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INTRODUCTION

Rotating, oscillating and sliding bearings perform vital functions in all types of machinery from wheelbarrows to jet engines. Many types of bearings are in use:

1. Ball and roller (anti-friction) bearings
2. Metal-toMetal journal bearings under conditions of boundary or hydrodynamic lubrication.
3. Metal-toPlastic bearings
4. Hydrostatic bearings
5. Air bearings

In the 3^rd World, it is not uncommon to find wheelbarrows, handcarts, and oxcarts whose journal or roller bearings have worn out and have not been replaced due to lack of the spare part, lack of cash for the spare part, or lack of workshop facilities or the knowldedge for repair.

One centre for the innovation and production of agricultural machinery in Tanzani, the Tanzania Agricultural Machinery Testing Unit (TAMTU), has therefore for some years been designing and producting oxcarts, oxloughs and oxplanters using wood/steel journal bearings, and wheelbarrows and maize shellers using wood/wood journal bearings. The timber they use uis usually "Mvule" , impregnated with old engine oil.

Wood/Steel journal bearings are used on the shaker trays of some combine harvesters produced in "Developed" Countries, and at least one farmer in Tanzania is said to have used wooden bearings on his tractor-mounted disc plough.

On investigating the literature on wooden bearings, an almost complete lack of scientific data was found, and it was decided to mount a project on this topic at Morogoro (University of Dar es Salaam / Sokoine Agricultural University). The work was done by Katule during his final undergraduate year at Morogoro, supervised by Weir.