Oil soaked wood bearing
Practical Action
Types of bearing
Bush bearing
Split-block bearing
One-piece block bearing
General remarks
H.S.Pearson (1915) has suggested that as a general rule-of-thumb guide to the size of timber
needed for the bearing, the axial length of the bearing should be at least twice the shaft
diameter. For example, for a 25mm diameter axle, the bearing should be at least 5Omm
long. In the case of the block bearings, the thickness of bearing material
Figure 2: Split-block bearing
The drilling of radial holes for lubrication purposes is only recommended by Pearson for the
bush type of bearing. He found that if lubrication holes were drilled in block bearings not
only were the bearings weakened but also the holes acted as dirt traps.
The bearing should be located whenever possible in a position where falling dirt will not direct
enter the bearing. For example, if the axle is carried in bearings mounted under the floor of a
cart instead of a fixed axle with bearings at the hub of the wheel, then dirt falling from the
rim of the wheel will not fall directly onto the bearings.
If the bearing is expected to take side-thrust, large flat washers must be used, the one next to
the end of the bearing being free to rotate on the shaft. The bearing surface of the shaft
should be perfectly round and smooth and polished in appearance.
How to make the bearings
Available timber often has rather doubtful self-lubricating properties and high moisture
content. In this instance, a simple procedure for making an oil-soaked bush bearing has been
devised by the Industrial Development Center, Zaria in Nigeria. Excess water
is removed and subsequent shrinkage prevented.
Reduce the timber to a square cross section and bore a hole through the centre the same
diameter as the journal on which the bearing will be working.
Place the blocks into a metal container of commercial groundnut oil and keep them
submerged by plac1ng a brick on top. Raise the temperature of the oil until the water in
the wood is turned into steam -this will give the oil the appearance of boiling vigorously.
Maintain the temperature until only single streams of small pin-size bubbles are rising to
the surface of the oil. This may take anything from 30 minutes to 2 hours depending on
the moisture content of the wood.
Remove the heat source and leave the blocks in the
oil to cool overnight if possible. During this stage
the wood will absorb oil. If the temperature of the
oil is allowed to get too high after the bubbles have
Be very careful if you need to
handle the container whilst it is
full of hot oil.
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