Oil soaked wood bearing
Practical Action
ceased to appear, the wood will Change to charcoal and the bearings will be ruined.
Rebore the centre hole to compensate for any shrinkage that may have taken place.
Place on a mandrel and turn the outside diameter to the required measurement that will
give the bush a press fit 1nto the hub.
Bore four equally spaced holes through the wall of the bush at its mid-point and fill with
lubricant .In general terms, the harder the lubricant the better, so animal fat, soap or
tallow are preferable although grease is an excellent alternative.
Figure 3: Bush bearing showing the four lubrication holes
The forty bush bearings made and tested at Zaria were 2.5" long by 1.550" outside diameter
with a 0.855" bore. They were pressed into 1½” seamless black iron Class C pipe, and
turned on a ½" pipe journal. The wood used was mahogany (being the most readily avail-
able) and rig tests with a loading of 100 lbs and a speed of 100-200 rev/min indicated
sufficient lubrication. These test conditions were chosen to simulate the working forces on a
7" gauge wheel of an ox-drawn plough. Tests performed on bush bearings without the four
radial lubrication holes again indicated sufficient lubrication.
Initial preparation
Saw timber into shape of an oblong block somewhat larger than the outside diameter of the
finished bearing to allow for shrinkage and bore being off centre. Bore a hole through centre
of block the size of the journal.
Oil level
Dehydration
Soon after submerging the bearing
blocks in hot groundnut oil, many
surface bubbles 25mm in
diameter, made from a multitude
of smaller bubbles will appear on
the surface.
As the moisture content of blocks
is reduced, the surface bubbles
will become smaller in size.
Heat source
When the surface bubbles are
formed from single streams of pin-
size bubbles, the dehydration
process has gone far enough. Stop
heating, and let blocks cool in the
oil overnight.
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