Alex – Page 9 – Holden Concertinas

Prototype Action Lever

Techniques, Toolmaking, Tools / November 12, 2016

I made a prototype action lever. It’s a Wheatstone-style riveted lever hand-cut from 1mm thick brass sheet (the post is 1.5mm; possibly a bit thicker than necessary, but I didn’t want it to distort when I hammered it in).

The hardest part was making a die tool to thread the pad end so that I could screw the leather grommet onto it. Because the lever is cut from thin flat sheet rather than round bar, an ordinary thread cutting die wouldn’t have worked, so I instead made a sprung die set to form the thread.

I started with a 15mm x 25mm x 100mm bar of O1 tool steel, drilled and filed a spring shape on one end, then slit it in half:

Next I clamped it tightly together in a vice, and drilled and tapped an M2 hole in the middle of the slit, near the opposite end to the spring:

I put a couple of M5 threaded holes in the bottom so I could bolt it to a chunk of angle iron, then hardened and tempered it to 200C, differentially tempering the spring end to a higher temperature with a blowtorch so it won’t break in use:

After a bit of experimentation, I found that I could get it to form an acceptable thread if I cut a section of the 1mm sheet to 2.5mm wide (this dimension is fairly critical: 2mm forms almost no threads, and 3mm distorts and creases badly). It works best to hammer the tool fairly hard four times: once with the lever vertical, once each at 30 degrees from vertical in both directions, then a final time with the lever vertical again.

The lever after sawing it out with a jeweller’s saw, forming the thread, and riveting it to the post:

The proportions were based on one of the shortest levers in a treble English; most of the levers will have longer straight sections. The straight section is 2mm wide; I had to make the threaded part a bit wider (the tool squishes it narrower and thicker):

After screwing the grommet on. It is necessary to enlarge the hole in the leather grommet to 1.65mm before it will screw on without using excessive force and damaging the grommet:

Spring Winder

Techniques, Toolmaking, Tools / November 11, 2016

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

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.

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.

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

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:

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.

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

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

The finished spring:

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:

A few experiments with various arm lengths:

Prototype Pads

Techniques, Tools / November 10, 2016

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.

A pad ‘sandwich’ after gluing:

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.

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

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

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.

Bastari Repairs

Repairs / November 5, 2016

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.

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

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:

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.

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:

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

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):

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:

I sawed the new pivot pieces slightly wide, then carefully filed them down until they were a snug fit in the hole:

I glued the new pivot pieces in with Araldite Rapid Steel (an epoxy resin that is specifically formulated for gluing metal):

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.

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.

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.

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.

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:

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: