Profiling

[Terry McGee]

On to reed thickness, and, firstly, the general overview:

 

 

Treble reeds on the bottom right, bass reeds upper left. Heels at the back, tips at the front. Note, I've duplicated the heel measurement to illustrate the stock thickness under the clamp.

• We can see that most of the reeds are made from thinner stock, around 0.48mm, with the lower bass reeds cut from 0.82mm stock.
• All reeds are thinned, compared to the starting stock. It is perhaps surprising that a thinner stock isn't used as the starting point for treble reeds to save the need for profiling. Perhaps one of our makers could explain why?
• Treble reeds are thinned most of the way, and are thinner at their tips than anywhere else, sharpening their pitch.
• Midrange reeds use tip mass to slow them down, lowering the pitch.
• Bass reeds make use of their thicker stock primarily by using it for increased tip mass.

 

There's probably more we could deduce from this graph, but it might be more easily seen on one of our alternative thickness graphs.

 

Terry

Edited June 5, 2014 by Terry McGee

[Chris Ghent]

Terry,

good graphs, for some reason having the widest part of the reed at the top of the graph throws me a little but the information fits with my experience, except;

[*]All reeds are thinned, compared to the starting stock. It is perhaps surprising that a thinner stock isn't used as the starting point for treble reeds to save the need for profiling. Perhaps one of our makers could explain why?

 

To digress a little, if I was describing this information I would not call it "concertina reed information", I would call it information about the reeds in this particular concertina. If you use the words "reeds in Lachenal concertinas" you are talking about potentially three generations of reed makers; in that time they can discover and lose the same wisdom a few times over. Consequently the reed stock in Lachenal concertinas could vary wildly over time; maybe for just this concertina, or perhaps just that week, or that month etc, they used only 20thou and 35thou.

 

It is my experience over a number of measures that some instruments will have 3 or even 4 thicknesses, others will only have a couple. If you are happy to weight a number of the bass reeds then the concertina can be easily made with say, 20thou and 15thou.

 

It is common to find a concertina with high reeds made from approx. 10thou stock.

 

If you had access to a range of thicknesses why might Lachenal only use two?

 

The buyer forgot to order other thicknesses and there was a gap before more was obtained?

That particular reedmaker had a thing about using only a couple of thicknesses?

The dieset used to punch the thinnest stock was blunt and the toolmaker was in Wales because his father had died and there was no-one to sharpen it? (You cannot easily use one designed for thicker stock, the clearance between male and female relates to the thickness of the stock).

The dieset had broken and there were not enough orders to be sure there was enough money to have a new one made?

Fashion.?

The reed maker had picked up his kitset of reeds, frames, clamps, screws and failed to see the stores wallah had picked some of the reed stock from the wrong bin?

Fred on the bench next door dared him to do it?

Fred, (that same bastard) bet him he couldn't do it and not have the foreman notice..?

Edited June 5, 2014 by Chris Ghent

[Terry McGee]

It is my experience over a number of measures that some instruments will have 3 or even 4 thicknesses, others will only have a couple. If you are happy to weight a number of the bass reeds then the concertina can be easily made with say, 20thou and 15thou.

 

Yes, that's a point of interest. It does seem a bit weird to make a bass reed from 0.82mm stock when you then grind most of it down to about 0.3mm, leaving only the tip region near the original thickness. I know the tips of bass harmonium reeds are artificially weighted with soft solder - does that produce a demonstrably inferior result?

 

It is common to find a concertina with high reeds made from approx. 10thou stock.

 

OK, thanks, that answers a question I had. (10thou is about 0.25mm for the benefit of the younger reader. It's about what the 0.48mm stock is ground down to in the concertina under investigation.)

 

I'd wondered if it might be important that the clamped section was considerably thicker than the mid-region, and that the transition between the two had to be gradual, perhaps to avoid a too-well-defined hinge point which might prove to be a point of mechanical weakness?

 

Any thoughts on those two questions anyone?

 

Terry

[Terry McGee]

The 3D Overview is fun, but it's hard to appreciate all it's trying to tell us. So let's look at the simpler 2D version...

