Re: [Harp-L] Tolerances on Harmonicas and the Manufacturing process.



I agree to all that Harvey has said about tolerances and manufacturing processes. I also agree that small reed tolerances are better than large ones.

However, I raise the following questions about the importance of variations of the clearance between the reed and slot:

If the nominal clearance is .001". Reeds vary in length from .75" to .30" for an average of about .50". The width of a reed is about .08" Thus the clearance area around the average reed is (.5 + .5 + .08)" * .001" = .00108 sq in.

However, consider the gap of the opening reed in the same chamber. A typical gap for a .5" long reed is .008" The area through the gap (two triangles of .5 * .008" plus .08" * .008" at the tip) is .00464 sq in. ...almost five times the clearance area. If by means of tolerances or embossing you close or open the clearance by .0005" or 50%, you have changed the clearance area by .00054 in sq. However, you have changed the total leakage area by only .00054 / (.00108 + .00464) = 9.4%

Not only that but the opening reed (especially the long ones) open even farther when you blow or draw.

Thus the gap of the opening reed contributes the vast majority of the leakage area in an unvalved diatonic. I think that this remains true even if you quibble with my exact numbers.

Q. What then is the big deal with clearance tolerances and embossing? If they are significant, it must not be as simple as total leakage. It must be how completely the flow is shut off when the reed is passing through the slot.

Q. Could it be that we subjectively perceive differences in performance that are not there?

Q. Has anyone measured differences in clearance and then compared performance in a test using "blind" players?

Q. What have I overlooked?

Vern

----- Original Message ----- From: "Harvey Berman" <cscharp@xxxxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Tuesday, May 26, 2009 8:26 AM
Subject: [Harp-L] Tolerances on Harmonicas and the Manufacturing process.



It seems that all the conversations about Harmonica out of the box quality and consistency have to do with tolerances.


Tolerances mean that when you specify a product, or you manufacture a product you specify the allowable deviation from the standard you wish to achieve. This is a plus or minus situation, and the tighter the tolerances, the more expensive the product. When two or more components interact with each other, as in the Harmonica reed plate and harmonica reed tolerances are very important. For example, If the reed tolerance is on the plus side, and the slot tolerance is on the minus side, then you have a real tight fit, and a great harmonica. If it is the other way around, and the tolerances stack up wrong, then you have an airy, less than perfect product.

I figure that this is why harmonicas are not all the same out of the box. The average tolerances, I am guessing 80 percent, are the ones that you get out of the box which work as designed. The tight tolerance matchup, let say 10 percent are the ones that play great out of the box, and which we would probably pay more for if we could consistantly get them. The loose matchup, the other 10% are the ones that everyone is bitching about.

What is the answer? Maybe there could be 3 prices of lets say a Marine Band. Lets say $30 for the Normal Marine Band, and $40 for the tight one, and only $20 for the loose one (which is still with the original specs) Of couse, to separate these, probably adds another manufacturing step, and in turn raises the costs.

Before anyone slams me for now knowing what I am talking about, I will admit that I know nothing about the Harmonica Manufacturing Process, but I spent many years in other manufacturing environments. All the numbers I quoted are made up, and all of this is IMHO. Tolerance theory is real.

Harvey Berman
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