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tumbling reeds?


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HI All,

 

I'm experimenting with making reeds from stainless steel, the kind that is normally used in compressor valves. I know a few others have tried this and there have been some previous topics. The data sheet for a particular alloy I have brought has this advice:

 

"A good tumbling operation giving a round, smooth edge is necessary in order to minimize stress concentrations. Tumbling also increases the residual compressive surface stresses which gives a significant further improvement in fatigue properties."

 

In terms of concertina reeds, does anyone have any experience of tumbling the reeds post working? The increase in fatigue performance sounds welcome, if not really necessary, but I'm wondering if it has any effect on the sound, i.e. acceleration of the normal work hardening by playing = mellower initial sound. Also, rounded edges sound to me like bad news for a reed, but that depends on what sort of radius you could expect to be left with, as I doubt it will knock a lot of material off, especially if the shot  is of a softer metal.

 

What are your thoughts - is it worth the investigation?

 

Paul.

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26 minutes ago, Jake Middleton-Metcalfe said:

I would advise against tumbling, you want very precise non rounded edges on reed tongues, especially on the underneath. I would not recommend stainless either, its best to just use blue tempered spring steel, it works really well

 

Thanks Jake, I did appreciate that a sharp edge underneath was critical.

 

One thing blue tempered spring steel isn't good for is not rusting - my initial line of enquiry was trying to make a high quality instrument more resistant to a marine environment. I'm interested in why stainless is not recommended, does it have other disadvantages or is it just not as good in terms of sound quality? I'm getting what I'd describe as a very pure tone in experiments, with a very good response at low pressures, but maybe not the harmonic depth of some non-stainless reeds. However, I also have a very non-standard shoe design, and have a lot to learn on profiling, so many factors at play.

 

I will no doubt post some updates as I go.

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As with many things Ithink it's a case of learning from the "old ways", but not being afraid of trying something new. How else is progress to be made? I just just checked the net and stainless steel was only invented in 1913, so for early concertinas from the great makers it wouldn't even have been an option.

 

As for the tumbling, it depends how much rounding occurs, but if it is a gentle "Shot peening" and polishing process then I'd have thought it would produce very durable reeds, as long as you dont then scratch the root too much in the tuning.

 

More power to your elbow for trying these things out - something I'd like to tinker with once I am retired.

 

Has anyone tried laser cut stainless steel reed shoes?

 

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I'm not sure about the tumbling question, but I believe there are harmonicas with stainless steel reeds. Not sure how common they are though. It's probably worth a try if you're building a special 'marine grade' concertina.

 

I find that shearing the reed steel leaves fairly rough edges, so I shear them over-width and file the edges smooth, which I imagine removes any stress points where a crack could potentially start. Perhaps the tumbling recommendation is intended as a less labour intensive way to do the same thing.

 

At what stage would you tumble them? Right after shearing? After filing the edges to fit them to the frame? After profiling? After final tuning?

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14 hours ago, Clive Thorne said:

As with many things Ithink it's a case of learning from the "old ways", but not being afraid of trying something new. How else is progress to be made? I just just checked the net and stainless steel was only invented in 1913, so for early concertinas from the great makers it wouldn't even have been an option.

 

As for the tumbling, it depends how much rounding occurs, but if it is a gentle "Shot peening" and polishing process then I'd have thought it would produce very durable reeds, as long as you dont then scratch the root too much in the tuning.

 

More power to your elbow for trying these things out - something I'd like to tinker with once I am retired.

 

Has anyone tried laser cut stainless steel reed shoes?

 

Thanks Clive, I'm definitely for experimenting. I'm actually using 3d printed stainless steel shoes for these, which is working out very economically at the moment, around £5 per reed.

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3 hours ago, alex_holden said:

I'm not sure about the tumbling question, but I believe there are harmonicas with stainless steel reeds. Not sure how common they are though. It's probably worth a try if you're building a special 'marine grade' concertina.

 

I find that shearing the reed steel leaves fairly rough edges, so I shear them over-width and file the edges smooth, which I imagine removes any stress points where a crack could potentially start. Perhaps the tumbling recommendation is intended as a less labour intensive way to do the same thing.

