Spring Winder

I made a simple machine for winding concertina springs, inspired by Bob Tedrow‘s video.


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It has a drum with a mandrel sized for the desired coil diameter and a hook on the outside, driven by a crank handle. The small step at the base of the mandrel helps to get the first turn of the coil tight. The adjustable guide plate isn’t strictly essential, but it helps a bit with consistency.

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The raw spring material; 22 S.W.G. (about 0.7mm) phosphor bronze spring wire. It bends easily, is fairly corrosion resistant, and I’m told it lasts a lot longer than brass. At some point I’m planning to experiment with stainless spring steel and other diameters, but I’m sure the phosphor bronze is going to work fine for my initial prototype instrument.

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Step 1; use needle nose pliers to bend a right-angle that will form the ‘pin’ that you push into the action board:

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Step 2; insert the wire into the machine as shown. It’s important that the hooked end is parallel to the face of the drum:

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Steps 3 and 4; turn the crank handle clockwise about 2 1/4 times, then cut the wire off, using the guide plate to gauge where to cut.

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Step 5; use small round nose pliers to form the hook:

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Step 6; use needle nose pliers to bend the hook over at a right angle:

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The finished spring:

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Here’s a quick video of the process:

Sometimes it’s necessary to use an opposite-hand spring because of limited space on the action board. You make these in the same way but doing all the bends the other way and turning the crank handle anticlockwise:

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A few experiments with various arm lengths:

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Prototype Pads

Concertina pads are small discs that cover holes in the action board; when you press a button, it causes a pad to lift off its hole, which allows air to pass through a reed and produce a note. They are made from a sandwich of leather, felt and card. The leather forms an airtight seal against the hole, the card provides a rigid backbone and a surface for the action lever to attach to, and the felt acts as a buffer between the two that stops the pad making an audible slapping sound when it closes quickly.

It took quite a few experiments to find a combination of materials, glue, and procedure that produces satisfactory pads. Along the way I made quite a few pads that fell apart, were too hard or too spongy, and/or were too thick or too thin.

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A pad ‘sandwich’ after gluing:

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I eventually settled on hide glue with some urea added to extend the open time a bit. I soaked apart an antique Lachenal pad and I’m 99% sure it was glued with hide glue. PVA would probably work too, but when I tried it, it stuck well but it seemed to soak into the felt and make it harder. I know others have used sprayable contact adhesive successfully, but it barely stuck at all for me. There’s a bit of a knack to applying just the right amount of glue, and it’s important to brush it onto the card/leather, not the felt, otherwise it will soak up far too much glue and go hard when it eventually dries. Clamp the sandwich as lightly as possible and take it out of the clamp after an hour to avoid permanently compressing the felt. Leave it at least a few hours to dry before punching the pads out.

The leather is thin smooth sheepskin skiver, with the hair side out. The card is 1mm greyboard (I also tried millboard, but it turned out to be made of two layers that delaminated when I punched the pads out). I tried five different wool felts before settling on this one, which the supplier describes as 1.5mm 25 S.G., though it starts out significantly thicker than that and compresses down a bit when you glue it.

I’m punching the pads out using Priory wad punches (carefully resharpened), a lead mallet, and an anvil made from the smoothed end grain of a beech log soaked in boiled linseed oil.

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It works best to punch with the leather side up, otherwise the card distorts and doesn’t cut cleanly.

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It’s important to keep hammering until you’ve cut through the card all the way around.

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A new pad next to a ‘retired’ antique Lachenal one; the new one is a bit thicker and softer, but I think it will quickly compress down to about the same thickness.

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Bastari Repairs

I just finished fixing up a Bastari G/D Anglo for a friend who plays for Anonymous Morris. The aim was mainly to repair a few faults and tune it up, to make it more playable rather than carry out a complete restoration.

The first problem was that the action boxes had split apart in several of the corners, so I cleaned up the joints and glued them back together, adding reinforcing blocks to strengthen them. This was a bit of a delicate job because they were originally constructed with PVA glue and I couldn’t remove any significant amount of material from the joints when cleaning off the remains of the old glue or they would have got smaller and would no longer fit the rest of the instrument.bastari_1

The chrome-plated brass end plates were a bit grubby so I gave them a quick polish:bastari_2

This instrument’s Achilles heel is the aluminium pivots where the buttons are attached to the action levers. Note that these are different from the rubber tube type commonly found on Stagi instruments. Most of them were rather wonky, and the most-used buttons were sloppy due to wear; a few were almost worn through:bastari_3

After discussing the problem with the client, I agreed to make replacements for the most-worn levers. I cut the new levers from 1mm brass sheet with riveted pivot points, so they are unlikely to wear out again. After designing the two sizes of lever and the button insert in CAD, I printed a template on sticky paper and cut them out by hand with a jeweller’s saw.bastari_4

I re-used the top parts of the buttons, which were made from chrome-plated brass with the aluminium pivot glued into a hole in the bottom. The first step was to break off most of the pivot with a pair of needle nose pliers:bastari_5

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Then I put the button in a drill chuck in the lathe and drilled into it with a centre drill:bastari_7

