Public Domain Thresher Designs (Guide to Backyard Farming)

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The two main components of the I-Tech rice huller are a hand mill/ flour mill or grain grinder and a rubber-faced disk made from a rubber disk, a steel washer for mounting the rubber disk on the hand mill, and cyanoacrylate glue ("super glue" or "krazy glue") to attach the rubber disk onto the steel washer.

The stationary disk (A) is removed and replaced by a rubber faced disk (B). Turning the auger handle (C) presses rice grains between the rubber-faced disk (B) and rotating disk (D), and then they are rolled out. The soft rubber disk allows the hulls to be removed with minimal damage to the rice kernels. Natural (gum) rubber is used for the rubber disk because it has better abrasion resistance than synthetic rubber. (The " Corona" hand mill is available from R&R Mill Co., 45 West First North Street, Smithfield, UT 84335, USA.)

Short-grain rice can be hulled at a rate of 200 g/min. The percentage of rice hulled varies from 75% to 99% depending on the rice cultivars, the spacing between the stationary rubber disk and the rotating abrasive disk, and the uniformity of spacing between the disks. A tin-plated steel burr disk may produce a black gum residue when hulling rice, until the tin is worn off. No black residue was found when using a cast iron disk or stone disk.

---------- Standard grain grinder modified to husk rice and spelt.

The grain huller also hulls millet (Panicum miliaceum), sesame (Sesamum indicum), and spelt wheat (Triticum spelta) as well as removes saponins from quinoa (Chenopodium quinoa). To "wet" hull sesame, soak the seeds in 1% (w: v) lye (sodium hydroxide) solution for 10 seconds to 5 minutes, then rinse with water and 1% solution of acetic acid (Shamanthaka Sastry et al., J. Am. Oil Chem. Soc. 46:592A, 1969; Moharram et al., Lebensmit. Wissen. Tech. 14:137, 1981). A steel burr disk is preferred for wet hulling sesame, while a stone disk is preferred for hulling spelt wheat. A hand-operated rice huller has a (A) stationary disk, (B) rubber disk, (C) handle, and (D) rotating disk with auger . Remove the stationary disk and replace with the rubber-faced disk.

In the United States, the C.S. Bell model 60 (cost: $325) and the Corona hand mill (cost: $40) represent two ends of the spectrum of hand mill quality. For serious hulling, the C.S. Bell is the better choice. This mill weighs 54 pounds, its auger shaft is supported by two bronze bearings with oilers, the grinding disks self-aligns and the mill can be motorized. The bronze bearing with oilers allow the shaft to rotate at 300 rpm without heating up (C.S. Bell, PO Box 291 Tiffin, OH 44883, phone 419-448-0791).

The Corona hand mill weighs 14 pounds, it has no bearings, the grinding disks do not self-align, and the mill cannot be motorized (R&R Mill Co., 45 West First North, Smithfield, UT 84335, phone 801-563-3333).

Conversion of a Leaf Shredder/Wood Chipper into a Grain Thresher

This invention was declared public domain August 1994, a gift to humanity.

A portable, engine-driven thresher can be made by modifying a leaf shredder/wood chipper or a hammer mill. Small shredders/chippers use five to eight horsepower gas engines that rotate at 2,800 or 3,600 revolutions per minute (rpm). The modification requires converting the free-swinging hammers into rasp bars, reducing the rotational speed of the hammers (250 to 1,000 rpm on a 12-inch diameter hammer arms), and altering the discharge port to allow smaller , threshed material to pass through a 3/8 to 3/4 inch screen while retaining larger materials.

(Optional) If electricity is accessible, the gas engine can be replaced with a 1/2- to 3/4-horsepower capacitor start electric motor (1,725 rpm).

Materials: A five horsepower , 2,800 rpm "Roto-Hoe model 500" leaf shredder/wood chipper is used (see picture following the text).

Additional parts include

6 5/8 × 3-inch bolts (B), 6 1/8 × 1-inch cotter pins (C), 1 5/8-inch inside diameter × 18-inch drip irrigation tubing or garden hose (D) as spacers between hammers, and 1 8 × 10-inch sheet metal or cardboard (E) to block the slotted portion of the leaf shredder/ wood chipper exit port.

Modification: The Roto-Hoe shredder has six sets of three free swinging hammers (F). Convert the six sets of hammers into six rasp bars as follows: Cut the 5/8-inch tubing (D) in segments to fit between the free-swinging hammers (F). Tie the free-swinging hammers (F) together by inserting the 5/8-inch bolt (B) into the hole of the first hammer , followed by a segment of tubing (D) as a spacer , then another hammer , followed by a second segment of tubing, followed by the third hammer . Drill a 5/32-inch hole on the threaded portion of the bolt that protrudes from the third hammer .

Reassemble the bolt, hammers, and spacers together and lock the bolt in place with the cotter pin (C) installed in the 5/32-inch hole.

This assembly constitutes a rasp bar . Repeat the above procedure and tie together the remaining five sets of free-swinging hammers.

Manually rotate the rasp bars and check for clearance between the rasp bars and the walls of the threshing chamber . If there is insufficient clearance, adjust the bolt position, grind the bolt head, or cut the bolt length to obtain the necessary clearance between the rasp bars and the walls.

The Roto-Hoe shredder exit port consists of a slotted section and a 3/4-inch diameter punched-hole screen. Use the sheet metal or cardboard (E) and C clamps (A) to block the slotted portion of the exit port (G). The threshed grain exits through the 3/4-inch holes.

Start the engine and spin the rasp bars. Again, check for clearance between the rasp bars and the walls of the threshing chamber. If there is a knocking sound, grind the bolt down to obtain the necessary clearance.

Operation: Start the engine and spin the rasp bars. Dried plant materials with vines, stems, and leaves are fed in batches through the hopper . After threshing for one to three seconds, open the top door to eject the longer vines, stems, and leaves that have not been chopped up. Seeds and small bits of plant material exit through the punched holes at the bottom. The mixture of seeds and plant material must be separated after threshing.

--------- Leaf shredder converted into a grain thresher.

The 3/4-inch diameter holes in the exit port are suitable for larger seeds (e.g., beans) and seeds with loosely attached husks (e.g., wheat, bok choy, and amaranth). Small seeds and seeds with tight husk or pods (e.g., barley, clover , and radish) require smaller diameter exit holes to retain the larger unthreshed materials while passing the smaller threshed grains. This can be achieved by attaching a screen with smaller openings under the 3/4 inch diameter punched holes.

Larger seeds crack easier than smaller seeds. Reduce the rasp bar speed to decrease the percentage of cracked seeds. Use a larger pulley (H) and/or reduce the engine speed to achieve the desire rasp bar speed:

250-400 rpm for beans and large seeds 400-800 rpm coriander, radish, sunflower 600-1400 rpm wheat, oats, barley, rice, and small seeds Typical threshing rates (pounds of seeds per hour):

Amaranth 66 Bok choy 22 to 30 Oats 94 Pinto bean 117 Soy bean 81 to 127



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Updated: Tuesday, February 16, 2021 11:14