 

 

Some observations:

• the navy trace is the heel, the section of reed under the clamp. Confirms just two thicknesses of stock used in this instrument.
• the G#4 reed is missing, hence the hole in the data at that point.
• you'll see I've provided trend lines for the other data (thin lines) to alert us to where the maker was forced or happened to deviate from the trend.
• the middle of the reeds and the quarter-point nearer the heel (green and yellow respectively) vary least across the range. The variation is from about +50% in the bass to around -30% in the treble, a total of 80%. That's small when we consider the frequency range is about 700%.
• the roots of the reeds also vary to about the same extent (the orange trend line is parallel to the green and yellow), but are all slightly thicker, as they transition up towards the heels.
• the middle, quarter and, to a slightly lesser extent, the root form the belly of the reed - the section over which it bends.
• the big determinant in this system is the tip of the reeds, in aqua. It varies from bass to treble over a 10:1 ratio, or 1000% - more than the ratio of frequencies. So the tips of the reeds are doing most of the heavy lifting. They are at full thickness in the bass, where their weight is needed to pull the reeds down to pitch (remember that the reeds didn't vary in length to the full extent science would have liked). And they are ground right down to next-to-nothing in the treble, where the reeds have been made longer than ideal, in order to meet other practical requirements.
• The three-quarter point (in brown) also comes into play, but not to such a degree - around 500% to be precise. So not only is it transitional between middle and tip, it also changes role as we go up the scale. In the bass reeds, it joins the tip as being part of the weighting system. In the treble reeds, it becomes part of the bending system.
• When we compare the thick aqua data trace with its thin trend line, we spot an area of divergence which will repay closer attention. We can see that the reeds from F3 to A3 would probably have preferred to be made from the thicker stock (or stock of an intermediate thickness). When you interpose a compromise in a musical system, you have to compensate somewhere else. We might have thought the logical place to compromise for lack of tip thickness would have been at the three-quarter point, but the brown trace remains on trend in that area. But check out the orange root trace - it dips dramatically to save the day. The reed-tuner, finding that the reeds are too sharp has flattened them by filing down the root more. Can't increase weight? Increase flexibility. (Heh heh, I might have been tempted to reach for the soldering iron...)

That's probably enough rabbiting on by me. By now, you'll be becoming aware of the dangers to mental health posed by too great an interest in forensic organology....

 

Terry

Edited June 6, 2014 by Terry McGee

[Chris Ghent]

Yes, that's a point of interest. It does seem a bit weird to make a bass reed from 0.82mm stock when you then grind most of it down to about 0.3mm, leaving only the tip region near the original thickness. I know the tips of bass harmonium reeds are artificially weighted with soft solder - does that produce a demonstrably inferior result?

Not in the right place and hands. I find it is good to choose the thicknes of the thinnest part of the reed and form some idea how long you would like that thin section to be and then tailor the weight of (or on) the end to balance that into tune. The wider the thin part of the reed the more gentle the curve. The thinner and longer the thin part the quicker it will start but it will become pitch unstable and lose volume.

 

Having said that...

I'd wondered if it might be important that the clamped section was considerably thicker than the mid-region, and that the transition between the two had to be gradual, perhaps to avoid a too-well-defined hinge point which might prove to be a point of mechanical weakness?

When you use stock for a low reed which is considerably thicker than the thin section it will soon come down to size a few millimetres from the root but you are in effect shortening the reed by adding a bar to the root.

However I think it would be a mistake to use a stock of the same thickness as the thin part as this would concentrate the stress at the clamp. I don't fret about using 20thou, yes .5mm, for a low reed because you are going to have at least a 9thou, yes, almost .25mm, descent to the thin part and that is enough to blend the stress point.

 

A word as to measuring systems. I think in millimetres for anything in normal life (ie non concertina related). With reeds I think in mms in anything to do with larger measurements, ie. the length of reeds. In thickness of reeds and reed clarances I think in thou because it is much easier to visualise a reed thickness moving from 21,21,20,18,16,14,11,10,10,10,10,10,10,10,12, 14, lead weight, than it is to say .525,.525,.5,.45,.4,.35,.375,.25,.25,.25 etc. I wouldn't mind betting almost everyone reading this, all three of you, can "see" the shape of the reed expressed in thou and struggle with the one expressed in mms. They are roughly the same by the way only I becaqme bored with writing the metrics and quit before the end. Only having one micrometer which is in thou probably encouraged me in this approach. Back when these things were being made in larger factories the material would have been ordered in gauge numbers, ie. 25 gauge steel plate is around 20 thou. I doubt reed makers had any access to micrometers, there probably was not one in whole factory. I say this because a person who worked for Norton Motorcycles in the 60s told me there was only one set of fine measuring tools in that factory and the toolmaker would not let it out of his sight. I can think of one concertina maker today who makes a most professional job and does not a have a vernier calliper or micrometer.

