[Harp-L] Re: Reed Measurements

["'Dr. Michael J. Marino, DC'" <m.marino@xxxxxxxxxxxxxxxxxxxxx>]

ÂCrazy Bob,

Reed measurements are something I deal with weekly to match reeds to
the instrument and also in sorting reeds when salvaging them from
damaged harps that are beyond the reasonable ability to repair (cracks
showing in 25-30% of reeds can be a reason). The measurements are
common and follow known progression depending on a few variables (type
of metal, desired length of reed and such). You will find that most
reeds have a tolerance for tuning of about two to three notes each
side of the desired note. Also when tuning or making a reed you need
to take into account heat as that changes the structure of the metal
and in both brass and PB Bronze causes a brittling to take place (this
is why when using dental bit to tune you take a little at a time and
let the reed settle). 

If i remember correctly you are looking at setting up something
similar to a key cutting machine to mill the blanks from the stock
metal. Depending on how you set that up it could work and be very
exact but also a bit time consuming on getting the blanks ready or it
could eat up a lot of metal for not much return. Henderson Harmonicas
has shown a very useful approach by going away from the transverse
ground reed to a longitudinal milled reed. That removes a good bit of
stress from the movement of the reed and could possibly add some
strength as well (I say could as don't have solid data either way). 

As far as tolerances go, most production harps gap between reed and
slot of .05mm/side of reed. This is pretty much true with all of them
in the chromatic family (I have found no exceptions yet, still
looking) That gives you a functional tolerance of about .0125mm in any
dimension of the reed tongue that flexes. Which should insure that the
reed will NOT hit the sides of the reed slot.

Tuning a reed in the gross is ratios of root to tip across the
cantilever of the reed length. In reality there are sections of the
reed (even small harmonica reeds) that will tighten the root frequency
desired, that will strengthen the third or the fifth and clean up some
of the natural occurring secondary frequencies of the reed. Also the
belly of the reed not only needs to have a mild bend to it, it also
needs to be a bit thinner then the root or tip where possible (some
reeds don't follow this rule and are almost exclusively in the upper
octave of a Chromatic).

Last I knew Seydel does sell individual reeds as pack sets, that might
have changed though. To get a good base find some old harmonicas and a
digital vernier callipers and start measuring and writing down what
you find for each maker (there is some over lap but not as much as you
think). from there it is simply setting up a data base and you got it
set. I am still adding to my data base and it has taken a good bit of
time and effort to get it done. Good luck

Michael Marino

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Sent:Wed, 18 May 2011 14:13:18 -0400
Subject:Harp-L Digest, Vol 93, Issue 41

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