 

At what stage would you tumble them? Right after shearing? After filing the edges to fit them to the frame? After profiling? After final tuning?

Hi Alex,

 

I was thinking to profile, set and tune the reed to within 20 cents say, then take it out and tumble it before resetting and fine tuning. I was imagining any operation would probably affect the tuning, so there would need to be some fine tuning afterwards. However, if I did end up with round edges I guess I could do some tumbling earlier in the process on an overwidth reed, then file back to a clean edge.

 

Are there any other things concertina makers employ to make there instruments sound more played in to begin with? For example, a device that sounded a reed at a steady (or even programmed to be varying) pressure constantly for several hours might be beneficial (as long as it was in a sound proof enclosure or far from habitation!)

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It will be interesting to see how the experiment turns out. Are you thinking of putting all 60 (or whatever) reeds into one of those small rock tumbling machines with some abrasive media for a couple of hours, then sort them into order again after you take them out?

 

I haven't tried building a reed breaking-in machine myself. There are a few practical issues to solve, not least making it soundproof enough to avoid getting an ASBO from the neighbours!

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11 minutes ago, alex_holden said:

It will be interesting to see how the experiment turns out. Are you thinking of putting all 60 (or whatever) reeds into one of those small rock tumbling machines with some abrasive media for a couple of hours, then sort them into order again after you take them out?

 

I haven't tried building a reed breaking-in machine myself. There are a few practical issues to solve, not least making it soundproof enough to avoid getting an ASBO from the neighbours!

 

Indeed! If there was a way to vibrate the reed outside of the shoe, then it would be virtually noiseless.

 

I was thinking of starting with using shot only, with some detergent perhaps, but not abrasive paste or finer grain material. Really relying on multiple impacts on the metal to promote hardness, rather than it being a poishing operation per se, which I'd do more efficiently with micromesh files. Sorting them out again afterwards sounds a nightmare, unless I can scratch a number on the spare length at the base.

 

Those tumblers seem a lot of money for what they are, I might set about making my own.

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Jake, I am not wedded to the idea that reeds need to have a precise bottom edge. I certainly round the top edge but that is a defence against burrs which don’t have to be very large at all to hit the frame. The bottom edge I take the sharpness off. What are your thoughts?
 

Some time ago I made a couple of reeds which were intended to have no sharp edges, they were akin to an ellipse shape but with a flattened bottom. The frame was also rounded over so the tightest point of clearance was .5mm from the top of the frame. So a rounded edge reed was passing through a rounded edge frame, but maintaining a tight clearance. 
 

The genesis of this experiment was me thinking of the noise a strong wind makes when it moves across a sharp edge. It is full of shrieking higher partials, much like some concertinas.  When the clearances In reeds get tighter higher partials seem to get louder. I wondered whether this was due to pressure on sharp edges. 
 

So what happened? In the tuning rig the reeds were less edgy than equivalent square edged reeds but still had power. I decided self-importantly that I had made a major development in concertina technology. I fitted the reeds to a concertina and was disappointed to find the difference could no longer be heard. My conclusion, with no real evidence, was that the body of the concertina was already filtering out the higher partials not created by my new reeds. Subsequently I discovered similar technology at use in accordions, the reeds are called “bombate” (my spelling could be wrong here) reeds. 
 

My other great contribution to concertina tech, a layout for small LHS anglo reedpans,  a month’s work, kept me happy until I discovered it was near identical to someone else’s long standing design. But I digress. 
 

So I am not against a square bottom edge on a reed, I just don’t think it is important. 
 

As for tumbling reeds; there are a lot of alloys of stainless steel, I would choose the alloy with care, (sounds like using compresser tech might have sorted this out already) create the reed blank in a way that does not leave invisible cracks (beware of curved sharp guillotine blades), dress the top corner with a diamond file, and take a pass along the bottom edge with the same. And don’t leave any acute crevasses in the profiling, cracks most readily start in a sharp internal corner. The place it is easiest to fall into this in a reed is dropping the thickness from your blank thickness, say 15thou, down to, say, 10thou, in too short a distance. Always moving the file sideways while filing helps guard against this.  

