[Harp-L] broken Seydels

Vern jevern@xxxxx
Tue Jul 3 19:14:09 EDT 2018

> On Jul 3, 2018, at 6:59 AM, Joseph Leone <3n037 at xxxxx> wrote:
> …..Btw: cold water was used because it not only caused the reed plates to contract, it also cause the reeds to contract MORE. Why? Because they were much thinner brass and
> more sensitive to temperature. Ergo, tighter reed slot tolerances…….. 

 Although brass parts do expand and contract with the rise and fall of temperature, the magnitude is much less than you suppose.

See http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thexp.html  

The thermal coefficient of expansion of brass is 11 parts-per-million per degree F.   If cool water dropped the temperature of the plate and reed by 20 degF,  a  .75" long reed or slot would change its length by only  
11 x 10^-6 x 20 x .75 = .00017”  The width of the reed or slot would only change by 10^-6 x 11 x 20 x .08 = .000018"  That is insignificant.  

Because the thermal conductance of brass is very high,  the reed and plate would be very near the same temperature within seconds and the slot tolerances would not change as much as 11 x 10^-6 x 20 x .004 = .00000009”

Please check my arithmetic.

The amount of moisture in a wooden comb will definitely affect its dimensions. However, changes of temperature will not perceptibly affect the dimensions of the metal reeds and slots or the performance of the harmonica.


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