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Rod Pearce

Tuning stability

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How long would you expect a recently tuned instrument to stay in tune for?

 

I have tried to find some information by searching the forums but the number of hits from searching 'Tuning' is enormous. So I have opened a new thread on this subject.

 

I have tuned a number of instruments over the last 12 months, all reeds to within 1.5 cents after several passes. However, I have noticed that when checking the instruments after a few weeks / months a number of reeds have gone out of tune, or just not sounding correctly.

 

Is this to be expected ie an instrument'ss tuning should be expected to change periodically? If this were the case surely the majority of instruments in day to day use would be out of tune.

Is it that the reeds are getting past it and are no longer able to retain their tuning for long periods?

 

Any thoughts would be appreciated

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Colin Dipper tuned my Wheatstone Model 24 in 1994. It has been played a lot since then and its tuning is still excellent. I recently looked at the set of a few reeds which needed a bit more pressure than others to start sounding and that is much better now.

 

I think it’s probably not the reeds: more likely to be valves or reed shoes being a bit loose. Perhaps modern homes with low humidity are to blame.

 

Others who have more experience of maintenance and tuning may have different opinions.

 

Steve

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Steve

 

Thanks for your feedback. Much appreciated.

 

As the concertinas in question have undergone a full refit of valves and pads, I would not expect the valves to be the problem. I am encouraged that your Wheatstone has remained stable, there is hope for me yet.

 

When tuning I did notice that a number of the reeds appeared to be quite thin as if they had been tuned a number of times previously. I will be fine tuning these instruments again soon so time will tell.

 

Regards

Rod

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Rod, I’m under the impression that the tuning of normally played steel tongues in concertinas would last an indefinite amount of playing, and I agree with Lofty that any changes are most likely due to changes in other materials than help define the pitch. 

 

I can substantiate my view with some technical data.  Some metals have a property called endurance limit, which means that, when subjected to periodic stress that completely reverses, as in the case of a vibrating reed tongue, and provided that the maximum stress experienced is limited to a certain level, the material can withstand an infinite number of cycles.  Of course no one has verified an unlimited number of cycles, so suffice it to say that the number of cycles is extremely high, even more than 100 million or so. 

 

Other materials do not have this property, and there is no maximum stress level for infinite endurance.  For these materials, as the periodically applied stress is applied, the number of cycles will always increase as the applied stress is lowered, but there's no lowest stress level that will allow the “infinite” number of cycles.  Such a state of affairs is represented on a “SN” or Stress-Number graph, available so easy now on the WWW.  Materials with an endurance limit have a curve that becomes horizontal at some lower level of periodically applied stress, while others have a curve that always drops as the number of stress reversals increases. 

 

Spring steel has an endurance limit, and thus, if the amplitudes of vibration of steel reed tongues remains below a certain maximum, they will theoretically never break, which probably means they will never undergo fatigue effects, always remaining perfectly elastic.  I do admit that my addition of this last “probably” phrase is my own guess, though it’s an educated guess that I believe many makers would support.  I remember Richard Morse making such a statement in this Forum.  The allowable stress limit for spring steel (AISI 1095) is about 43% of its ultimate yield strength, providing I believe a very convenient window for tongue design. 

 

In contrast, brass does not have an endurance limit, and we know brass reed tongues tend to break.  But there’s more to this story.  Several of us members have already discussed many of these issues here in a thread published in 2012,   I uploaded a supporting document for some of the relevant points I made in that thread, and for your convenience, I attach it here, which is a doc file showing two graphs.   The first graph is more relevant and I need to explain that the “endurance limit for brass” line in that graph is a stress level that would permit a very large number of cycles, and I don’t remember off hand what that number is, but at least 10^7.  Importantly, except for the longest reeds, steel tongues mostly have stresses under the maximum for infinite endurance, but many brass reeds experience stress levels above that (chosen) endurance limit. 

Best regards,

Tom

www.bluesbox.biz

Steel and Brass Stress.doc

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Tom

 

Thanks for your very thorough and enlightening explanation. It will take me some time to assimilate it! I am unable to open the attachment, though.

 

I am taking from this and Lofty's reply that the reeds are probrbly OK and I should look at other factors.

 

Incidentally. I came across this thread after I posted my initial question. More food for thought.

 

Rod

 

 

 

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