[Harp-L] Re: Embossing and Chamfering

["Rick Epping" <rickepping@xxxxxxxxx>]

Hi folks,

Thank you for your responses.

Regarding embossing:
The tool for fine embossing is made from a length of 1.8mm hardened tool
steel rod, the end ground to a 20 degree angle.  I gave it the shallow angle
so that it could fit between the reed and the slot, flat side against the
reed and radius against the slot edge.  It is for embossing and not
chamfering; there is no removal of material involved.  As I approach the
rivet end of the slot edge while embossing, I gradually pull the tool out
from under the reed so that it does not force the reed up enough to affect
its offset.  Before reaching the rivet end I will have removed the tool
entirely from under the reed so that the tip of the tool runs against the
reed edge as a guide for embossing the section of slot edge closest to the
rivet.  I use no guide other than the reed itself.  The reedplate is mounted
on a light box to illuminate the reed/slot clearance during embossing.

I lower the reed into the slot after embossing by pressing a fingernail on
the reed near the rivet end, slowly rotating the nail away from the rivet as
I do so.  Exactly where and how hard to push without damaging the reed is
determined mostly by feel, not by sight.

Regarding chamfering:
I push the chisel forward to cut away the top edge of the reed, as a chisel
and not dragged backward as a scraper.

Correction: I use a .002" feeler gauge, not a .001" gauge, to support the
reed during chamfering; a .001" gauge is not stiff enough to provide
adequate support.  I do use a strip of .001" feeler gauge in the tool for
clearing slots embossed too closely.

I do not chamfer all the way to the bottom edge for three reasons:
1. It would be difficult to adjust the reed curvature and offset of a fully
chamfered reed so that its narrow edges would would align at the same moment
during oscillation with the narrow slot edges created by embossing.  Leaving
some width to the reed edge helps assure a close air seal at the moment the
reed passes through the slot.
2. Chamfering all the way to the bottom edge of the reed runs the risk of
cutting away some of the edge altogether, which would cause air loss and a
lowering of compression.
3. Too thin a reed edge would also shift more energy from the lower partials
to the upper partials of the note produced than one might desire, creating
too bright a tone, particularly when in conjunction with the narrow edge of
an embossed slot.

The purpose of chamfering is to improve the aerodynamics of the reed.  From
my post of Dec. 9th:

"During one of my spells at the factory in the late '90s, I found that
Eberhard Glunz, Hohner's materials engineer at the time, had connected the
Blasmaschine [machine to test harmonicas] to an oscilloscope and computer in
order to measure reed response time and volume.   He linked the switch that
turned on the vacuum to those of the oscilloscope and computer, which would
then begin recording the data the moment the vacuum was turned on.  The
computer would produce a graph, with the x-axis indicating duration of time
in milliseconds from activation of the reed and the y-axis indicating
amplitude in decibels.  In order to ensure accuracy, he programmed it to
produce a graph showing the average of any predetermined number of
activations of the reed.

We used this system to test the technique of reed chamfering, where the
upper edges of a reed are broken (I use a small chisel to chamfer the
edges).  I attached to the Blasmaschine a Marine Band without covers, with
all but one reed taped off, and we obtained an average of ten activations,
measuring how many milliseconds it took for the reed to attain its maximum
amplitude, which can be considered its response time.  Then I removed the
harp, chamfered the reed and immediately replaced it onto the machine for
another ten activations.  This test was repeated for a number of different
reeds.  As I had already been chamfering the reeds of my own harps for some
time and had noticed through playing them an improvement in response time, I
had expected this to be confirmed in this test, and it was.  What was
surprising, however, was that there was not only an improvement in response
time but a marked increase in average maximum amplitude; chamfered reeds
were shown not only to respond more quickly, but to play louder.

Glunz said that this improvement in response and volume could not be due to
a change in the flexibility of the reed, as so little material was actually
removed, relative to the overall mass of the reed.  The improvement, he said
must be due to a change in the aerodynamics of the reed.  It would seem that
chamfering the reed's upper edges produces a similar aerodynamic to that
from a process of manufacturing high-end accordion reeds, where the upper
surface of the reed is milled while the reed is attached to a revolving
drum, producing a radius along the length of the reed, where the reed is
thickest along its middle length and gets thinner toward its long sides."

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Message: 9
Date: Sat, 27 Dec 2008 16:45:20 -0500
From: captron100@xxxxxxx

 We would like to know how you lower the reed at it's rivet end.
 Thank you for the picture of your embossing tools.  The second one  I
suppose is more accurately a "chamfering"
tool since it apparently cuts a groove into the reed plate.  It looks like a
thick needle which has
been ground on a 45 degree angle to a point.  When using this tool, do you
use some kind of guide along the reed slot or do you
do as I do, which is to stuff a relatively thick feeler gauge under the reed
and let the reed edge act as a guide?
 Thank you for sending the picture of your chamfering tool, which was made
by grindingan old reed file, thereby turning it into a
chisel.  The original link which appeared in your mail did not work for me,
so I fooled around with it and finally got it to work.
Hopefully this will show the link in a workable form:
http://docs.google.com/View?docid=dckkn2d6_32vjf4qr  .  With this tool
I assume you run the chisel along the edge to remove metal along the reed's
edge.  Can you please tell us what this
accomplishes?

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Message: 11
Date: Sat, 27 Dec 2008 11:35:57 -0500
From: Robert Coble <robertpcoble@xxxxxxxxxxx>

I do have a question or two regarding chamfering.(1) When using the chisel
to chamfer, do you push the chisel or dragit along the reed?(2) Is the
purpose of chamfering to simply narrow the edge of the reed, to reduce the
gap between the reed edge and the reedplate slot, or to improve the
aerodynamic flow around the reed and into the slot? Or, isit some
combination of all these factors?(3) What is the reason for not taking the
chamfer all the way down tothe opposite edge?