Edited June 6, 2014 by Chris Ghent

[Terry McGee]

I brought the 3D graph to the attention of my musical acoustic gurus, Prof Neville Fletcher, Research School of Physics and Engineering, ANU, Canberra and Prof Joe Wolfe, Physics UNSW. Neville responded:

 

Those measurements on the concertina reeds are most interesting, and the thickened tips make good sense. I did some theoretical work on reeds some years ago and, along with Alex Tarnopolsky, some experimental work too. You might be interested to look at this. The theoretical work is not directed just at "free" reeds but covers all classes, while the experiments involved reeds driven from a reservoir and free on the outlet, which is probably a good model for harmonica reeds. You can find these two papers for free download on the web site

www.phys.unsw.edu.au/music/people/fletcherpublications.html

with the theoretical paper being D35 on the list and the experimental paper D46. The theory can be related to "free" reeds by choosing X2=0 and X1<0, corresponding to a cavity upstream, or X1>0 for a thin upstream tube. There are two classes of free reeds discussed in the theory, described by the symbols

(sigma-1, sigma-2), so that a "blown open" reed is (+,-) and a "blown closed" reed is (-,+) in the key equations (19) and (20) that describe the performance. The numerical values of the sigma symbols are either +1 or -1.

 

You might not have stumbled over the D35 paper as its title, Autonomous vibration of simple pressure-controlled valves in gas flows, doesn't scream "concertina reeds"! It's broadly based and very mathematical, but may interest some.

 

Joe responded with an e-introduction to Jim Cottingham, Professor Emeritus of Physics at Coe College in Cedar Rapids:

Jim is very interesting in free reeds, mainly Asian ones, and has published quite a bit about them
http://www.public.coe.edu/~jcotting/
especially reeds that (unlike a concertina) are loaded by a resonator and thus not in complete liberty.
He probably knows the rest of the literature well.

A quick check of that site shows a number of interesting-looking papers, more focussed on free reeds and accessible to those without university maths.

 

Terry

[Terry McGee]

I wouldn't mind betting almost everyone reading this, all three of you....

 

"All three of you"? Gulp. You mean..... we're not alone?

 

Terry

[Terry McGee]

There's always another way to look at things, of course, and reeds are no exception. If we look down the other axis in our 3D Overview, we get an impression of how each reed is profiled. Of course, with so many reeds, that can get a bit busy, but even so, we can make out a few interesting points:

 

 

It's easy to see that we have two stock thicknesses, plunging downward then into the bellied region, and then radiating out from the middles to the tips either upwards, if we're looking at a bass reed, downward for a treble reed, or somewhere in between for the midrange reeds. Perhaps, I'd hope to see a more even spread in the radiation? We do have to remember that this work is being carried out by human beings, not robots. And probably outworkers with less than remarkable facilities at that. And we've already discussed that the decision to use only two stock thicknesses means that some fudging is going to be needed in the bellies department.

 

We do see a few reeds which look a little suspicious - eg the two shades of blue at the top of the root column. They appear to reach their minimum thickness over at middle, while most of the reeds have bottomed out by the first quarter. I suspect they are the two Eb3 reeds - if you look back at the other 2D view, you'll see there are some shenanigans going on there at Eb3.

 

Terry

[Terry McGee]

And now, one final graph. At least for now, he warned....

 

I had misrepresented the situation earlier, when I said that all the reed shoes were of the same thickness. Turned out that David had merely approximated the thickness, as he had found it seemed to be all over the shop. Turning on my best charm, I somehow convinced him to measure them anyway, which he did, in three places each. The results are below, and I have to agree with him - it's very hard to see any pattern emerging. David's feeling is: "seems to be a product of uneven rolling, uneven pressing and varied sheets of metal stamped".

 

 

Probably good to keep in mind that the nominal thickness is probably 2.08mm, 14 gauge.

 

Again, my thanks to David Hornett for taking all these measurements!

 

Terry

Edited June 6, 2014 by Terry McGee

[David Hornett]

Terry, thank you from the third person reading this. If it had not been for your pestering, and rather cunning insights when I stuffed up a few measurements, I would have given up goodness knows how far back. I have printed out your two profiling graphs and have them pinned to my tuning table.

 

BUT not a soul, ie the other two readers, assuming Danna has given up on our madness, have discussed harmonica reeds which are not profiled ... just weighted, and all the same thickness and width!! (When I break a chromatic harmonica reed every now and again, I take one from a too far gone machine, measure the length, cut the end off and it will fit in any slot beautifully, a pass with the file and it is impossible to notice the difference). Excluding the harmonicas width and common thickness, my bandoneon reeds, and of course accordion reeds have no profiling and they sound grand (some may disagree re accordions so sounding I suppose) All accordions seem to rely on is different thickness, unprofiled steel, with a dob of lead on the end when things get desperate.

 

 

And to think all this started with my request to be directed to an article on profiling.

