach another bike to the left of the original one. This presented a problem, since the large flywheel that Holly procured several years ago extended radially beyond the position where the shaft would pass through.

We solved this problem by moving the jackshaft outside of the grinder box, and supporting it with a long bar of aluminum. Holly machined two slick aluminum couplers with a 1.375-24 thread to couple the freewheels to the 5/8″ shaft, and I broached the couplers, machined keyways in the new 3′ long stainless shaft, and drilled and tapped the heavy aluminum bar to support the pillow blocks that allow the shaft to spin. In the new design, the aluminum bar bolts on to the outside of the plywood grinder box via tapped holes in the axial ends of the grinder frame extrusions, and the plywood is sandwiched firmly between the bar and the extrusion. The bar and shaft extended out perhaps 18″ beyond the left side of the grinder box, putting the two bikes approximately 32″ apart, which felt quite roomy. Once I got to Five Islands I set about assembling the whole contraption and trying to make it rigid; I used a bunch of scrap plywood, some 2×12, and a pair of short 4×6 scraps to extend the frame and support the shaft extension. In the end it worked great, though it looked a bit hokey. One of the brace plates that I put on doubled as a convenient shelf to put the bucket of apples on.

The experience of 2009 convinced us of the value of having chain tensioners in the drive loops, and so I extended the 4×6 posts that supported the bike front forks to mount a derailleur on each. In one case the derailleur I had mounted via a simple plate with a hole, and I screwed a hanger bolt into the 4×6 and sandwiched the plate between two nuts. The other case was more involved; the second derailleur I borrowed from one of the bikes, and it had a short captive shoulder bolt with an ultrafine M10x1 thread on it. I dealt with this by purchasing a suitable nut at Rogers hardware and welding it onto the head of a 1/2″ lag bolt, then grinding away the portions of the nut that interfered with the surrounding derailleur parts. This was a bit of work but it ended up functioning just fine. Here are images, first a detail of the left bike driveline:

Now the right bike detail:

As to the actual performance of the grinder, it was very smooth compared to previous years. The chain between the jackshaft and the grinder drums jumped off once, due to one of the set screws coming loose and the sprocket moving axially. We bent the tooth back straight, tightened up the set screw, and it worked fine after that. A spring-loaded idler would be a good addition to that loop, since there’s no convenient way to adjust the chain length by less than a tooth pitch – we just got lucky as it happened, and otherwise would have had to install an idler anyway. Beth inspired us to install a plexiglass spray shield that kept bits of apple from pelting the pedalers, this turned out to be a great addition. I also resolved to add a readily-removed clear plexiglass guard to keep fingers out of the chain drive system, which given the increasing numbers of kids around is asking for trouble.

Rolling out the press:

The press itself got minimal attention this year. As noted in an earlier post, Davis Carver of the Woolwich bike shop hooked me up with a stouter retaining ring for the cassette assembly on the drive wheel of the press bike, after the one from last year exploded. The hydraulic PTO had been repurposed last winter by Joshua and Kelsey as an electricity-generating exercise bike, so we quickly converted it back. I also fabricated and waxed five more press grates, this time out of Georgetown red maple, since the ones I made last year out of Georgetown basswood were marginal in strength. The press worked smoothly, and it was relatively easy to achieve as much as 2900 psi, where the system components are rated to 3000psi. This high pressure resulted in impressive yields, but it proved too much for the press cloth – on the first or second run the cloths tore against the press grates in the central region of the stack, and from then on we had to use a double layer of press cloth. Some of the older kids were really psyched to ride the bike on the press, and the amount of actual shaft work necessary is modest Someone suggested that we find a bike with a seat that can be adjusted all the way down to kid height. I think we’ll implement that next year; it would make a really impressive display of the power of bikes coupled to hydraulics.

The only real issue with the press was the impressive hydraulic kick that resulted when we opened the bypass to raise the ram after completing a press. The stack of spent pommace and the entire press assembly constitute a considerable spring, and when the bypass valve is opened to release the pressure, the energy stored in that spring is released as a rush of pressurized hydraulic oil into the return line to the bucket which serves as a hydraulic reservoir. In one instance, the kick from the release blew the return line out of the bucket, spraying a small amount of oil on the assembly. We washed the assembly down with hot soapy water, lashed return line to the bucket, and proceeded, resolving to open the valve more slowly. Later on, the same hydraulic pulse resulted in herniating the gasket that seals the low pressure oil filter on the return line, again generating a modest spray of hydraulic oil. Clearly this situation needs to be addressed; next year I plan to introduce an adjustable flow restrictor valve in the bypass line to limit the speed as the pressure on the stack is released.


2 Responses to “Cider year 6: technical equipment notes”

  1. Ian Derrington Says:

    Hi: I really like an appreciate you sharing info on your bicycle-powered apple grinder! I’m trying to make my own… more or less using your design.
    What Diameter shaft? ½”
    Where did you get bearings?
    Can you describe in more details on your grinding-drum with attached blads?
    Where did you get the ribbed squisher?
    What is the approx weight of your freewheel?
    Thanks for any info you can provide!!

  2. Ian Derrington Says:

    I just found a bunch of answers on your other page. Thanks for your efforts!

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