Then a 3mm drill (this was a tiny bit bigger than the original hole, so it left a nice clean surface on the inside of the hole):bastari_8

At a certain point, the drill stopped cutting; this meant that the tip of the old pivot had come loose and was stuck on the end of the drill bit. After withdrawing the drill and removing the loose piece I was able to finish cleaning up the rest of the hole:bastari_9

I sawed the new pivot pieces slightly wide, then carefully filed them down until they were a snug fit in the hole:
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I glued the new pivot pieces in with Araldite Rapid Steel (an epoxy resin that is specifically formulated for gluing metal):bastari_11

I found it easier to work on the action if I removed all the levers apart from the one I was working on at the time. I glued the new levers to the original pads using hot melt glue (this seemed to be how it was done originally), fitted the spring, put the end plate on, marked the position of the hole on the lever, took it apart, drilled the rivet hole in the lever, cut it shorter, riveted the button on, put it back together, and bent the lever until the button was directly below the hole.

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Here’s a quick video clip of me riveting a button to a lever:

And here’s the resulting pivot. I actually made a ‘snap’ tool from hardened silver-steel to form domed rivet heads, however I found that it inevitably made the joint stiff if I hammered it enough to take out all the play. By using lots of light taps with a small ball peen hammer instead, I was able to make pivots that work and feel just right. Note that the mushroomed end of the rivet doesn’t turn; it expands enough so that it is a tight fit in the lever, but there is just enough play in the joint for the pivot to turn smoothly without any noticeable wobble.

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This video shows the difference between a sloppy worn-out pivot and one of my improved brass riveted ones:

As well as replacing ten of the levers, I adjusted the remaining 21 as best I could, straightening and tightening them up as much as possible. Rather a fiddly, painstaking task, and it’s impossible to get them perfect without replacing them all.bastari_13

The bellows had quite a few worn corners, some of which were leaking air, so I glued thin patches on them. I tried to dye the new leather to match the old, but it didn’t work very well: I managed to get the leather slightly darker, but it seemed to quickly reach a point where it didn’t want to absorb any more of the dye.

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Tuning the instrument proved much more difficult and time-consuming than I expected. Some of the reeds were no trouble, but many of them behaved illogically, randomly going flat and muffled, then suddenly going sharper again when I fiddled with them or just after playing them for a while. In hindsight, stiff/sticky valves were mostly to blame for this. Some of the reeds were rather dirty; this one went five cents sharper when I wiped the sticky black dust off it:bastari_15

There was one reed that nearly had me pulling my hair out: it kept going flat by six cents whenever I tightened the instrument’s end bolts down. After trying many different things, I eventually worked out that there wasn’t quite enough clearance between the reed tongue and frame on one side. Somehow, tightening the end bolts down was bending the sound board and applying a force to the reed frame that distorted it just enough to cause the tongue to slightly graze the vent side, which made it sound flat and slightly buzzy.

The finished instrument ready to go back to work, playing traditional English dance music:bastari_16

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Bidirectional Reed Experiments

Recently I was asked to try to come up with a concertina reed that works in both directions, or at least to figure out why it hasn’t been done before. Ordinarily, a free reed only speaks when you suck air down past the tongue, into and through the vent in the frame. Most concertinas have a pair of reeds controlled by each button; one inside the reed chamber that only sounds on the pull stroke and another mounted on the underside of the reed pan that only sounds on the push stroke. Anglo instruments take advantage of this to play different notes on pull and push (this is known as bisonoricity), whereas English and Duet instruments play the same note in both directions so they need a pair of identical reeds for every button. If it was possible to make a bidirectional reed that worked as well as two standard reeds, it could potentially enable unisonoric instruments to be made smaller, lighter, and cheaper.

The way I went about solving the problem was to first build what was pretty much a standard reed in an oversized frame and check that it sounded normally in the suck direction, then screwed on a roughly horseshoe-shaped plate that fit around the tongue. I didn’t expect this to work because there was no way for a significant amount of air to get past the tongue to start the oscillation cycle, and indeed it didn’t.

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I also modified my bellows bench a little to allow me to block up the standard dovetail socket and screw the new oversized frame to it elsewhere, and provided a means to block the one-way valve that normally releases air when I raise the bellows so that the rig only works in the suck direction.

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Next I took the horseshoe back off and started experimenting with filing away various parts of the bottom of the horseshoe vent around the tongue, to provide some space for air to get to and past the tongue and allow it to start. Eventually I got it to sound, albeit poorly, in the suck direction, and it even made a tiny bit of sound in the push direction.

I had a theory that the triangular profile resulting from filing the underside of the horseshoe vent was causing the airflow to be cut off too gradually in the blow direction, so I next made a new horseshoe piece, this time with a square-sided recess milled into the underside so there was air space all around the tongue. This was supposed to cut the flow off more cleanly when the tongue swung up into the horseshoe vent.

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This did work a little better, however it was very inefficient, very quiet, and worked much better in the suck direction than the blow direction. I figured that the reason it worked unequally was because the reed tongue was profiled only on the top surface, so when it passed into the bottom vent it cut the airflow cleanly and suddenly whereas when it passed into the top vent it cut it progressively from the tip towards the root.

