Sustainable Seed Systems

Introduction

At Washington State University Vancouver Research and Extension Center, we are using small-scale technologies to thresh and clean dry beans. It is a focus of our program to provide small-scale growers with cost effective and appropriate technologies that enable them to produce and market dry beans. The following are the steps and technologies that we use to thresh and clean dry beans.
Harvest whole bean plants or bean pods only, as you choose. Harvest beans before pods begin to shatter (pods split open, spilling beans onto the soil) in the field. However, plants must be sufficiently dry to thresh.

If necessary, dry plants or pods prior to threshing. Plants or pods must be sufficiently dry before they are placed in the thresher (described below) or they will bind up the thresher mechanism. Beans can be dried outside if weather permits. Hot, sunny weather for 3 days in Western Washington was sufficient to dry the pile of whole plants pictured below (Figure 1). Turn the plants 1-2 times each day to increase drying. If weather is cool or moist, beans can be dried inside using a box fax (Figure 2). Beans are sufficiently dry if the pods shatter, but are too dry if beans split.



Figure 1. Beans drying on vinyl tarp placed on a concrete pad (driveway) outside in hot, sunny weather in western Washington. Using this technique, beans were sufficiently dry for threshing in 3 days.
Figure 2. Figure 2. Beans drying inside a building with a box fan. Turn beans 1-2 times each day until beans are sufficiently dry for threshing.

Put beans (whole plants or pods) in the thresher chute, located at the top of the machine. Beans, crushed pods, stems and leaves will fall out the bottom of the thresher into the collection box (Figure 3). Beans tend to fall to the bottom of the collection box while plant debris tends to be on top. Scoop off the plant debris and discard. It takes approximately 5 minutes to thresh 100 plants with this technique.


Figure 3. Plant material including bean pods is placed into the top of the thresher (converted chipper-mulcher) and chopped up plant material including de-podded beans are collected at the bottom of the thresher.


Place the beans along with the fine plant debris into the top chute of the cleaner (pictured to the left in Figure 3). The beans quickly fall into another collection box at the bottom, while the remnants are blown away.

Remove by hand small rocks and dirt clods that fall into the collection box with the beans.

Small-scale Thresher

To make a bean thresher, we modified a chipper-mulcher, as designed by Allen Dong and Roger Edberg, I-Tech, PO Box 413, Veneta OR 97487. This design (public domain, no copyright) is posted on the U.C. Davis website, http://agronomy.ucdavis.edu/LTRAS/itech/thresh.html#shred. The U.C. Davis site includes several small-scale equipment designs. On the UC Davis web page, follow the link for ‘Conversion of a Leaf Shredder/Wood Chipper into a Grain Thresher,’ or for your convenience we have included the design at the bottom of this page (click here). Figures 4-7 show our thresher and include motor specifications that we have used.


Figure 4. Thresher made from a converted chipper-mulcher.



Figure 5. Thresher hammers are bolted together so that they beat plant material but do not shred or grind it.




Figure 6. Mesh keeps the plant material within the thresher until it is small enough to pass through. Smaller mesh would result in more finely chopped material while larger mesh would result in larger chopped plant material.

Figure 7. The motor (1.5 HP) used to operate the thresher needs to have its own cooling fan.

Seed Cleaner

The basis for our bean cleaner design is a Clipper Seed Cleaner. The Clipper seed cleaner unit we have on hand is an old one in poor working condition, but it provided the design idea for a winnower or seed cleaner that removes chaff and light seeds and debris from beans.

In our design (Figure 8), a large squirrel cage type fan provides the airflow, powered by a light duty electric motor with 1750-rpm CCW rotation. Airflow is very high, and is excellent for beans, although there would be a need to slow down the fan or block its flow for other seeds.

Sides of the chute were cut from ¾-inch plywood using an elongated version of the Clipper air chute as the template. The top and bottom of the chute are made with Luan or a similar thin flexible material such as sheet metal or plastic. The Luan (a thin pressboard material with smooth coating on one side) is stapled on top and bottom of the air chute sides, leaving a gap to drop seeds in (see Figure 8). Beans will fall out of the bottom, below the blower connection.


Creating a Grain Thresher

By Allen Dong and Roger J. Edberg, I-Tech, P.O. Box 413, Veneta, Oregon 97487
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 5 to 8 horsepower gas engines that rotate at 2800 or 3600 revolutions per minute (rpm). The modification requires:
Converting the free swinging hammers into rasp bars,

Reducing the rotational speed of the hammers (250 to 1000 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 (1725 rpm).

Materials:

A 5 horsepower, 2800 rpm “Roto-Hoe model 500” leaf shredder/wood chipper is used (Figure 1). Additional parts include:


4 2-inch C clamps (A),
6 5/8 x 3 inch bolts (B),
6 1/8 x 1 inch cotter pins (C),
1 5/8 inch inside diameter x 18 inch drip irrigation tubing or garden hose (D) as spacers between hammers, and
1 8 x 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 set 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 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 1 to 3 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.

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 are:

SeedsPounds of seeds per hour
Amaranth 66
Bok Choy 22 to 30
Oats 94
Pinto Bean 117
Soybean 81 to 127