Results are In! Re: moisture in wool or wood.

[Ron Nossaman]

>Not meaning to be picky... grin.. but I will... how does Terrys experiment 
>yeild
>any information about the amount of compression that would be exerted on the
>centerpin ? I mean the drill bit is really hard and aint going nowhere... a 
>felt
>bushing would give a bit, and I dont think we are exactly clear on just how 
>much
>pressure it takes to cause a centerpin to get sluggish.
>
>Richard Brekne


Nonsense! Of course you're meaning to be picky, Richard. 

My point was that it doesn't take much of an interference fit with hard
maple to where you couldn't get the rod in at all by hand, so the hole
didn't get all that much smaller, or possibly didn't remain round. I
assumed that the couple of thousandths" of size decrease wouldn't make a
heck of a lot of difference to the pin tightness because the bushing cloth
compresses, especially if it was just out of roundness of the hole. Since
Jim hasn't yet posted his results from soaking bushing cloth, and no one
else has apparently even gotten any wet, I spent the last hour in the shop
exploring this a little from the bushing cloth side.

Using a dial indicator snap gauge I put together a while back for measuring
string diameters quickly in the piano, I clamped it in the vise, and cut
some short pieces of bushing cloth to test. I left the cloth pieces in
place in the gauge, without disturbing it other than wetting it with a mild
detergent solution, through each test trial. 

Unweighted, with just the gauge spring clamping the cloth, the initial dry
measurement was 0.0355". Wet, after 5 minutes, it measured 0.0375", for an
expansion of 0.002".

Weighted with 150grams, dry measurement was 0.034". Wet, after five
minutes, it measured 0.0355", expanding 0.0015".

Weighted with 211g, dry measurement was 0.0338". Wet, after five minutes,
it measured 0.035", expanding 0.0013".

Weighted with 211g, double thickness, dry measurement was 0.067". Wet,
after five minutes, it measured 0.0698", expanding 0.0028". 

Note the relative correlation to initial compression by the weight, and
expansion. Note that the expansion is between 3.5% and 4.5% of the
compressed thickness in all cases. I would expect the expansion percentages
to change with different batches and densities of cloth. Nevertheless, this
would seem to indicate that bushing cloth expands against and
proportionally to resistance.

Now you tell me how Terry's test tells us what we need to know about the
size and shape of the hole, and I'll explain to you how it fits with my
results to explain center pins tightening with humidity increases, if you
really think it's necessary at that point.

Ron N