In order to try to solve this asymmetry, I built a second, more complicated, reed. On this one the reed tongue is set into the bottom frame by half the thickness of the reed stock, it is profiled equally on top and bottom of the tongue, and I also restricted the air pocket to the last third of the tongue, which I tried to profile fairly flat so that it cuts the airflow fairly cleanly in both directions.bidi_reeds_4

The second reed was the most successful prototype I built, however it revealed the biggest flaw with the idea. When set up carefully it works pretty equally in both directions, however the amplitude is very limited compared to a standard reed:

I believe I now understand the reason for this, however it is a little tricky to explain. Before starting my experiments I had observed that with a standard reed playing at normal volume, the tongue swings well above and below the restriction point at the entrance to the vent. I imagined that with the bidirectional reed, it would swing past both restriction points and generate a similar amplitude level, perhaps with a different tone. This was based on a couple of misunderstandings about how reeds work.

My current understanding of what happens with a standard reed when it first starts up is that the tongue gets drawn down towards the frame (it needs to be set such that at rest there is a slight gap between the tongue and frame so air can start flowing). I don’t fully understand the physics behind why this happens, but it seems to me that the faster the airflow into the vent, the harder the tongue gets pulled down. The tongue descending towards the vent opening restricts the airflow into the vent, the force pulling the tongue down reduces, and the tongue springs back up, eventually peaking slightly higher than its rest position. Because it is higher, the gap between the tongue and the frame is larger and more air is able to flow through it than on the first cycle, so it gets drawn down a bit further, and springs back a bit higher than before. Over the course of a number of cycles, the amplitude builds up and up until the tongue is swinging a long way below the top of the vent. In order for this build-up to work, it’s important that every time the tongue swings a bit higher, it results in more air flowing through the vent, which causes the tongue to be pulled down harder and the amplitude of the oscillation to increase. Eventually the oscillation reaches an equilibrium level that depends on the pressure differential between the top and bottom of the reed frame. If you squeeze the bellows harder, the tongue oscillates to a greater height and the ‘packets’ of air being chopped up by the tongue passing through the frame are larger and more energetic, which results in a greater volume of sound from the instrument.

What goes wrong with my bidirectional reed that prevents it developing a decent amplitude at normal bellows pressure is that the second vent restriction, the one ‘above’ the tongue (whichever direction that happens to be), cuts off the air supply whenever the tongue tries to swing higher than the opening into the second frame. It’s impossible for the amplitude of the oscillation to ever build up any higher than the second frame, because it restricts the air supply as the tongue swings higher instead of allowing more air through. It is a lot like the governor on an engine, which throttles the fuel supply whenever it tries to exceed a certain speed.

It is possible to increase the amplitude at which the limiting occurs by increasing the distance between the two vent openings inside the reed, however there is a limit to how far you can take this. If the distance is too wide, the reed oscillations take several seconds to build up to an audible level, or never start up at all. It also becomes impossible to deliberately play the reed very quietly: you end up with a reed that has essentially no dynamic range.

To make matters worse, as well as the limited volume issue, there are several other disadvantages to this type of reed:

  1. They seem to be less efficient (i.e. they use more air than a standard reed operating at a similarly low amplitude), possibly because the way it is constructed to allow it to perform equally in both directions has the side effect of not cutting the airflow very cleanly in either direction.
  2. They are considerably more difficult to make than a unidirectional reed, probably something like 75% of the work of making a pair of standard reeds. A lot of the extra work has to do with making both frames a tight fit around the tongue without catching on the sides. Because nearly all of the cost of a hand-made reed like this is in labour time, it wouldn’t be a large cost saving to make an instrument with half the number of bidirectional reeds.
  3. They are significantly bigger and heavier than a standard reed because of the need to be able to screw the two parts together; you would save a little compared to a pair of standard reeds but not as much as you might think.
  4. There are a bunch of issues around the fact that what you would call the ‘set’ on a standard reed is fixed at manufacture-time by the relationship between the height of the recess and the thickness of the tip of the tongue. You can’t easily alter it deliberately, and it is possible to alter it accidentally as a side-effect of tuning the reed. It’s also important for the tongue to be set precisely central between the two frames, otherwise it starts poorly or not at all in one direction or the other.
  5. I don’t know for sure, but I suspect this design would be more susceptible than a standard reed to getting dust and fluff caught inside it and impeding its operation, because the air gets forced through a narrow recess inside the reed.
  6. It goes without saying that this type of reed is useless for an Anglo instrument because it produces the same note in both directions.

Following up on a slightly different line of inquiry, I made two final experimental reeds, one which only had a rectangular recess right at the tip, and another which was very similar but with a triangular recess instead. Neither of these worked as well as the second reed, I suspect because they only have a tiny amount of space for air to squeeze past the tongue. They sound in both directions (just about), but are very inefficient and quiet.

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Here is an audio recording I made of the four experimental reeds plus a standard reed for comparison. The first reed had the second horseshoe fitted.

Although this work didn’t lead to a usable product, it was still a useful exercise for me in that I believe I now have a significantly better understanding of how concertina reeds actually work.

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Punching Washers and Grommets

I decided I wanted to try making some punch tooling in order to manufacture a couple of the parts involved in a traditional concertina action: the felt washers that go under the buttons and the leather grommets that screw onto the ends of the action levers.

As well as the big Smart & Brown 2-ton toggle press mentioned previously, I also have a little 600N Brauer one (if my calculations are correct, the big one is rated to deliver about 30 times the force of the little one). I got it second hand some time ago, with some odd custom tooling attached to it that I never figured out what it was supposed to do. Here it is after removing the tooling and cleaning it up a little (yes, that is an old gear knob on the end of the handle – actually quite a nice addition so I left it on):

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Because the throat height of the press is considerably more than the thickness of a piece of felt or leather, I turned up a 50mm tall spacer block from scrap 1″ mild steel bar. It bolts to the table of the press and has an M8 threaded hole in the top for the punch anvil, and a cross hole for the ejection of waste punched through the hole in the middle of the anvil.

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I needed to cleanly bore out the inside of the felt washer punch, so I ground a simple D bit from the 1/4″ shank of a broken HSS end mill:

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I drilled most of the waste out first, then used the D bit to open it out to 1/4″ and cut a flat bottom on the hole. At this stage I also drilled a 1.5mm hole for the centre pin:

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I used the compound slide to turn the tapered sections of the top punches, stopping while the edge was still fairly blunt. After hardening and tempering, I put them back in the lathe and used emery paper to clean up the taper and sharpen the edge.

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Threading the other end of a punch with an M8 die so it can screw into the press arbor:

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The anvil and felt washer punch installed in the press. I made the half-nuts that are used to lock the tool at the desired height by facing ordinary full nuts on an arbor.

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Here’s a quick video clip showing the felt washer punch in use:

This shows where the washers go on the buttons, to stop them making a clacking noise when they bottom out:

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A nice stockpile of washers for my first few instruments. I made these from a sample piece of ‘baize’ woven wool cloth as used on gaming tables. I also have several other sample pieces in various different colours. I think the original washers may have been made from an actual fine, thin felt rather than a woven cloth, though – I need to get hold of some samples to experiment with.

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The first anvil I made had a design flaw: the hole through the middle for the ejection of waste material was drilled 1.5mm diameter all the way through the tool. In practise it quickly became constipated and I had to repeatedly remove it and drill out the waste. The one on the right is a second, improved version that is relieved to a larger diameter until a couple of mm from the top surface:

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Here are all the punches and anvils I made. The first one is the felt washer punch. Inside it is a couple of layers of spongy foam and then a couple of felt washers; with careful adjustment of the pressing force this seems to be just right to prevent the washers getting stuck inside. The second one I had optimistically hoped might work the same way, but the grommets just got stuck inside it and wouldn’t come out, so I instead decided to use it to punch out the centre hole and mark the location of the outside of the grommet, then switch to the third punch which has a slot milled in the side to allow the grommets to be pushed through and removed from the top.

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Here is a video clip showing the leather grommet punches in use. Note that in the video I was using 2.5mm veg tan cowskin, however I subsequently found that I got much better results from 4mm leather instead (the 2.5mm leather compressed down to 1.5mm in the punching process and the 4mm to about 3.2mm). I also removed the stripper plate seen in the video because I found it was getting in the way and causing more trouble than it was worth:

This shows where the leather grommets go inside the instrument. They screw onto the end of the lever arm (which is lightly threaded), then glue to the samper disc on top of the pad:

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A couple of hundred leather grommets for my first few instruments:

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Although these are fairly trivial parts, it certainly feels like progress to be stockpiling significant quantities of production-quality parts that I have made using my own tooling.

UPDATE: I’ve since got hold of some 0.8mm piano bushing cloth and punched more washers from it:

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The piano bushing cloth is thinner, finer, and more tightly woven than the baize. Unfortunately I’ve only been able to find it in bright red with a white core. I may experiment with dyeing some of it black.

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Website News

I’ve recently made a few small improvements to the website, the most significant being that I have replaced the old email subscription system with a new one that will hopefully prove more reliable. If you previously tried to subscribe to the site by email and it didn’t work for you, please try again.

A small addition you may notice is that each post now has a ‘like’ button below it. This is simply a very easy way for you to let me know if you read and enjoyed a post, thus encouraging me to write more in the future.

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Reed Tongue Shear

When I made my first prototype reeds, I found that it is nearly impossible to cut 0.9mm hardened and tempered spring steel with hand shears. After I obtained and restored a heavy duty industrial bench shear that was strong enough to cut the metal, I learned that it is extremely difficult to accurately and consistently cut narrow, tapered strips to a specific width and angle. Because the fit of the tongue to the frame is crucial to the performance of the reed, the only thing I could do was to cut the tongues significantly wider than necessary and spend a long time painstakingly filing them down to final fit. The bench shear also had a tendency to bend and sometimes even twist the tongues, making it necessary to carefully straighten them out before profiling.

