Oil soaked wood bearing
Mandrel
Practical Action
Shrunken block
Figure 5: Shrinkage takes place once the blocks have cooled
Finishing
Re-drill centre hole and place shrunken oil-soaked bearing block on mandrel and turn to the
desired size.
Figure 6: Cross section of the finished
oil-soaked wood bearing showing
grease reservoir holes.
On heavy equipment such as ox-carts or where it is not possible to push the axle through a
bush bearing, the split-block bearing provides a more practical solution. It is simple to fit
and replace, and if wear takes place the two halves can be changed around. After further
wear, the life of the bearing can be extended by removing a small amount of material from the
matching faces. A simple procedure was devised by the GRZ/ITDG Project at the Magoye
Regional Research Station in Zambia for the production of such a bearing, again using an oil
soaking technique. The timber in this case was teak, and used engine-oil provided a
satisfactory alternative to ground nut oil. (Coombs & Pearson, 1974)
Reduce the timber to a square cross-section and out length-wise into two halves.
The two halves of the bearing must be clamped firmly together for the drilling operation.
It is most important that the hole for the axle is bored exactly square through the blocks.
For the best results an electric powered pillar-drill should be used al though a hand
powered pillar-drill would be quite satisfactory. If neither of these is available, a jig
would have to be made to keep the drill bit in line. After drilling, the two halves should
be tied together to keep them in pairs.
For soaking in oil an old 20-litre (5-gallon) drum is needed. Fill it three-quarters full with
used engine-oil and bring to the boil over an open fire. Great care is needed when
handling the drum of hot oil. Lift the drum off the fire and carefully place the pairs of
bearings into the hot oil. Put a brick on top of the last pair to stop them floating, and
leave the drum and contents to cool slowly overnight.
The split-block bearings measured 150mm x 15Omm x 15mm with a 38mm diameter bore.
They were field tested for reliability by installing them on ox-carts fitted with iron or
pneumatic wheels and carrying loads of up to 2 tons. A radial clearance on ODs of these
assemblies of about 1mm was found to be essential. If carefully run in at low speeds (ox
work), the clearance is increased to 1.5-2.0 mm and the bearing surface attained a highly
polished glass-like appearance. Raving reached this condition it was round capable or
withstanding journeys or a few kilometres at higher speeds (Landrover towing).
A sort pine-wood oil-soaked bearing was tested as an alternative to the hardwood bearing, and
this also gave satisfactory performance but might have a shorter lire. For lower load, lower
speed applications such as the seed-drive mechanism on a small planter, a smaller one-piece
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