Mechanizing the Threshing of Soyabeans

This paper presents the work on developing a threshing machine through the process of reverse engineering. The main thrust was on improving productivity through the development of technologies that lessen the burden on small holder farms and reduce postharvest losses. The research work involved evaluating the performance of the Korean Buheung thresher, adapting it to the Zimbabwe industry and developing a prototype incorporating the changes and modifications as a result of the trials and the inputs from farmers. The result was a prototype developed using local expertise and materials.


Agriculture is very significant in Zimbabwean contributing about 60% of the inputs needed in the manufacturing sector. Zimbabweӳ demand for grains and legumes far outstrips its current production levels. The major challenge facing small holder farmers, to meet demand, is the lack of appropriate machinery. The developments between 2000 and 2008 re-configured the countryӳ agricultural and food sectors with changes in the farm size leading to increased number of farmers and relatively smaller sizes of farms. This has brought challenges and opportunities for agricultural development centered on a predominantly small holder production structure. Small scale farmers now constitute 75% of the farming population in Zimbabwe (MOA Statistics).

Small scale farmers predominantly harvest the soyabean with sickles and stacking them in the field to dry awaiting the threshing process which is also done manually by pounding the soyabeans with wooden sticks and winnowing using baskets.

With an increase in the production area under soyabean, the manual threshing process also tends to become more laborious. Inefficiencies from the manual threshing and winnowing also worsen the losses with damaged and broken grains resulting in low commercial value (FAO 2000). These problems can be addressed by mechanization.

According to Binswanger (1986), agricultural mechanization implies the use of various power sources and improved farm tools and equipment, with a view to reducing the drudgery of farm work. Mechanization is not an ԡll or nothingԠprocess. Levels and types of improved mechanical technologies need to be appropriate, that is, compatible with local, agronomic, socio-economic, environmental and industrial conditions.

The following could be said to be basic needs so as to improve the operating conditions in the farming.

  • A multipurpose machine for small scale operations
  • Simple design and ease of operation to mostly non-technical persons
  • Versatility for using in different farm operation
  • Affordability in terms of cost to small scale farmers
  • Locally available materials incorporated in design and fabrication of machines to reduce the manufacturing cost.


The Scientific and Industrial Research and Development Centre (SIRDC) in collaboration with the Rural Development Administration (RDA) of South Korea supported by the Korean African Food and Agriculture Cooperative Initiative (KAFACI) embarked on a project for small scale agriculture mechanization. A series of tests were conducted with Korean equipment with the aim of adapting them to the Zimbabwean local conditions.

Demonstrations were done at the farmersҠfields in Glendale and Concession with active participation from the farmers in obtaining their views on thee equipment. Performance evaluations comparing the use of the thresher technology and the conventional manual methods were also done. Trials at SIRDC farm and demonstrations on small holder farms were done to evaluate the work efficiencies.


The trials reviewed that the operational efficiency is improved by mechanization with resultant decreased post-harvest losses (table 1 below). The equipment was further evaluated based on both physical and technical attributes to determine the level of farmer satisfaction.

Table 1: Evaluation of work efficiencies

Conventional method- manual Mechanized
Operation efficiency 450 hrs/ hectare 14 hours per hectare
Output 200kg/ hr clean grains
% Losses 15% 3-5%

Using the Quality Function Deployment (QFD) (Khumi and Gupta) method, the comments from the farmers where incorporated in the new thresher design. The reverse engineering process was also used to transform the Korean thresher with attributes reflecting the Zimbabwean farmerӳ needs.

Table 2: QFD for the Thresher

Weight Weighted Score
5 Strong relation Customer Importance rating Drive- engine Threshing chamber Conveyance/ Elevator Transmission Mechanisms Weight Starter Material
3 Medium relation
1 Weak relation
Maintainability and Reliability 3 5 5
Ease of use 5 3 5
Affordability 5 5 3 5 5 3
Safety 3 5 5 5 3 1
Versatility 3 3 5
Efficiency 5 5 5 5 1
Mobility/ Portability 3 5 3
Durability 1 5 3 1 1 3
Importance weightage 79 70 58 66 29 26 45
Ratings 1 2 4 3 6 7 5

A modified version of the Korean prototype was therefore fabricated taking into consideration issues ease of use, affordability and efficiency as reflected in the QFD. The development process beginning with drawings from the Korean Buheung thresher and ideas from the farmers needs and results from the tests by SIRDC. For manufacturing, the 3D assembly design with the individual part drawings with dimensions and the bill of materials were generated using Solid Works and AutoCAD software taking the following into consideration:

  • Using fasteners (screws, bolts and nuts wherever possible for easy dismantling, maintenance and for corrective work
  • Provision for interchanging the screening sieve as well as drum so that it caters for other crops
  • Sloping system on the screw chamber allowing for easy flow of grain to outlet in the absence of the bucket elevator
  • Installing wheel to facilitate mobility of the equipment from one position to the other
  • Incorporation of power transmission from the power tiller or tractor


The resultant product a reverse engineered thresher prototype. The work on the application of these technologies in the cultivation of soyabean and the results were impressive. Commercialization of the equipment becomes a critical step towards contributing to supporting the smallholder farmer who cannot afford bigger sophisticated farming equipment. Models for transforming agriculture from subsistence to a commercial activity supported by these technologies are most appropriate.

Further work

The performance of the threshing machine is strongly influenced by the type of crop being handled and studies review that changing variables like the speed enable the machine to be multipurpose. This triggers the need for further testing with other crops including small grains (rapoko, finger millet), sugar beans, cow peas, maize and sesame. Small grains are increasingly becoming an important food crop in Zimbabwe especially due to the fact that they are adaptable to climate change variability, conditions currently prevailing in the country and region. The cultivation and post-harvest handling of small grains have been a mystery resulting in farmers disassociating themselves from the crops. Proposals for increasing the capacities of the threshing chamber whilst maintaining or reducing the weight and size of the equipment have to be further examined. The threshing capacity of the grains need to be increased as part of Further work and development on these machines are likely to produce many applications that are possible for integration in the mechanization efforts for the small holder farmer.


The study was carried out with the technical and financial support of the Rural Development Administration (RDA) of South Korea and the Korean African Food and Agriculture Cooperative Initiative (KAFACI) and the Scientific and Industrial Research and Development Centre (SIRDC)


  1. Binswanger H P (1978) Agricultural Mechanization A Comparative Historical Perspective University of Oxford UK.
  1. FAO (2006) Farm power and mechanisation for small farms in Sub-Saharan Africa, Rome, Food and Agriculture Organization.
  1. FAO (2005) Contribution of farm power to small holder livelihoods in Sub-Saharan Africa, Rome, Food and Agriculture Organization.
  1. Khurmi R. S and Gupta J.K: Machine Design. Eurasia Publishing house, 2005. 14th edition
  1. Ministry of Agriculture, Mechanization and Irrigation Development, Government of Zimbabwe
  1. Research and Development of Agricultural Mechanization Technology in Korea, 2011, The Department of Agricultural Engineering, National Academy of Agricultural Sciences, RDA

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