A solution to my problem came in the form of Geoffrey Crabb’s description of a press tool his family has used for all the reeds they have made since Victorian times. I made a few small changes to the design, mainly because my press is a different type1, which necessitated rotating the blades through 90 degrees.

This was how my press looked when I first acquired it. It is a Smart & Brown H5 2-ton toggle press. Although it looked cosmetically rather tatty, it was fully functional with not much wear.

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And here is the restored press with the shear tool I made for it installed:

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I made the blades from 15mm thick O1 tool steel that I hardened and tempered myself, and the holders are made of various oddments of scrap mild steel that I stick-welded together (my welds may not be very pretty but they are strong enough!).reedtongueshear3

This thing bolted onto the bottom of the moving blade is the clever part. It has a 1mm tall slot with a moving spring-loaded brass plate inside it that acts as a width stop and ejector.reedtongueshear4

You insert a piece of stock (already sheared roughly to length on the bench shear) into the slot until it stops against the brass plate. The two brass thumb-nuts control the position of the brass plate, thus setting the desired width and taper angle of the tongue. After pulling the press handle to shear the metal, the tongue is now trapped inside the slot, so you pull the plate towards you using the two bent tabs, ejecting the tongue, then a pair of springs pulls the plate back against the adjuster nuts. See this brief video for a demonstration:

I’ve found it helps to have a box on my lap to catch the sheared-off stock and the ejected tongues before they fall on the floor!

With the new tool I was able to cut these four identical tongue blanks in less than a minute. They still need deburring and a bit of finish-fitting with a file, but much, much less than when I was trying to cut them with the bench shear.

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Note that, as Geoffrey Crabb pointed out in his description of the process, it is preferable to turn the stock over between each cut so that the burrs are both produced on the same face of the tongue blank rather than opposing corners. The face with the two burrs on it becomes the bottom of the tongue, because once you lightly stone the burrs off it leaves you with a nice sharp, square edge.

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Reed Prototypes Part 2: Tongue

The way a free reed works is that a tongue made from a springy material (usually spring steel or brass) is made to oscillate through a close-fitting window in a metal frame by the flow of air through the reed. Each time the tongue passes through the tight part of the frame it briefly interrupts the air flow. This regular chopping-up of the air flow produces a tone with a significant harmonic content (it’s a long way from being a pure sine wave).

I’m using hardened spring steel for my reeds (IIRC it was 0.8mm thick on this size of reed), which I found practically impossible to cut with hand shears, so I bought an old bench shear on eBay. I got it cheap because it was seized up with rust and the blades were blunt and dented, but it is a nice heavy-duty machine:

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After restoration, it works really well (though it would be nice to have an extension tube on the handle):

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I need to come up with a better way of cutting the strips consistently to the right width. To complicate matters, they are slightly tapered. Initially I scribed them and lined them up under the blade by eye, which worked better than I expected but was rather fiddly and time-consuming.

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The shearing action bent the tongue slightly so I straightened it before doing any more work on it:

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Next I cleaned up the edges by draw-filing while it was held in a toolmakers vice:

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It’s important to make the tongue a very close fit in the frame, but not so tight that it’s prone to catching if the reed pan expands and presses on the sides of the frame:

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A low-power back-lit stereo microscope is a big help with fitting the tongue to the frame. Although the gap looks off-centre in this picture, that’s because you’re only seeing the view from the right eyepiece.

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In a concertina, the tongues are usually not a consistent thickness along their length: they are profiled so as to bring the pitch up or down and to balance the volume of the reeds across the range of the instrument. Because I don’t fully understand all the parameters yet, I decided to start out by copying the profiles of the reeds in an antique instrument. I took the tongue I was copying out of its frame and measured it in several places with a point micrometer (I found it wasn’t difficult to put it back in the same place, and it still produced the same pitch afterwards).

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I did the profiling by hand using a triangular Bahco saw file and an Eclipse hand vice, on top of an oak block with a shallow step cut into it. You can tell roughly what pitch you are at by ‘pinging’ it. I found, at least with this size of reed, that it is very easy to take a hair too much thickness off the belly area and the pitch suddenly drops by a couple of semitones. You can bring it back up by taking a lot of thickness off the tip, but then you have a weak reed that sounds slightly odd.

After clamping the profiled reed into the frame, you have an extra bit of tongue sticking out of the back of the reed that needs to be removed (you deliberately shear the tongue too long so you have something to grip while profiling and fitting it). Because it is hardened steel, the extra bit is very easy to break off, and the fact that the clamp doesn’t quite reach the end of the frame means that the sharp stub doesn’t stick out significantly past the end of the reed:

Here I am doing the initial rough-tuning of the reed before trying it in the instrument. Note that removing some metal from the belly (using a 600 grit diamond needle file) caused the set of the tongue to alter, i.e. the tip bent down slightly. This caused the reed to choke the second time I tried to sound it. There needs to be a slight gap between the tongue and frame when it’s at rest or no air will flow through it and it won’t start oscillating by itself.