 

Stainless has other issues, it is not easy to file so hand profiling the reeds would be tricky, but only more difficult, not impossible.
 

Do steel concertina reeds work harden through playing? I have never heard anyone posit that. I think we agree time changes them, some suggest the internal stresses even out to their new shape and use. It might just be as quick to play it a little when finished. Dana has a machine which exercises all of the reeds in a pan at once (one direction at a time) to break reeds in. I think he described it as hard to listen to.  
 

If you are thinking of using stainless reed clamp screws in your stainless frames and you think you might want to take them back out you might need to use an anti-seize compound, stainless on stainless is a most unhappy combination, it galls.


 


 

 

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6 hours ago, Chris Ghent said:

Some time ago I made a couple of reeds which were intended to have no sharp edges, they were akin to an ellipse shape but with a flattened bottom. The frame was also rounded over so the tightest point of clearance was .5mm from the top of the frame. So a rounded edge reed was passing through a rounded edge frame, but maintaining a tight clearance. 

 

Thanks Chris, did you notice a reduction in efficiency or responsiveness from the rounded-edge reeds? I have the same experiment on my TODO list.

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6 hours ago, Chris Ghent said:

Jake, I am not wedded to the idea that reeds need to have a precise bottom edge. I certainly round the top edge but that is a defence against burrs which don’t have to be very large at all to hit the frame. The bottom edge I take the sharpness off. What are your thoughts?
 

 

Its a practice I picked up from an older concertina maker over here, Geoff Crabb. I believe the thinking is that when the edges are rounded underneath you are creating clearance which will not help the response of the reed, but all I was told is "square edges on underside of reed tongue is good for response". It stands to reason that rounded edges on the underside of the reed tongue would just make a wider gap for air to get through before the reed starts and make the response slower. I do de-burr the underside edges and top edges very lightly with probably 800 grit paper after they are filed to fit the frame and with square edges, but not to any degree which would cause a little 45 degree angle that wasn't microscopic. I hope this explains the reasoning well enough.

 

Edited by Jake Middleton-Metcalfe
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On 12/19/2020 at 7:45 PM, alex_holden said:

 

Thanks Chris, did you notice a reduction in efficiency or responsiveness from the rounded-edge reeds? I have the same experiment on my TODO list.

There seemed to be no difference in response; I’ll see if I can dig the reeds out, I think I saw them sometime in the last year. I could even send them over to you, might save some time for you. 
 

I think there was no difference in response because the response is affected by the clearance and this clearance was not changed, just the lead up to the “compression” point and the ramp down were less aggressive. 

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On 12/19/2020 at 7:56 PM, Jake Middleton-Metcalfe said:

 

Its a practice I picked up from an older concertina maker over here, Geoff Crabb. I believe the thinking is that when the edges are rounded underneath you are creating clearance which will not help the response of the reed, but all I was told is "square edges on underside of reed tongue is good for response". It stands to reason that rounded edges on the underside of the reed tongue would just make a wider gap for air to get through before the reed starts and make the response slower. I do de-burr the underside edges and top edges very lightly with probably 800 grit paper after they are filed to fit the frame and with square edges, but not to any degree which would cause a little 45 degree angle that wasn't microscopic. I hope this explains the reasoning well enough.

 

I know Geoff, he visited here about 15 years ago.  He loves to talk about making concertinas and it is all interesting.
 

On the experimental reeds I am not talking about creating any extra clearance or wider gap. Leaving those reeds aside and talking about every day reeds,  it sounds like you do similar things to me on the underside, on the top side I hit it a little harder, but yes, I’m talking microscopic. 

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I may as well have fun with this, but first, I'm assuming that by "rounded edge" you mean that the very thin side of the tongue is not a flat plane at right angles to the upper and lower surfaces, but rather it has a curved, convex shape . I base my comment on that picture.

I tend to agree with Chris that such a feature should not affect the sound too much. But as usual, we can devise other possibilities in special instances.

