Motorizing the Apple Grinder

As described in more detail in another post, my cider press has a wonderful array of heavy cast iron gears and a flywheel to help make hand cranking the grinder portion easier. Unfortunately easier is relative to the time of production, and for those of us who do not operate an array of large human powered machines on a daily basis (as was the case when this press was built in the early 1900’s) it was still, quite bluntly put, hard and tedious work to grind more than a bushel or so of apples. With substantially more than that to press this year and less people to do it, the time had come to try and motorize the grinder.

Step 1 was to find a motor. A friend had an extra ¾ hp variable speed blower motor available and that was the first choice, but it was designed to be face mounted on a direct connect blower chassis and I was unable to find a suitable mount to be able to use it. In addition, it had an open frame and I was concerned that the inherently messy process of grinding and pressing apples might not work very well with a non-enclosed motor. Despite that, it seemed to be the only motor available so I started going through my shop to try and find some way of mounting it. Suddenly the obvious answer hit me and my ½ hp bandsaw motor picked up a new job description, though I did have to reverse the rotation to fit the new role – fortunately the motor connections were designed to make this an easy process.

Step 2 was to find a way to drive the grinder. I knew that the grinder was designed to be hand cranked, and based on past experience that the most we had been able to do was about 1 turn a second on the crank handle, which through gearing equated to roughly 150 rpm at the grinder. While the grinder could probably cope with higher speeds, some limitations were set by the fact it had plain cast iron bushings, was pretty much unbalanced, and did not have any capability for precision alignment, all of which throw up red flags against high speed operation.

The motor delivered 1750 rpm and already had a fairly small pulley, so I needed to find a fairly large pulley to fit on the existing 7/8 inch direct drive shaft and bypass the gearing. The first option was to use the existing flywheel, which seemed to have been cast with a crowned rim to provide a flat belt drive option. Unfortunately when I looked more closely I realized that that may have been the intent, but the execution was somewhat less than ideal and substantial machine work, for which I didn’t have the necessary tooling, would be required to make it suitable. In addition, I only had V-belts around me to work with. A trip to a local farm machinery supply shop yielded no acceptable options; the best available was a 12 inch weldable steel pulley but they did not have a suitable weldable hub and were unable to source one in the necessary timeframe.

With no other options readily presenting themselves, it was time to see about making a pulley. Back in the shop, I found a wooden disk in my scrap pile about the same size as the weldable pulley and figured that I could either make a wooden hub or find a way to attach it to the existing flywheel on the grinder. After mounting it on a faceplate I used the lathe to cut a groove corresponding to a V-belt I had lying around, then bored a 7/8 inch hole for the shaft.

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Step 3 was to mount the motor and test the system. My thought had been to cut a recess in the pulley for the flywheel hub and then use some steel strapping to make bolt-through clamps to attach the pulley to the flywheel spokes. When I looked in detail I realized again that the casting quality of the flywheel was such as would have made this a very time consuming effort, so as a prototype compromise I drilled a couple of holes and used some fence wire to tie the pulley to a couple of the spokes. The belt was a bit long, so I needed to slide the motor back beyond the frame of the cider press to accommodate, which called for building an extension. Again as a prototype compromise I looked around and found some clamps, a shop stand, and a piece of scrap wood to knock something together. For the initial run I left off the upper portion of the grinder so I could see everything.

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Once hooked up I gave it a few rotations by hand to make sure that everything was free to turn, borrowed the switch from my router table, plugged it in and gave it a brief shot of power, half expecting the motor to stall or everything to fall out of alignment. Instead the motor started smoothly, the rollers began turning and all looked good. After a quick check to confirm all was good I turned it on and let it run for several seconds. It seemed a touch fast but otherwise good, so I mounted the top portion and gave it another quick check. With a few extra components involved it was a bit noisier but otherwise good, so I decided to toss an apple in and see what happened. The results were impressive as the apple essentially exploded, however at the speed the grinder was turning the angular momentum overcame gravity and rathar than falling from the chopper into the crushing roller the bits of apple nearly all were swept around the bottom of the turn and were thrown up and out of the hopper, making quite a mess.

Knowing that the system generally worked, a few calculations identified that with the size of the prototype pulley the chopper was turning at around 500 rpm and that a pulley diameter of around 18 inches would probably be about right. Once again the scrap pile proved to be handy and a piece of ¾ inch plywood of roughly the right size came to light. As the bandsaw motor was still out on the press I used multiple small cuts on the tablesaw to nibble the square into something resembling a circle, mounted a faceplate, swung the lathe head (the first time I have used that feature, and it was very handy to have) and repeated the pulley making process. With the head swung I was unable to use the lathe to drill a centered hole, so after marking the center with the lathe spinning I used a drill with the lathe off to drill as close to a centered and perpendicular hole as I could.

The larger pulley required a few changes to the motor mounting on the press and also required removal of the large cast iron gear which was not being used but I had left on during the first trial to act as an additional flywheel. Once these changes were made the system was again tested, this time with much better results. It was still a touch faster than I wanted, but I was able to find a slightly smaller pulley for the motor which brought the chopper speed down to under 200 rpm and the system was ready to use. The only downside to the smaller drive pulley is that with the larger pulley the system would start even with apples in the hopper, but the smaller pulley has just a touch too tight of a bend for the belt I am using to keep contact and if the hopper is not empty to start with the belt will slip. The lower wear and tear and mess which comes with the slower operating speed seems worth the operational restriction.

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Without the motor it seemed to take 2 people around 10 minutes to grind a bushel of apples with the crushers set at around 1/8 inch gap, with the motor it takes one person around 4 minutes to do the same with the crushers set at a much more effective 1/16 to 1/32 inch gap. The limiting factor has shifted from the strength and stamina of the person turning the crank to the actual loading of the hopper and distribution of the pomace.

A slow motion video of the grinder in action at various speeds is available here: https://youtu.be/rG3dJDiLWhQ

 

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2 Responses to Motorizing the Apple Grinder

  1. Chuck says:

    I am making a similar conversion on a Red Cross press that I restored a couple years ago. Would very much like to talk to the author of this article to pick his brain. My estimate is that hand cranking produces about 250 rpm at the grinder and crusher drums. My flywheel is 15.5 ” and I have machined a v belt groove into it. I also replaced the iron bearings on the rollers with impregnated bronze bushings. The grinder drum would be much more problematic to improve with more modern bearings so that remains one of my limitations. So, What is the ideal RPM I should target? Is 1/3 HP adequate? Any other thoughts?

  2. rurikia says:

    With the geometry of my grinder and crusher components I’ve found that it works pretty well at a touch under 200 rpm at the grinder (off the top of my head I think it’s around 190 or so), but I’d prefer to go a touch slower. The main issue I have is that with larger apples the higher speed causes them to bounce on top of the grinder rather than get pulled into it. If 250 rpm at the working end works for your geometry than something around there should work as a reasonable starting point. As for the motor, I know mine works well with a 1/2 HP though I do have to start with an empty hopper and add apples once it’s spinning or the belt slips.

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