28 replies to this topic

[malcolmbebb]

Is everyone here even talking about the same thing?

• There's "taper" from the base of the reed to its tip, i.e., being normally wider at the base (where it's fastened) than at the tip (the freely swinging end).
• And there's the "bevel" or "undercut", in which the slot of the reed frame is wider at its "under" side than at the "top".

I'm a bit confused, but I think you two are talking about the second, while aybee and some others are talking about the first.

LOL I was thinking about the second - but thought both were included!

[aybee]

Is everyone here even talking about the same thing?

• There's "taper" from the base of the reed to its tip, i.e., being normally wider at the base (where it's fastened) than at the tip (the freely swinging end).
• And there's the "bevel" or "undercut", in which the slot of the reed frame is wider at its "under" side than at the "top".

I'm a bit confused, but I think you two are talking about the second, while aybee and some others are talking about the first.

LOL I was thinking about the second - but thought both were included!

Me too!

Chris, I apologise for jumping into this without realising the sort of dimensions involved; I was only intrigued as to whether this feature was due to a notionally acoustic reason, or because of original ease of manufacture. But I’ve measured up a couple of reeds this morning. One’s a Jeffries reed, which has had its slot filed to size, the other was a Lachenal reed of about the same size, which appears to have been simply stamped out. The rake angle of the slot (or Jim’s 2) is about 2-3 degrees on the Jeffries reed and less than 1 degree on the Lachenal. However there is a lot more taper (Jim’s 1) on the Lachenal, which seems to confirm your post that the two are inter-related. Both reeds are about 29mm long and the Lachenal tapers in width from 2.58 at the tip to 3mm at the clamp, while the Jeffries taper is only from 3.04mm to 3.1mm.
I have no idea if these are typical figures for the given makers production, but it does seem to suggest that mass production, even then favoured less of a rake angle. I could imagine that stamping reed frames with a fly-press would be easier if there was a little taper, otherwise the pressed frame would surely have the tendency to jam in the tool? Perhaps the tools themselves were more complicated than I imagine them – does anyone have experience with stamping out reed frames using a fly-press?

Adrian

[Chris Ghent]

I have not used press tools but I have seen a set. They are expensive to have made, one of the reasons some concertina makers have been people with the skills to make them. The ones I saw involve two operations per frame. The first stamps out the overall blank, the second holds that blank and broaches the slot in the centre, at the same time, at the end of the stroke, opening the aperture more at the bottom, the taper that has been the subject of this thread, while simultaneously allowing the brass that is displaced by this part of the operation to flow outward and create the outside bevel that secures the frame in the reedpan.

There would be no great push to create a taper just to allow the frame to come off the tool easily, disengaging the product from the die is routine in such operations, usually done by a device called a stripper plate.

The frames produced by the dies I saw needed work after the pressing operation, mainly filing of the top and bottom surfaces to remove buckling.

I don't know how much it would cost to get, say, 15 sizes of diesets made (Jeffries had about 9 sizes, Wheatstones maybe 15), but I'd be surprised if it was less than $30,000.

It can certainly be done with a fly press, Richard Evans once stamped a couple out to show me, and all of the factories would have used flypresses, but a small flywheel press is an easier bet and they can be cheap secondhand these days. If you want to know about these things in greater depth and more veracity, Dana who often posts in these pages has a huge depth of knowledge about press and diesets, and made his own set.

Chris

[ttonon]

Hi Chris,

I'm confused by your explanation of the die stamping.

The ones I saw involve two operations per frame. The first stamps out the overall blank, the second holds that blank and broaches the slot in the centre, at the same time, at the end of the stroke, opening the aperture more at the bottom, the taper that has been the subject of this thread...

I don't understand how a broach can open up the aperture (slot) more at the bottom than at the top, unless the broach is tapered and moves in a relative upward direction. This would require the broach to stop at a precise axial position. Although not impossible, I haven't heard of a broach being used in such a way, but I'm not an expert on this. The normal broach I'm familiar with that uses one stroke is a stepped cutter, moves in a direction perpendicular to the work piece, and cuts a slot with parallel sides.

I also understand that any stamping operation will produce a tapered hole, simply because the punch fits loosely within the die. The loose fit is required so that the punch does not jam, and the softer the metal work, the looser the fit. Thus, the angle of the bevel of the slot, after rough stamping, depends upon the mechanical properties of the plate material. Because of this, I can appreciate Adrian's general point that perhaps the bevel in the slot was originally a manufacturing artifact, which perhaps could've been taken advantage of, as a way to conveniently fit the tongue with precision, since it's only the top side of the slot that then required the most precise shape.

...while simultaneously allowing the brass that is displaced by this part of the operation to flow outward and create the outside bevel that secures the frame in the reedpan.

I'm really confused here. It's my understanding that a broach cuts metal and does not simply push it out of the way. Perhaps you're describing some kind of operation that molds metal, by deformation?