From left to right, we have the original antique Lachenal reed I was copying, my first working reed (using the best of the aluminium frames), and my first brass-framed reed:

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My first brass reed in the instrument:

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The profiling of this first reed isn’t a perfect copy of the original: rather than being a smooth curve from the belly up to the tip, the profile curves up too sharply and then plateaus before the tip. The effect of this is that although the pitch is right and the dynamic range seems OK, the tone has less upper harmonics. When I compare it in the instrument to the original reed next to it, it sounds ‘softer’ with less of the piercing ringing overtones of the original. I suspect this is because most of the bending action is happening near the clamp rather than spread out along the full length of the tongue. Something to work on improving in my next prototype!

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Reed Prototypes Part 1: Frame and Clamp

Recently I made my first prototype concertina reeds. There’s a lot to write about so I’m going to divide it into two articles, this one will cover the frames and clamps, and the next one will cover the tongues.

My plan was to make a drop-in replacement for one of the low ‘B’ reeds in my vintage Lachenal English. I think this instrument was probably one of Lachenal’s higher-end ‘broad scale’ models, because I also have another steel-reeded Lachenal that in many cases has narrower reed tongues in the same pitch. I’m not totally sure why the narrow scale models existed or were originally cheaper than the broad scale equivalent (the extra metal and labour is fairly trivial). They were probably quieter at the top end of the dynamic range, which might make them better for a student instrument.

I understand Wheatstone’s earliest reeds were made totally by hand, piercing them with a jewellers’ saw and cleaning them up with files. This must have been very labour-intensive, highly-skilled work, and prone to inconsistency. At some point fairly early on, perhaps when Louis Lachenal was hired to mechanise production(?), they changed to using fly-presses and dies to punch out the reed frames. This was much faster, worked well, and the presses could be operated by relatively unskilled workers, but the disadvantage is that precision dies are very expensive to make. To save on tooling costs, instead of making a different set of dies for every pitch of reed, they made do with a handful of sizes and made up for the gaps between them through careful tongue profiling. Until relatively recently, the need to invest in a set of press tooling was a significant barrier to entry for new reedmakers.

Enter CNC machining. I understand other makers have successfully used laser cutting or possibly wire EDM, but I have my own small CNC milling machine so that is the process I am going to use. It is fairly slow (certainly compared to a a press tool), but it works pretty well and I hope to get to the stage where I can load in enough brass for half an instrument worth of reed frames, and set it going with minimal supervision while I work on another task. As well as cutting out the shapes of the frames and clamps, it can also cut the vent slots (albeit with filleted corners), drill the clamp holes, engrave the note labels and a logo, counterbore the clamp screw holes, and even chamfer the top edges of the frame so they fit nicely into the dovetailed slots of the reed pan. Initially I’m planning to copy all the dimensions of my prototype reeds from the Lachenal instrument, but in future when I understand the design parameters better I will be able to make frames that are the optimal size for each pitch.

My first attempts at milling frames were using scrap aluminium. It took me quite a few failed attempts before I got one that seemed pretty good (the antique Lachenal frame I was copying is on the right):

aluminium_reed_attempts

Next I moved onto brass prototypes, immediately running into problems with it cutting very badly and breaking 1/16″ end mills:

failed_brass_reed_shoe

A microscope view of an end mill with clogged flutes, from a run that I aborted before it snapped:

clogged_end_mill

I think the reason for my problem was that the chips weren’t clearing from the slots properly so on subsequent passes they were getting re-cut and generating a lot of heat. I experimented with a lot of parameters, but basically what worked was making the depth of cut shallower, increasing the spindle speed to 10K RPM (the maximum my machine’s spindle can handle), significantly increasing the feed rate (to make bigger chips), and adding a compressed air blast to blow the chips away. I also changed from two flute HSS bits to three flute cobalt bits, though I’m not certain that helped with the chip clearance (it did allow me to increase the feed rate a bit more). It also proved necessary to make some proper mechanical clamps to hold the plate to the spoil board, because double-sided tape wasn’t holding it securely enough:

sheet_metal_mill_clamps

Here is a (21 minute long) video of the process of milling a single reed shoe prototype. Don’t bother watching the whole thing unless you’re really fascinated! This isn’t quite the final program: I subsequently altered the bevelling operation slightly so that the frame wedges more securely into the reed pan.

The CNC program includes small tabs that prevent the parts coming loose during machining. Afterwards these need to be manually cut. I found that it was possible to break them out with a small chisel but it left rough stubs that I then had to clean up with a file, so I changed to cutting them with a jeweller’s saw:

cutting_reed_frame_tabs

Because I cut the vents using a 1/16″ end mill, this leaves 1/32″ radius fillets in the corners, which should ideally be dead sharp. I’ve been manually cleaning these up using a fine square needle file with one edge ground smooth. I put the reed frame over the small square hole in my bench peg (see previous photo), hold the safe face of the file flat against the end of the vent, and carefully file sideways into the corner until it’s as sharp as possible without leaving a nick:

reed_vent_squaring

The clamp screws I’m using are a bit smaller than the originals; they are M1.6, stainless steel, with 2.5mm diameter allen heads:

clamp_screw_comparison

In my testing they are strong enough for the purpose and take up less space than the originals, and the finer pitch and allen heads make them easier to tighten and loosen without damaging them.

