Re: [Harp-L] Reed Profile - More Questions

"Vern Smith" <jevern@xxxxxxx> · Wed, 17 Jun 2009 15:14:11 -0700

----- Original Message ----- 
From: "Robert Coble" <robertpcoble@xxxxxxxxxxx>

To: "Harp-L" <harp-l@xxxxxxxxxx>

Sent: Wednesday, June 17, 2009 9:43 AM

Subject: [Harp-L] Reed Profile - More Questions

(1) Are specific reed profiles (mensurs?) milled in one 
pass? (It would appear so from The Harp Handbook.) I 
assume that means one specific reed type (with specific 
mensurs) is lathed into one strip of brass at one time

You can see a reed lathe in operation in the video tour of 
the Tombo factory.

http://www.youtube.com/watch?v=n548kAiq-zA

The lathe is seen at about 33s.

It appears that the lathe has cutters, each of which has the 
profile of one reed.  Each reed profile is cut into one 
entire strip of material.  The length of the strip is about 
the circumference of the lathe mandrel.
and then the individual reeds are stamped from that strip 
of brass.

A few seconds later, the same video shows machines stamping 
reeds out of the machined strips.
Dang! That seems like a lot of changes to lathe settings 
to produce a complete set of reeds! OR an enormous number 
(1500?!?) of lathes would have to exist in the factory.

It seems that there are an enormous number of profiled 
cutting tools and a way of quickly changing them in a small 
number of lathes.
I guess when you're creating gazillions at a time, it 
doesn't seem like that much work.

If you are in mass production of harmonicas, you need a way 
such as this of making a large number of reeds having the 
same profile.
I'd certainly opt for a CNC machine with a program that 
could be changed on the fly.

CNC is a way of controlling an existing machine tool. 
First, you need to design a machine tool that will do the 
job you want done...then make jobs repeatable and faster 
with CNC control.  Let us assume that the lathe that we see 
in the video or picture is the best machine tool for the 
job.  Then we might replace the tool that cuts the entire 
profile with a pointed tool that moves axially to cut the 
profile.  We could now replace the profiled cutters with CNC 
part programs for each reed.  Since the pointed cutter isn't 
removing as much material, we might be able to run the lathe 
faster.
The traditional lathe is "Detroit automation" where the 
details of the product come from the mechanical design of 
the machine...in this case the profiled cutters.  CNC is 
more versatile because the details of the product come from 
numbers stored in a computer.
(2) Are the weights (blobs) on the end of the lower pitched 
reeds milled as part of the mensurs milling process?
Yes.  In most cases they are the thickness of the strip 
stock and are not milled at all.
(3) Regardless of the process, is specific response (the 
flexibility of the reed, for lack of a better terminology) 
the reason for using a weight at the free end of the 
lower-pitched reed, rather than a more gradual taper 
(possibly requiring a much thinner reed)?
You can lower the pitch of a reed three ways:

1. Making it thinner/weaker where it bends near the rivet. 
This is the way we tune to a lower pitch.

2. Making it longer.  There are limits imposed by the 
dimensions of the harp and the tendency of very long reeds 
to vibrate in a twisting mode.

3. Making it heavier at the tip by adding material.  Some 
tuners add solder to the tip.
These weights are a way of lowering the pitch of the reed 
without making it too long.
(4) Is manufacturing convenience the reason for milling 
across the reed (laterally) instead of milling along the 
length of the reed (longitudinally)?
Yes.  I made a little machine to mill reeds longitudinally. 
It worked on only one reed at a time and used a cutter only 
1/16" in diameter.  It was not suited for mass production. 
However, it did produce beautifully smooth reeds!
 I assume that might be one of the reasons for earlier 
reed fatigue. Or, because of the fine-grained milling 
process used, is that no issue at all? (Yes, I know: 
EVERYTHING in industrial engineering is a tradeoff of 
various factors. I much prefer reeds with average 
longevity at a reasonable [to ME] price vice reeds with 
optimal longevity at an exorbitant price.)

Stress concentrations arise at abrupt changes in cross 
section.  Common sense tells us that smooth reeds would be 
better.  Tests to compare them would require very large 
numbers of specimens and would be expensive and time 
consuming.  We get by pretty well with the esisting methods.
(5) Given that the milling process is applied to the upper 
side of the strip of brass, I assume that the lower side 
of the brass is completely flat. Is that so?

Yes.  It must rest against the lathe mandrel to resist the 
cutting forces.
That would answer my earlier question about various 
substitutes (like razor blades) as reeds.

Razor blade steel is very hard.  It can be sheared for 
outline.  However, to change its flat profile to make it 
into a reed (or later to tune it)  requires grinding.  Steel 
has a lower density and a higher modulus of elasticity than 
copper alloys such as brass and bronze.  A steel reed would 
be thinner where it bends and thicker at the tip.  Shim 
stock from an industrial hardware source (e.g. McMaster 
Carr) is a much better source of material for the DIY 
reed-maker.
Thank you all for participating in this discussion. Lest 
anyone wonder, I am NOT a machinist nor a mechanical 
engineer (that must be painfully obvious to those of you 
who are experts in those fields); I am a retired software 
engineer - and I intend to stay as retired as I can 
afford! I'm interested in the topic of harmonica 
(including reeds) design as a means to the end of making 
my own harmonicas play better for me.

Making a responsive reed of predictable pitch and long life 
using exotic material is an interesting but daunting task. 
You not only need to be a machinist, but have machines that 
can work on tiny reed-sized pieces of metal to tolerances of 
.0002" (about 1/10 the diameter of a human hair).  Unless 
the challenge is what attracts you and not just getting the 
reeds, you are better off to buy your reeds.  It is like 
boating..... get a power boat if you are interested in the 
destination, get a sailboat only if you enjoy the process of 
getting there.
I have no intention of trying to compete with any 
commercial company. That said, I do wish Brad Harrison 
good luck in creating his business; he's going to need it 
to break into a long-established, VERY competitive and 
EXTREMELY exacting environment.

We all wish Brad well.   He can probably make harmonicas. 
Whether or not they will be perceptibly superior to those on 
the market remains to be seen. However, don't expect any 
miracles.
Vern 