Such as the start transient and the amount of pressure needed to start vibration. Since the quiescent tongue offset is sometimes comparable to the tongue thickness, a rounded edge can conceivably require more pressure to start, simply because the bottom surface of the tongue enters the slot first, and if the edge is square (not rounded), less pressure would be needed than the pressure required to immerse the center portion. That suggests a rounded edge may require higher starting pressure. But even that's a guess because, in the case of the rounded edge, the larger air gap the bottom edge may still provide the proper conditions to start vibration.

The start of vibration itself is a dynamic issue, involving the shedding of vortices moments before the actual start. The vortex shedding causes the tongue to vibrate at first with very low amplitude, low enough so that the tip doesn't enter the slot. This is a phenomenon in architecture called vortex induced vibration of cantilevers. With tongue vibration, eventually the amplitude becomes large enough for the tip to enter the slot, at which point the common mechanism for self induced vibration takes over with a rapid buildup to steady state. The whole event may take tens to a hundred or so miliseconds, and by musical instrument standards, this is a long transient start time. In fact, it's so long that organ builders didn't want to use free reed pipes in their organs. But in recent times they have become more forgiving.

So one sees how picayune we must be in order to understand some seemingly simple things about this amazing sound source.

Concerning the sound of reeds played at normal volumes, I'd reason that a rounded edge shouldn't have much affect, simply because the tongue thickness, say 0.010 inch, is much much smaller than the amplitude of vibration of the tip portion of the tongue. Whether that 0.010 inch contains a rounded feature shouldn't make any difference. I base this guess on the fact that the harmonics in the acoustic sound are a result of the aerodynamic forces acting throughout the cycle of vibration. Thus, the whole period of motion produces these harmonics, and tongue thickness itself is a minor dimension compared to the relative amplitudes and surface areas contributing to the total motion.
But I could be wrong.

We can again get a bit picayune here and wonder about very soft sounds, when the vibration amplitudes aren't as large. But I'll not go there.

One suggestion would be to take one step at a time. Make two identical reeds, one with rounded edge and the other without, install them and play them. If you're energetic, make three sets at different pitch ranges. I think it would be foolish to make a whole reed set in order to check out such questionable advantages.

Concerning fatigue of tongue materials and simply speaking, metals have what are called "endurance limits," meaning they break after a sufficient number of times in cyclic motion. The number of maximum cycle times decreases the higher the stress experienced. If we forget about internal residual stresses and stress inducing features and defects, most steel reeds last indefinitely because the stress levels in concertina playing are low enough, except sometimes for the very longest tongues. In this regard, some here may be interested in a long discussion on endurance issues we had on this site eight years ago:
https://www.concertina.net/forums/index.php?/topic/14533-why-do-brass-tongues-break/

Regards,
Tom
www.bluesbox.biz

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24 minutes ago, ttonon said:

... The whole event may take tens to a hundred or so miliseconds, and by musical instrument standards, this is a long transient start time. In fact, it's so long that organ builders didn't want to use free reed pipes in their organs. ...

 

I'm surprised at this. The beating reeds used in organs have a much bigger air gap than a free reed, so one might expect it to take even longer to build up sufficient amplitude to start beating (the equivalent of entering the slot). With mouth-blown beating reeds (clarinet, saxophone) the lips and/or tongue can be used to hasten the process, but not in a pipe organ.

 

One reason why organ builders might prefer beating reeds to free reeds is ease of tuning. A little wire slider runs up and down the beating reed to tune it and this can be adjusted without removing or dismantling the pipe. (I know - I did it decades ago when I was an apprentice organ builder!)

Edited by Little John
To add information about tuning.
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9 hours ago, Chris Ghent said:

I know Geoff, he visited here about 15 years ago.  He loves to talk about making concertinas and it is all interesting.

wider gap. Leaving those reeds aside and talking about every day reeds,  it sounds like you do similar things to me on the underside, on the top side I hit it a little harder, but yes, I’m talking microscopic. 

 

I think I might have misunderstood what you were originally saying about the experimental reeds, sorry.

 

 

Ah Geoff is great, I sometimes have a new idea or want to try something different but encounter a problem or obstacle and he would say something like "well actually we tried that in the 60s and xyz was the best way.." 

 

 

 

 

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