When tapping the clamp screw holes in the frame, it’s very important to keep the tap perpendicular to the hole. After researching tapping machines and complicated guides, I came up with this simple method that works surprisingly well (though I still managed to break a tap the first time I tried to tap one of the brass shoes!):

I added counterbores to the holes in the clamps because it was easy to do and significantly reduces the height of the reed without weakening the clamping ability. It also improves the accuracy of the location slightly. Because I was already using an engraving operation for the note labels, I added a simple brand to the clamp (HC=Holden Concertinas):

reed_clamp

Because the screws start out a couple of mm too long, I put them in the frame and grind them almost flush with the bottom of the frame, then finish them off with emery paper on a sheet of glass:

grinding_clamp_screws

One of the defining characteristics of traditional concertina reed shoes is that the underside of the vent is relieved (i.e. the bottom of the slot is slightly wider than the top). My current understanding is that this allows the reed to work properly even at very low bellows pressures, i.e. it enables you to play quietly if you want to. It also has an effect on the tone. I’m not doing this on the milling machine because there are good reasons to cut them out from the top and it would be a bit tricky to turn them over and accurately register them for an extra operation. Instead, I made a special jig that allows me to file the vent to a consistent angle using a flat needle file with two safe narrow edges.

The clamp part of the filing jig started out as an old war-surplus hand vice with damaged jaws:

vent_filing_jig_1

vent_filing_jig_2

I trued up the jaws and modified the profile of the front jaw so that there is room for the file to tilt down below the level of the back jaw:

vent_filing_jig_3

Next I added an adjustable brass frame and a PTFE roller to guide the file, as shown in the following video. I align the top edge of the vent with the top of the back jaw, paint the inside of the vent with a black marker pen, and file until I’ve almost but not quite removed all the ink.

Here we have my first brass reed frame in my Lachenal reed pan. You can see how much lower-profile the new screw heads are: I think this might help with air flow inside the reed chambers. It took several prototypes before I was totally happy with the tightness of the fit in the dovetailed slot. There is a small area around the clamp that isn’t fully bevelled, giving a nice friction fit without compressing the sides of the frame adjacent to the vent.

reed_frame_finished

finished_brass_reed_frame

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Tuning Bellows

Recently I’ve been working on making myself a new set of tuning bellows. The first tool I made towards this goal was a new craft knife for cutting leather and card. I ground it from a piece of HSS machine hacksaw blade, because I had read that the steel is more wear-resistant than a simple carbon steel, and I wanted to test the theory.

craftknife

I’m not convinced it holds an edge better than a well-tempered O1 blade, however it does work pretty well. Unfortunately the spalted beech scales (glued on with epoxy resin) popped off after a couple of days. It would have been better to have riveted them on, however drilling holes in hardened HSS is easier said than done. For the time being I have just bound them on with a length of thick elastic.

On a roll with the knife-making, I next made myself a leather skiving/paring knife from the same materials as the craft knife:

skivingknife

This video shows how I use it:

I do of course also have a Schärf-Fix 2000 skiving machine, which I wrote about previously:

The Schärf-Fix is good for long strips, whereas the knife is better for skiving small pieces (particularly gussets) and odd bits here and there. Both tools are tricky to use, and I wasted a frustrating amount of leather while getting to grips with them. The Schärf-Fix has a tendency while edge-skiving a long strip to suddenly dig in and cut a chunk out of the strip. The key is that the blades have to be absurdly sharp, because the thin leather tends to stretch badly if you have to use any significant force to pull it through the machine. I need to spend some more time figuring out a way to resharpen the disposable blades (stropping didn’t help much), or I’ll end up going through at least a couple of them per concertina.

I used my Käfer Dial Thickness Gauge to make sure I was paring it consistently:

I needed to make end frames for my bellows, so I first needed a way to accurately make the corner reinforcing blocks. Here’s the jig I came up with. There’s a bit of a knack to using it, but the results aren’t bad:

cornerblockjig

And here’s one of my new corner blocks next to an antique Lachenal one:

cornerblock

I cut the sides of my bellows frames from 9mm plywood using my Nobex Proman 110 mitre saw, and glued them together with hot hide glue:

nobexproman

After a bit of shaping, I checked that they fit in the scrap Jeffries bellows I was copying my dimensions from:

bellowsframes

Next came the bellows mould. This proved quite a large sub-project in its own right. It has six forms (one of which is split in two to make it possible to remove the forms), screwed to a hexagonal core, suspended from a stand. Making the forms was the hardest part. I started by gluing blocks of pine to strips of plywood, with the grain running across the form, being careful to avoid including any large knots:

bellowsmould1

Then I used the bandsaw with the table tilted over at 45 degrees to relieve the under-sides of the forms:

bellowsmould2

Then I used the CNC milling machine to cut the valleys into the top sides of the forms (video sped way up: it actually took about an hour to machine each form):

After I had spent days making all six forms, I laid them out next to each other and realised I had made a silly mistake: five of them were spaced wrong, and in fact all of them were pitched slightly too tight to fit comfortably inside the Jeffries bellows:

bellowsmould3

I could have tried to unglue the blocks and glue them onto new plywood strips with the correct spacing, but I decided it was easier just to start again and remake them all. By the end, I was getting really tired of the noise the milling machine made as it cut the valleys, not to mention the dust everywhere!