 

Thank you again Terry, Chris and Danna

 

David

[Chris Ghent]

I know little of harmonium reeds and I have not seen bandoneon reeds, but you are wrong about accordion reeds having no profiling. If you refer back to post #71 from Terry you will see the orange line for theoretical length, this is how long your accordion reeds would need to be if they were not profiled. Profiling is, as much as anything, a way to scale the lengths of reeds such that they can fit into the same instrument. High ones can be longer and thinner so they will need less air, low reeds can be shorter so as to make the instrument portable. I would be surprised to find any western free reed instrument did not have profiled reeds.

[Terry McGee]

So, there's "clearly visible" profiling, and "less visible" profiling. I had a harmonium many years ago, but still remember the bass reeds - they were some inches long and swelled to a big lump of solder on their tips. So Patently Visible profiling.

[Terry McGee]

Oh, and one more area I'd forgotten to mention, as there is no graph associated. (Hurrah, I can hear you all cry). I pressed David to look for signs of undercutting of the reed shoe, but his advice was:

 

The angled sides have obviously been filed so they fit into the holding slots of the mounting (sound) board. Obvious parallel scratches running slightly off vertical as though filed or moved across a wheel in a jig.

Absolutely no noticeable filing internally, using a good magnifying glass. BUT the underside breakaway point (the slot's side) is rounded by a file, can still see the marks, as in the manner one would pass a file across a cut edge at an angle to clean odd burrs, the underside tip is rounded in the same manner. In fact the entire base of every reed has a small rounding across the base. I suggest that when driving the billet out with the punch, the machine would, by force of the die moving through the stamping, round the shoe up at the outer edges, as the die completed its plunge and the machine came to a stop, maybe the residual force was made to contact the shoe and force the metal back down again, almost flat, this would press inwards toward the slot, possibly crimping slightly against the die as it was withdrawn, Hence the edge which now protruded slightly into the slot would be hit with one pass of the file to remove the burr. The top of the shoe having the press stop on it and being forced back down would not spread inward so would need no touching up. Just a thought. When I fly punch things (its a little fly punch so small washers and the such like are the product) this is what tends to happen.

Heel and toe seem the same as the sides, touched up slightly.

So, would that be uncommon in having no undercutting, or is undercutting only used on some types, makes or models of concertina?

Terry

[Chris Ghent]

If you are referring to that sloping side of the reed window usually called "the relief", it is perhaps a defining feature of concertina reeds when compared to accordion reeds. Around 7° usually, varying it according to pitch is common. Traditionally formed by using a broach to square the window, the broach having a swelling at the end of its travel to create the relief. Some processes use this movement to create the outside frame bevel as well, by "flowing" the brass sideways from the window to the bevel. This leaves the rounded corners seen on the outside and inside lower corners.

 

I have seen concertina reeds with very little relief, but none without any. There are reeds sold as concertina reeds by CZ Harmonikas with brass frames similar to concertina reeds. These had vertical reed windows and riveted spade shaped reeds in the style of accordion reeds and might be better described as such.

[David Hornett]

After your above comment Chris, I have just taken a few accordions to bits (Bugari, Castagnari and a Hyde) to check this out. Yes, you are absolutely right, with the caveat that the nature of the profiling on an accordian seems much more the heavy weighing of the tips, there is little gradual build up to thickness as on the concertinas. Accordion = after a more gradual slope at the heel than a concertina has (the one I measured) a nearly flat reed from the heel then a rapidly lumpy end, the only profiling akin to concertina (the more gradual thickening toward the tip) occurs on the very bass reeds (length 49mm) on the bass side where the profiling is more evidently smoothly bellied heel to tip as with a concertina.

 

The same occurs on the deep harmonica reeds. ie, The reed is machined flat from the heel, then there is a vertical lump of metal left, and if that is not enough, a bit of silver solder is plonked on the end, hence I can just cut a long bas reed into a small reed by disregarding its end.

 

Thanks Chris, I've learnt something today.

[David Hornett]

So there are no file marks except to clean up the edge? That makes absolute sense with the internal finish I observed, much better than my theory of fly press compression.

 

David

[alex_holden]

"All three of you"? Gulp. You mean..... we're not alone?

Though I don't have much to contribute, I am following the thread with interest.

[Terry McGee]

Hmmm, 7º, eh? That's not much, is it. Given a shoe around 2.1mm thick, that puts the relief on each face at 0.25mm or 10 thou. That should make the bottom of the slot 0.5mm wider than the top. Assuming no relief under the clamped end, it would make the bottom of the slot 0.25mm longer that the top. Can you detect that in your reeds, David?

 

Terry

Edited June 7, 2014 by Terry McGee