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MMD > Archives > September 1999 > 1999.09.06 > 12Prev  Next


Lubrication Testing Machine for Wooden Crank Rods
By Bill Finch

When I rebuilt my first band organ in the early 1960's I ran into pump
sticks for the first time. I really didn't know how to lubricate this
metal-to-wood bearing surface.

I asked three very experienced machinists what to do.  They each
had the same answer: "Wood in contact with metal is essentially self
lubricating."  This is a wisdom which had been passed down to them
in the late 1930's, at the tail end of the mechanical era.

I tended to doubt their advice but they all insisted that this advice
was correct and in line with the traditions that they had learned as
apprentices in Germany, Denmark and Austria.

To test their argument I built a device with four pump sticks driven by
an electric motor turning an automotive (MG-A) crankshaft.  The sticks
worked against the resistance offered by paddles immersed in a tub of
water.

One stick was unlubricated oak.  Three sticks were sugar maple.  One of
the maple sticks was unlubricated.  A lithium-based grease and a molyb-
denum based grease were used to lubricate the two other maple sticks.
The water supplied a sinusoidal force with a peak of 34 pounds.

This curious looking kinetic sculpture ran at 80 rpm for a little over
three years.  It drew many comments.

After about 1.25 million revolutions the maple bearing surface
elongated by 6 mils for all of the maple sticks and 11 mils for the oak
stick.  The lateral non-weight bearing surface increased by 2 mils for
the maple and 1.5 mils for the oak.

The benefits of lubrication proved to be neutral compared with the
unlubricated sticks.  The oak was slightly more deformed by force and
slightly less worn by friction.  The maple had a slightly higher
friction wear but less deformation by force.

In spite of this experiment I still lubricate pump sticks.  I use gun
oil mixed with molybdenum disulfide powder.  I do this after about 10
hours of operation because it makes me feel better.  I suspect that any
lubricant would do as well: wax melted in kerosene, lamb fat, beef
tallow, commercial lubricants -- I doubt that it matters.

Two words of caution: don't let it the lubricant on the bellows, and
don't let it build up enough to attract grit.

Bill Finch


(Message sent Tue 7 Sep 1999, 02:50:14 GMT, from time zone GMT-0500.)

Key Words in Subject:  Crank, Lubrication, Machine, Rods, Testing, Wooden

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