Re: [Harp-L] Fatigue and reed life

[David Payne <dave@xxxxxxxxxxxxxxxxxxxxxx>]

Those tuning scratches were the reason I quit playing new Hohners several years ago. The MS harps were just absolutely horrible. Looked like somebody had tuned it with a pocket knife... or at least a robot had tuned it with a pocket knife, however those things are tuned. then the things weren't even in tune. I bought my last MS around 2004 or so... seems like they all looked like that to me. I don't think you beat a handmade harmonica in anything but theory.

Dave
___________________
Dave Payne Sr. 
Elk River Harmonicas
www.elkriverharmonicas.com 

----- Original Message ----
From: gary <garybond@xxxxxxx>
Cc: Harp-L List <harp-l@xxxxxxxxxx>
Sent: Thursday, April 17, 2008 3:36:57 PM
Subject: Re: [Harp-L] Fatigue and reed life

I work in the lumber industry as a saw filer. We run band saws that are 
highly susceptible to cracks. When ever  I see a deep scratch running 
out through a gullet on a bandsaw we see a potential crack. Running 
bandsaws over a wheel and moving harmonica reeds face the same stresses. 
I remember buying a Hohner MS harp and having a reed die in it almost 
right away. When I opened it up I saw a deep tunning scratch running out 
to the edge I was pretty hot under the collar. Tuning like that is 
totally unacceptable and it should have been considered a manufacturers 
defect.

Aongus MacCana wrote:
> As I remember from second year engineering school, susceptibility of a
> material to fatigue failure  could be predicted by a "notch sensitivity"
> test. A test where an ingot of the material to be tested has a standard
> notch machined out of it and is given a whack by a standard pendulum to see
> what it takes to break it off at the notch.
> A fatigue crack is most likely to start at a surface imperfection or a
> sudden change in section of a component e.g. injudicious scraping with the
> tuning file or chisel (especially across the reed!)or at the junction of the
> base of the reed where it's section is reduced after the rivetting flange.
> This suggests that 'tuning passes' would be best made along the reed rather
> than across it and a rotary grinding tool might give less surface
> discontinuity than the regular file or scraper does.
> Hot rodders have a fetish for highly polishing highly stressed components
> like engine conrods to try and ensure that there are no surface
> imperfections or stress raisers to breed fatigue cracks. They also compress
> the outer surface of such components by shot peening them (bombarding them
> with steel shot)but this does not look like a feasible strategy for
> harmonica reeds.
> Aongus Mac Cana
>
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