In thinking about all this, another question arises. Have reed makers used a metal working operation that, after rough cutting the slot in the reed plate by stamping, the slot is subsequently shaped to precision by inserting a mandrel, which has the (near) precise slot geometry, and then squeezing the entire plate from the outside, around the mandrel? The mandrel is then removed. With tapered mandrels, this process can conceivably result in a beveled, and/or tapered slot.

Your linking a taper on the tongue to a bevel in the slot intrigues me. I understand your basis for this, that both cause a wider air flow passage as the tongue descends through the slot, but this view is entirely a steady state view, and there may be unsteady effects that result in different acoustical behavior.

In your earlier post:

When there is relief in the window the returning reed does not come under so much pressure until the moment it breasts the narrowest point. This would effect lowest reeds least because they bend far enough to clear the slot completely and come under return pressure for a shorter period of their swing. Highest reeds are always in the frame.

Doesn't your reasoning cause one to conclude that a bevel in the slot would then more likely affect the sound of the smaller reeds, since, their tongues experience the greater changing air flow in the slot for a greater portion of their period of oscillation? The larger reeds spend less of their time in the slot region, and so are less affected by the changing flow area produced within the slot. This conclusion is not entirely different from my own, which examines basically the relative time portion the oscillating air particles occupy in the region within and near the slot. For the large reeds, air jets are formed, requiring that these air particles move far away from the slot, but for the smaller reeds, air particles vibrate in the vicinity of the slot for much more time, compared to the period of oscillation.

Best regards,
Tom

Edited by ttonon, 23 February 2012 - 01:56 AM.

[ttonon]

delete

Edited by ttonon, 23 February 2012 - 01:51 AM.

[Chris Ghent]

Oh dear, this will take a while..!

Hi Chris,

I'm confused by your explanation of the die stamping.

The ones I saw involve two operations per frame. The first stamps out the overall blank, the second holds that blank and broaches the slot in the centre, at the same time, at the end of the stroke, opening the aperture more at the bottom, the taper that has been the subject of this thread...

I don't understand how a broach can open up the aperture (slot) more at the bottom than at the top, unless the broach is tapered and moves in a relative upward direction. This would require the broach to stop at a precise axial position. Although not impossible, I haven't heard of a broach being used in such a way, but I'm not an expert on this. The normal broach I'm familiar with that uses one stroke is a stepped cutter, moves in a direction perpendicular to the work piece, and cuts a slot with parallel sides.

Tom,

I'm no expert either, though I have been tremendously impressed by what is possible with a dieset. Most of my information comes from Dana, and if you want good accurate information about frame stamping an email to him would get you more accuracy than I can provide. My reply related to the taper (I call it the relief) in the reed slot, and I described, though obviously not too well, the operation of the group of diesets owned by Richard Evans. In his operation the broach, which is largely as you describe it, is followed on the same shaft by a taper which widens the slot at the bottom just before it stops (the frame is upside down when broached). The broach does stop at a precise place every time, and this sort of precise operation is normal in diesets. The material displaced by the taper forming has to go somewhere, and it flows (yes it is very sudden but still it can be called flowing) sideways forming the bevel on the edge of the frame which is used to secure the frame in the reedpan. This is done relatively precisely because the part of the die holding the frame is shaped so as to control the flowed metal in the right shape.

I also understand that any stamping operation will produce a tapered hole, simply because the punch fits loosely within the die. The loose fit is required so that the punch does not jam, and the softer the metal work, the looser the fit. Thus, the angle of the bevel of the slot, after rough stamping, depends upon the mechanical properties of the plate material. Because of this, I can appreciate Adrian's general point that perhaps the bevel in the slot was originally a manufacturing artifact, which perhaps could've been taken advantage of, as a way to conveniently fit the tongue with precision, since it's only the top side of the slot that then required the most precise shape.

I think this underestimates what a good toolmaker can do with a dieset. The clearance between the male and female parts of a die is governed by the thickness of the material to be cut and the nature of that material, and there will be edge deformation but I don't think it inevitably results in a taper. My recollection is in a single toothed tool it is usual to aim for 1/3rd cut and 2/3rds shear. A broach by its nature is more like a series of progressive shavings.

Perhaps the best thing I can say is, a good toolmaker ends up with the shape he wants, and the relief we are talking about is way outside anything that is an accidental by-product. There is no way it is anything other than a desired shape.

In thinking about all this, another question arises. Have reed makers used a metal working operation that, after rough cutting the slot in the reed plate by stamping, the slot is subsequently shaped to precision by inserting a mandrel, which has the (near) precise slot geometry, and then squeezing the entire plate from the outside, around the mandrel? The mandrel is then removed. With tapered mandrels, this process can conceivably result in a beveled, and/or tapered slot.

That sounds like it would work, and I would be surprised if someone has not done it that way.

