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




----- 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





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