Prototype Action Lever

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

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:


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):


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.


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:


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:


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.


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


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.


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:


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.


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:


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.


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:


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


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:


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.

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.


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


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.


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.