Like almost everything else, what woods are best for bearings depends 
entirely on who what where when and why.   Ebony and lignum vitae were and 
are commonly used in industrial applications for water immersed bearings. 
It is not so much their hardness as their natural oily qualities (preventing 
rot) that make them useful.  Lots of vertical shaft turbines from the 1800s 
have lower seat bearings and adjustable (and replaceable) side-travel blocks 
of those woods, and top bearings too if the turbine was totally immersed.

However, the 1876 pack horse era grist mill I restored in Keremeos, BC still 
had some of the original bearings for the water wheel, line shafts and 
machines.   The water wheel, fitted with iron gudgeons and their 4" shafts 
used Babbitted bearing blocks, but the first counter shaft had a 3" gudgeon 
shaft riding in a wooden bearing block made of Douglas Fir.   Neither was 
supposed to be wet, simply oiled.   The water wheel (10 rpm) weighed a 
couple of tons while the first counter shaft only had to spin at 20 rpm with 
less than 50 lbs of weight.on each of its bearings.   Inside the mill, 
succeeding counter shafts and the main line shaft rotated at progressively 
higher speeds but with either wood (Fir) or Babbitted iron blocks depending 
on the gravity loads or side thrusts to be accommodated.   The fastest was a 
700 rpm counter shaft and idler pulley that used fir bearing blocks for a 2" 
steel shaft.   Caked oil on the wood showed the attentive care given to this 
one, but the shaft still fits the hole quite nicely even after its dozen 
years of historic use.  I would love to get an analysis of the oil residue 
to see what they used there in the 1880s.

The reason I mention all this is to illustrate that in that pack horse 
lifestyle setting, efficiency was critical.   It was two hundred miles over 
the mountains to the next town and a five month sailing voyage to Britain 
for spare parts, so you had to make efficient choices about what to carry in 
and what to make on the spot out of local materials.   (Actually I 
exaggerate a little.  By then it was only three months by ship to Britain 
and two days to San Francisco by fast steamer - but still at least three 
weeks on the trail to get to the ship.   The Hudson's Bay Company commonly 
sent two pack trains a year into the region with supplies.   There were even 
some wooden shafts, carved to hexagonal shape with 4" diam. cylindrical ends 
for the bearings.   They were set into wooden bearing blocks.   Speeds about 
60 RPM with light vertical loads.

A wood technologist here who performed a detailed analysis of every major 
item in the mill, commented that he was surprised to find Western Red Cedar 
used in many applications there, but that the wood structure in those parts 
was much more dense than usual.  He mistakenly said that the wood had 
perhaps become compressed due to the loads, but was wrong about than, not 
really understanding how the machinery worked.   But he also said that the 
unusually dense cell structure might also have been caused if the wood had 
been exposed to fire.   As a living history restoration woodworker, that 
make a lot more sense.   The original builder of that mill performed some 
amazingly sophisticated work, and I would not be surprised if he either 
selected wood for those parts from timbers that had experienced forest fire 
or perhaps intestinally hardened the wood by fire to give it the quality he 
needed for those particular parts.   Heck, we still do that with fence posts 
where they are going to touch the earth.

The important thing about axles and bearings is to protect the precious bits 
with expendable and replaceable mating parts.   Shafts are usually a lot 
more important and costly than the bearings, so the bearings will always be 
softer or less wear resistant.  Hence Babbitt sleeves in iron blocks too. 
With slow speeds and low weights, even fir works just fine as long as you 
keep it oiled so it doesn't catch fire from friction.   It is all about 
those three factors of friction, pressure, grip and speed.   In our modern 
age of alternating current and high speed tools, it is easy to forget how 
slow and quiet things were in those good old days.   The only ear protection 
needed might be ear muffs against the cold.  The grist mill when operating 
was/is like a little chamber music concert of delicate sounds and clicks. 
When in tune, it sings to you about its pleasure of smooth operation, 
allowing you to hear all the diverse voices in harmony; but it might just as 
well groan with dismay at feeling friction.

cp in bc
(still grinding)



----- Original Message ----- 
From: "Gabriel Orgrease" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, February 09, 2008 2:47 AM
Subject: [BP] wood bearings



What woods are best used for bearings?

crosspost from hurdy-gurdy list

"Even if this one is not really linked to the hurdy-gurdy: A friend of
mine owns a water mill from baroque times and the bearings of the water
wheel (he´s actually replacing it) are traditionally made from apple
wood. Not really what I would have used but exactly what he found and
what he was told from several experts and museums here. But I don´t
think that it´s a good idea to transfer this to the hg - the humidity is
hopefully at least a little different "

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