[Harp-L] Re: Vibratory Stress Relief

[Rick Epping <rickepping@xxxxxxxxx>]

Sorry, I forgot to edit the Subject header on this message...

> Hi Vern, Hi Joel,
> 
> No visible change to the reeds occur through using the type of domestic ultrasonic cleaner sold for jewelry, etc. - neither in their shape nor in their offset.  Normally, if a reed's curvature or offset is significantly altered it will result in a lowering of pitch rather than a raising of pitch.  And in the couple of years I've been using one of these cleaners I've not noticed any decrease in the reeds' performance or durability.
> 
> As Vern pointed out, VSR is not considered effective for the relief of stresses in heavy cold-rolled metals, nor for many alloys, both of which harmonica reeds are.  Might this indicate that an ultrasonic bath would not affect the necessary spring tension of the reeds introduced through cold-rolling, but only the tension added later in working the reeds by hand? 
> 
> Furthermore, industrial VSR machines operate at low frequencies, generally in a frequency band of 0 - 100 Hz <http://www.stressreliefengr.com/stressreliefintroduction.html>, sweeping through this range to identify, match and eliminate the problematic peaks in the resonant frequencies of the workpiece.  Domestic ultrasonic cleaners generally operate at between 30,000 - 40,000 Hz, well above the resonant frequencies of any harmonica reed, so the comparison of an ultrasonic bath's effect with that of an industrial VSR machine is perhaps limited.
> 
> Best regards,
> Rick
>> 
>> ------------------------------
>> 
>> Message: 6
>> Date: Tue, 04 Nov 2014 09:00:10 -0800
>> From: Joel Fritz <williemctell@xxxxxxxxx>
>> Subject: Re: [Harp-L] Re: Vibratory Stress Relief
>> Cc: "harp-l@xxxxxxxxxx" <harp-l@xxxxxxxxxx>
>> Message-ID: <5459061A.5000606@xxxxxxxxx>
>> Content-Type: text/plain; charset=UTF-8; format=flowed
>> 
>> Good points on stress relief.   Having done a lot of thermal stress
>> relief in a previous life as a heat treater, I can testify to what
>> happens.  I think that stress relief of reeds is probably a bad idea
>> since the work hardening from manufacturing is what makes the reeds
>> springy.  Controlling the amount of stress relief is tricky.  It's not
>> like tempering heat treated steel.  Admittedly grinding and gapping will
>> probably add some internal stress.
>> 
>> On 11/4/2014 8:38 AM, Vern wrote:
>> > De-stressing a piece of sheet metal (a reed) usually results in a change of shape.  If you bead-blast a strip of cold-rolled metal, it curls up like a potato chip.  If any significant amount of stress relief occurs in the ultrasonic bath, I would expect the gap to changeâÃÂby different amounts in different reeds.  Have you checked the gap size before and after? Could the pitch change arise from gap change?
>> >
>> > It seems intuitive that relaxing stress would lower the modulus of elasticity lowering the pitch.   However, I havenâÃÃt researched this.
>> >
>> > I donâÃÃt think that it is clear that the change in stress changes the modulus of elasticity.  Elasticity is under the radical in the pitch equation so that a change of 2% in elasticity would produce only a 1% change in pitch.
>> >
>> > Work-hardened brass would not seem to be a good candidate for VSR according to the following statement by Bonal, maker of VSR equipment:
>> >
>> > "5) What are the limitations of Meta-Lax stress relief for metals?
>> > Meta-Lax stress relief is not effective on metals where mechanically induced stresses are dominant (for example cold rolled steel plates) where machine stability is the goal.  Copper and high copper content metals do not respond consistently. âÃÃ
>> >
>> > The stresses in reeds are mechanically induced by machining (as opposed to unequal rates of cooling) and the copper content is high.
>> >
>> > Vern
>> >
>> >