Your linking a taper on the tongue to a bevel in the slot intrigues me. I understand your basis for this, that both cause a wider air flow passage as the tongue descends through the slot, but this view is entirely a steady state view, and there may be unsteady effects that result in different acoustical behavior.

Granted; I was making a rough suggestion of parallel effect without expecting it to be exactly the same in all respects.

In your earlier post:

When there is relief in the window the returning reed does not come under so much pressure until the moment it breasts the narrowest point. This would effect lowest reeds least because they bend far enough to clear the slot completely and come under return pressure for a shorter period of their swing. Highest reeds are always in the frame.

Doesn't your reasoning cause one to conclude that a bevel in the slot would then more likely affect the sound of the smaller reeds, since, their tongues experience the greater changing air flow in the slot for a greater portion of their period of oscillation? The larger reeds spend less of their time in the slot region, and so are less affected by the changing flow area produced within the slot. This conclusion is not entirely different from my own, which examines basically the relative time portion the oscillating air particles occupy in the region within and near the slot. For the large reeds, air jets are formed, requiring that these air particles move far away from the slot, but for the smaller reeds, air particles vibrate in the vicinity of the slot for much more time, compared to the period of oscillation.

Tom, though it is obscured by the manifold subjects of these posts, the point I was making, I think, is that the shape of the slot is going to make a difference to all of the reeds, and I agree it will make a more difference to the shorter ones.

All of the talk about the possible accidental shape of the relief is specious, nothing about the design of concertinas is accidental. Opinion alert..! (No thorough testing done..!) The degree of relief is an adjustment on the operation of the reed, an adjustment which leads to different properties of volume, not just overall amplitude, but dynamic volume if you will, and to tone differences.

Edited by Chris Ghent, 23 February 2012 - 04:51 AM.

[Geoffrey Crabb]

Whilst not attempting to answer the original question or to become embroiled in discussion or to apply my usual kiss of death to a topic, I offer the attached which may be of interest.
[attachment=7285:Reed slotting and forging..doc]



Geoff

[Rod]

Whilst not attempting to answer the original question or to become embroiled in discussion or to apply my usual kiss of death to a topic, I offer the attached which may be of interest.
[attachment=7285:Reed slotting and forging..doc]



Geoff

December 2008 you posted details of a new 12 key Midget, accompanied by the all-time understatement 'I didn't have one so thought I should knock one out'. Hurry up with the book and then we can all 'knock one out' !

[Andy Holder]

Might it be to allow the reed to return more easily?

On the downwind stroke the air flow is pushing the reed and supplying energy.
On the upwind stroke the reed has to return against air flow. If it returns to a parallel slot it faces close to full air pressure as soon as it reaches the bottom of the slot and loses energy in overcoming this until it clears the slot.

I imagine this would make it more likely to choke, and also introduce more harmonics due to asymmetry in the swing cycle.

With a taper, air can bleed around the reed until it is almost back to start position thus the reed loses less energy.

On the downwind stroke the air pressure on the reed will also drop off more rapidly once it starts to move, as air bleeds around it. This will result in a less sustained push and less energy on the downwind stroke, again improving symmetry and tendency to choke.

My jew's-harp has a slot with an edge in the middle, and a bit of relief on both sides. My understanding for the rationale (at least partially) is that having sharp edges in the airflow (on the reed & in the slot) creates more turbulence in the stream, producing more high harmonics for a fuller, brighter tone.

Is everyone here even talking about the same thing?

• There's "taper" from the base of the reed to its tip, i.e., being normally wider at the base (where it's fastened) than at the tip (the freely swinging end).
• And there's the "bevel" or "undercut", in which the slot of the reed frame is wider at its "under" side than at the "top".

I'm a bit confused, but I think you two are talking about the second, while aybee and some others are talking about the first.

One point that I don't think has been addressed here is whether the first has an effect on the quality of the sound. Seems to me that it does, as I understand that the rare "clarionet" concertinas -- with a sound intended to imitate a clarinet, bassoon, or other woodwind reed instrument -- have reeds that are wider at the tip than at the base, often described as "spade-shaped". And I remember seeing in the book The American Reed Organ drawings of experimental reeds of even more complex design, including one in the shape (looking from above) of a cross and one like a forked snake's tongue. No idea what those latter two sounded like, though I believe they were intended to produce unusual sound qualities.

Jim, I just measured a set of Wheatstone English reeds and frames very accurately and it turned out that some of the reeds were tapered and some were parallel. Some "pairs" of the same note would have a tapered one and a parallel one, not always the same way. It's my conclusion that, as the frames were stamped and irregular, the reeds were just hand filed to fit the slot and sometimes they would end up tapered. I don't believe there's any relevance in the shape of them, although I'm happy to be proved wrong!
Andrew

[Andy Holder]

===

Edited by Andy Holder, 23 February 2012 - 04:54 PM.

[Chris Ghent]

Nice explanation Geoff, better than my clumsy attempt...

Chris