[Harp-L] Embossing and Chamfering

["Rick Epping" <rickepping@xxxxxxxxx>]

A few notes on embossing and chamfering:



Embossing:


...What clearance do you aim for when you emboss?



When embossing for maximum performance I aim for a clearance of about
0.01-0.02mm along most of the length of the reed. Approaching the rivet end
however, this clearance might be reduced up to a zero clearance without
causing difficulty, at least in the higher-pitched reeds.  This is possible
because there is little reed movement near the rivet end to interfere with
the slot, particularly in the higher reeds, which are relatively thick
there.  Some accordion reed specifications have included a zero clearance
near the rivet end.



I emboss the free end of the slot much the same as the sides, but if there's
excessive initial clearance I don't emboss to the degree that the level of
the burr is more than a couple of tenths of a millimeter lower than that of
the sides.  After embossing, it's important to lower the reed at its rivet
end into the slot to compensate for the embossing having lowered the
effective edge of the reed slot.



One result of embossing is that it creates a very short moment in which the
swinging reed almost completely shuts off the airflow through the slot,
similar to the effect produced by a thin reedplate.  This amplifies the
upper partials of the note produced by the reed, producing a brighter tone -
not necessarily a desirable characteristic. An unembossed harp with decent
factory clearances, though requiring somewhat more effort to play than a
closely embossed harp, can produce a tone more suitable for some musical
applications.  I play Marine Bands with DymondWood or sealed pearwood combs
and closely embossed reeds when playing loud, hard-driving music and prefer
Special 20s with more moderately embossed reeds for softer music.


...How do you measure the clearance?



During the course of developing new reed/slot clearance specifications with
Hohner, I evaluated a number of vintage, production and test sample
reedplates, the clearances of which were measured by Hohner's CNC video
measuring microscope.  Using this machine while at the factory I was also
able to measure the clearances of reeds I embossed.



I had no such means of making absolute measurements back in my office in
Richmond but I was able to make relative comparisons of different reed/slot
clearances using a microfiche reader I salvaged when Hohner switched its
record keeping to a CD-based system.  By placing reedplates on the fiche
carrier I was able to get good silhouette images of clearances, which were
then easily photographed.



>From this work I developed a reasonable eye at estimating reed/slot
clearances, so, while I don't measure the clearances of the harps I now work
on, I know fairly well what to look for through a lens.





I have two tools I use for embossing, both of which are shown at the
following link:



http://docs.google.com/Doc?id=dckkn2d6_22m6mx4gf8





One tool is for quick and easy embossing, where both sides of the slot are
embossed at the same time but where the slot can only be embossed about 2/3
of the way back to the rivet without affecting the offset of the reed.  The
other tool is for embossing the entire slot, one side at a time.  Also shown
on the above link is a tool I use for clearing the slot if too much of a
burr is raised.  It's simply a strip of .001" feeler gauge set into an
X-acto blade handle.  The haft cut off of a blade is set into the handle to
keep the strip secure.





Chamfering:



The link below has photos of a reed before and after chamfering.  Included
are photos of the chisel I use to chamfer along with a description of how to
make and sharpen the chisel:



 *http://docs.google.com/Doc?id=dckkn2d6_32vjf4qr*<http://docs.google.com/Doc?docid=dckkn2d6_32vjf4qr&hl=en>





Best regards,

Rick