I made the core of the bellows mould by mitring the edges of six pine boards on the bandsaw and gluing them together. I deliberately made it slightly oversize, then hand planed it to final shape/size (a good idea as it turned out slightly wonky, plus I wasn’t certain exactly how big it needed to be until I tried assembling it inside the Jeffries bellows):

bellowsmould4

The stand is a simple affair with the vertical ends roughly dovetailed to the base. A nice feature of this style of core is that if you turn the central bar one way up, it presents the sides uppermost, and if you turn it the other way up, it presents the corners instead. This picture also demonstrates that the scrap Jeffries bellows fit on the mould:

bellowsmould5

Finally time to start making the bellows! I cut the 108 individual cards out by hand, using a template I cut from a piece of scrap aluminium to match the shape of a card taken from the Jeffries bellows:

bellowsmaking1

I hinged pairs of them together using strips of fine-woven linen cut on the bias and bookbinders’ maize paste (very similar to wheat starch paste but supplied pre-cooked and with some anti-fungal stuff mixed in):

bellowsmaking2

Then I hinged the pairs together into six strips. Note that the hinges are both on what will become the inside of the bellows, and the valley hinges have to be pasted on with the hinge partly closed or they will tend to tear themselves apart when they close. There may be a less fiddly way to do this but it seemed to work well enough.

bellowsmaking3

After the paste had initially dried, I noticed that the cards had all warped a bit, so I pressed them all tightly in a big wooden clamp for a couple of days (forgot to take a photo), which helped to flatten them out again.

I tied the strips of cards onto the mould with string, then hinged the corners together with more bias-cut linen, though at this point I switched to using hot rabbit-skin glue. It’s messier and more difficult to work with than paste, but in my tests it was the strongest of all the glues I tried (slightly stronger even than PVA wood glue, and significantly more flexible when dry).

bellowsmaking4

I made a simple press to clamp the bellows shut, and whenever I had to let the glue dry before the next stage, I took the bellows off the mould and transferred them to the press. If I hadn’t, they would have dried in the fully-open position and possibly torn apart when I tried to force them closed. It’s also necessary to periodically take the bellows out of the press and exercise them to avoid them drying fully shut.

bellowsmaking5

Next I glued on the valley leather strips. I used goatskin for all the leather on the bellows. I pared the valleys down to about 0.65mm and skived the edges for cosmetic reasons. They are simple rectangles rather than butterflies because that’s how they were on the Jeffries bellows I was copying:

bellowsmaking6

Next the gussets:

bellowsmaking7

Here’s a video of me gluing a couple of gussets on:

The top and end runs. In hindsight the end runs would have worked better if they were both narrower and thinner, and perhaps I need to work on my technique for gluing them on, because I was unable to get them to go round the corners without creasing, which caused the end sets of gussets to be stiffer than the rest. It probably didn’t help that I made the cards all the same size (the end ones probably should have been slightly taller because of the inset):

bellowsmaking8

Pressing it all together:

bellowsmaking9

To make them look a bit prettier, I made bellows papers from decoupage paper:

bellowsmaking10

I screwed a plain piece of plywood onto the bottom end, with a sheet of black “funky foam” (closed cell EVA foam sold in thin sheets for craft purposes) as a gasket, and a couple of pieces of scrap lead to pull the bellows open with a consistent amount of force:

bellowsmaking11

The top board has a reed holder next to one edge. It’s a simple design that doesn’t require any adjustment for different sizes of reed, though you do have to hold the reed in place with your thumb while sounding it. The top plate is slightly thinner than a reed frame so that it’s possible to file the reed in situ, and it has a slight undercut so as to hold the dovetailed reed frame more securely. It took some careful measurements and fiddling about to get the wind slot just right so that it works for the full range of sizes of reed I had available. It might require further adjustment if I ever want to use it with even bigger reeds from a bass instrument. The separate brass screw is used in conjunction with a specially shaped thin spring-steel shim (not pictured) to hold the reed tongue up above the frame while filing.

bellowsmaking12

Here’s the finished tuning bellows clamped to my bench. The flap of leather is a relief valve to let the air out when you raise the bellows. Not clearly visible in the picture, there are a pair of straps tacked to the sides of the frames that prevent the bellows opening too far.

bellowsmaking13

Finally, here is a quick video of me showing them in action. The reeds are the highest and lowest reeds from my antique Lachenal 48-button English, plus the A4, which is at 444Hz because it is tuned in old pitch, meantone temperament.

I want to thank Geoffrey Crabb for all his advice on the construction of the bellows moulds and the tuning rig, and also Bob Tedrow for his bellows-making essay (although my technique is quite different, I picked up several good ideas from it).

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