Re: [Harp-L] Re: Vibratory Stress Relief

[Vern <jevern@xxxxxxx>]

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 changeâby 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 havenât researched this.

I donât 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. â

The stresses in reeds are mechanically induced by machining (as opposed to unequal rates of cooling) and the copper content is high.

Vern

> On Nov 4, 2014, at 3:45 AM, Rick Epping <rickepping@xxxxxxxxx> wrote:
> 
> Hi Mike,
> 
> I regularly clean most of my harps in the ultrasonic because they're either
> partially or fully valved and the valves need to stay clean to prevent
> sticking and popping.  So this morning, after noting the pitch of the eight
> reeds in holes 4-7, I cleaned in the ultrasonic one of my unvalved harps
> that hadn't been cleaned in a while and had a bit of sediment on the
> reeds.  The results after noting the tuning a second time, post-cleaning,
> are as follows:
> 3 reeds went down in pitch
> 3 reeds went up in pitch
> 2 reeds had no change
> Average change: 0 cents
> Maximum change: up 3 cents (one reed)
> 
> I use new replacement reeds, so there should be little, if any sediment on
> them.  As for bits of metal left on the reeds from scraping or filing (I
> use scrapers, files and, for chamfering, a chisel), on average most of the
> metal removal occurs along the entire length of the reeds' long edges from
> the chamfering.  The "pitch-neutral" point on a reed - that is, the point
> along the length of the reed at which neither the removal nor addition of
> material will alter the reed's pitch - is, for most reeds, about one third
> the distance from the tip to the rivet pad.  So the area toward the back of
> the reed where removal of material will result in a lowering of pitch is
> about twice that of the area near the tip where material removal will
> result in a raising of pitch.  This even includes those low reeds where the
> unmilled weight at the tip can extend to half the reed's length or more.  I
> would think that any significant deposits scattered evenly along the reed,
> when removed by the ultrasonic, should result in a lowering rather than a
> raising of pitch.
> 
> Best regards,
> Rick
> 
>> 
>> ------------------------------
>> 
>> Message: 10
>> Date: Mon, 3 Nov 2014 15:23:26 -0500
>> From: Michael Easton <diachrome@xxxxxxxxxxx>
>> Subject: [Harp-L] Re: Vibratory Stress Relief
>> To: Harpl list <harp-l@xxxxxxxxxx>
>> Message-ID: <B7A09B68-7DDF-4AF6-9CC3-D7BDC309343E@xxxxxxxxxxx>
>> Content-Type: text/plain;       charset=windows-1252
>> 
>> Hi Rick,
>> Since I get the digest I donât know if any replies came in yet after your
>> posting.
>> 
>> Have you tried checking the other reeds before placing the plates in the
>> ultrasonic?
>> 
>> Iâm guessing the change in pitch might not be the reed relaxing but the
>> scraped reed material flaking off the reed that is contributing a bit to the
>> raise in pitch.  Yes, it could be helping with speeding up the relaxation
>> but Iâm just saying there might be a bit more to it to contribute to the
>> change in pitch.
>> 
>> Iâve used files, very sharp dental burs and Shofu Brownies in rotary tools
>> and found the Brownies required the least amount of adjusting since the
>> reed was being
>> polished, followed by the dental burs then files and scrapers requiring
>> the most adjustments after replacing a reed.
>> 
>> I think in general if you can place a set of plates in an ultrasonic
>> before checking the tuning you can get a more accurate reading due to the
>> lack of saliva and oxide buildup
>> hanging around on the reeds and to some degree the windsavers on models
>> having them.
>> 
>> Mike
>> www.harmonicarepair.com
>> 
>> 
>> 
>> 
>> On Nov 3, 2014, at 10:46 AM, harp-l-request@xxxxxxxxxx wrote:
>> 
>>> 
>>> Message: 11
>>> Date: Mon, 3 Nov 2014 15:37:58 +0000
>>> From: Rick Epping <rickepping@xxxxxxxxx>
>>> Subject: [Harp-L] Vibratory Stress Relief (VSR) for reeds
>>> To: "harp-l@xxxxxxxxxx" <harp-l@xxxxxxxxxx>
>>> Message-ID:
>>>      <
>> CAJFTUGwuePAe6FTPu0YFAkALaSq2dhusPDf1n8OxzFAmEJNB2Q@xxxxxxxxxxxxxx>
>>> Content-Type: text/plain; charset=UTF-8
>>> 
>>> Hi folks,
>>> 
>>> This message is about one possible benefit of using an ultrasonic cleaner
>>> on newly replaced reeds.
>>> 
>>> The work that reeds are subjected to through such procedures
>>> as profiling, riveting, centering, chamfering, curvature adjustment and
>>> gapping, adds stress to the reeds.  As the tuning of a reed can be
>> affected
>>> as a reed de-stresses, the Hohner factory gives newly assembled
>> reedplates
>>> a rest period to de-stress before tuning.  Alternatively, Asian harmonica
>>> factories heat treat reedplates to de-stress them.
>>> 
>>> In my experience, new replacement reeds that I have riveted onto a
>>> reedplate tend to go up in pitch over the course of a week or so, and
>>> require an additional tuning once they become stable.  Lately, however,
>>> I've been using an ultrasonic cleaner in an attempt to VSR treat plates
>>> with newly replaced reeds, and find that after using the cleaner's
>> maximum
>>> time setting of 8 minutes, new reeds increase in pitch by as much as 8
>> or 9
>>> cents.
>>> 
>>> I've only been paying attention to this effect for the last half dozen or
>>> so reeds I've replaced and have not as yet experimented with employing
>>> longer periods of VSR, but it looks like it might be a useful treatment
>> for
>>> quickly stabilizing a reed's tuning, if not also for delaying the onset
>> of
>>> reed failure by elimination of residual stress before a new reed is
>>> subjected to playing.
>>> 
>>> More on the subject of VSR here:
>>> http://en.wikipedia.org/wiki/Vibratory_stress_relief
>>> 
>>> Best regards,
>> 
>> 
>> 
>> End of Harp-L Digest, Vol 135, Issue 8
>> **************************************
>>