I have recently completed my second Blackbird Anglo concertina. It was a complete re-design with some fairly significant improvements over the prototype model.
A few weeks ago, a fellow concertina restorer contacted me to ask if I might be interested in manufacturing reproduction Wheatstone-style nickel-silver-capped buttons. As it happened, I had already been planning to develop the tooling to make this style of button for use on my own instruments.
I used solid acetal (Delrin) buttons on my own first instrument. They work fine and I expect them to last a long time if not abused, but I can’t deny that they have a ‘cheaper’ feel than metal, that isn’t really in keeping with the materials used for the rest of the instrument. As the maker, I know each button was lovingly hand-turned and polished, but a layperson could assume they were squirted out of a machine by the million like toothpaste tube caps.
Historically, cheaper instruments had bone buttons, whereas high-end instruments usually had nickel-silver (German silver) buttons. Solid nickel-silver buttons are surprisingly heavy, so manufacturers typically either drilled a hole in them and soldered a thin cap over the hole, or pressed a cap from thin sheet metal and used it to cover a lightweight core made from wood. Wheatstone later switched to making the cores from plastic because it is less prone to splitting.
My collaborator sent me a sample vintage Wheatstone button, and I started reading about press tool design. It was the first time I’ve made this sort of tool and possibly my most ambitious toolmaking challenge to date, so it took me a little while and I made a few mistakes along the way.
I did nearly all of the toolmaking on my little Taig micro lathe; it’s a surprisingly capable machine if you keep your tools sharp and stick to very light cuts.
I made the blanking punch from an 18mm silver steel bar, and the die from an O1 steel plate with a 1″ thick mild steel guide block bolted over it.
Boring out the guide block on the Taig lathe; this was a bit scary swinging such a heavy lump of steel at the lowest speed the lathe can manage:
Then I unbolted the guide block without moving the bottom plate from the chuck, and bored the hole in the die slightly larger to give the appropriate clearance between the punch and die.
Brass spacers guide the nickel silver strip through the tool.
Shearing off a strip of 0.5mm nickel silver to feed into the blanking punch.
The blanking punch produces 18mm discs. I drive it with a sharp whack with a lump hammer rather than using the press, both because it’s quicker and because a sudden shock will tend to shear the metal cleaner with less distortion than slowly pressing the punch through it.
The next tool was the cupping die, so-called because it turns the flat discs into cups. The bottom die has a recess bored into it to hold the disc perfectly centred over the hole.
After putting the disc into the die, I clamp the guide plate over it (light finger pressure is sufficient), then drive a polished silver steel punch with rounded corners down through the die with my arbor press.
This produces shallow, large-diameter cups. They are already starting to look a little bit like buttons if you squint.
Next I need to take the cups through a series of redrawing stages; each one reduces the diameter of the cup by around 20% while also increasing its depth. If you tried to go straight from a flat disc to a finished button cap in one stage, the walls would wrinkle and jam in the tool because there’s a limit to how much you can alter the shape of the part in each pass. The square parts in this photo are a mild steel tool holder, then there’s the silver steel punch, die, and guide, with an acetal spacer between the two. I later figured out that this stage works more reliably if I clamp it together very lightly with spring washers, so it’s possible for the guide to lift slightly if it has to.
The first redrawing die is a reverse die; this means you place the cup over it and the punch turns it inside out. In hindsight this probably wasn’t the best idea, but it does work. I did it because it looked easier to make, and I wasn’t aware of the drawbacks involved in reverse redrawing.
The cup comes out of the bottom of the die stuck on the end of the punch. Sometimes they can be very tight and difficult to remove. An industrial drawing press has something called a ‘stripper’ that holds onto the part while the press yanks the punch back up through the die with a lot of force, but with my low-tech tools I have to resort to manually knocking them off using a bar with a hole in it.
The rest of the redrawing dies are direct dies; i.e. you place the cup into a large section at the top of the die, then the punch forces the cup through a narrower neck with a rounded corner at the top.
Pushing the punch through the die with my Jones & Shipman arbor press. I was a little concerned before starting the project that it might not prove strong enough for the task, but in fact it is quite capable of bursting open the top of the cup if it gets stuck in the die.
A successful second redrawing.
The two diameters inside the top of the die need reaming with a purpose-made D-bit. By making a single tool that reams both diameters at once, it was also able to form the rounded transition at the top of the neck (this is a very important feature of the die because the metal won’t flow smoothly around a sharp corner).
The inside of the final redrawing die, after reaming with the above tool. Of course I also had to polish it smooth after hardening it to keep the friction as low as possible. You can’t see it in this picture, but the neck is quite short, with a slightly larger diameter section below it.
I found it wasn’t necessary to clamp the guide block down on the last redrawing tool:
Here’s the full sequence of parts produced by the above stages. The blank disc is 18mm diameter, and the final cap is about 5.8mm diameter by 15mm deep:
I encountered quite a few problems along the way; in particular I found that the parts often jammed in the die and burst because the bottom edge of the cup had become thickened. In theory you can work around that by increasing the clearance between the punch and the die, but I found that caused other problems, so before the second and third redrawings I instead manually grind a little bit of thickness off the lip of the cup, just enough to allow it to go smoothly through the die.
I found that I got better results if I annealed the cups between stages. It probably isn’t strictly necessary to anneal every time, but it did seem to help them draw more smoothly with less force. In my initial experiments I annealed them with a blowtorch, which works OK but takes a while and uses a lot of gas if you’re making lots of them.
I next tried putting them in my electric heat treatment oven.
This did a nice consistent job of annealing them, but because they were exposed to the oxygen in the oven for a long time, they built up quite a lot of scale that caused so much extra friction inside the die that I had to spend ages polishing it off before they would redraw smoothly.
Next I tried putting them in the electric oven inside a tin with a little hole in the lid.
The buttons were coated with grease used to lubricate the drawing process; as this burnt off, it displaced the oxygen inside the tin and generated a little flame at the vent hole:
Much better. They came out of the tin a little sooty and discoloured, but nice and soft with no significant scale buildup. I cooked them at 450°C for an hour, which is probably overkill but didn’t do any harm. I will experiment with reducing the time when I do the next batch.
After the final redrawing stage, the caps were approximately the right diameter but a bit lumpy and too long. To cure this, first I mounted each cap on a tapered wooden mandrel on the lathe and used a wide flat fine file to smooth them out:
A quick polish brought out a nice shine:
I made a special soft collet to hold the buttons bottom-out in the lathe while I parted them to length. Incidentally, those random frilly edges are very typical of drawn sheet metal parts and are called ‘ears’.
There is a depth stop inside the collet, so I was able to lock the lathe carriage in place and quickly part off all the caps to the same length.
With the metal caps finished, I now needed to make the acetal cores. They are almost identical to the solid acetal buttons I made for the first instrument, apart from not bothering to give them a nicely-domed head or polish them.
1. Extend an appropriate length of ¼” black acetal from a collet.
2. Face off (only necessary on the first button from a new piece of stock).
3. Turn down to the right diameter to fit inside a cap. This is trickier than you might think because the acetal is very bendy and wants to deflect away from the cutting tool, particularly at the end furthest from the collet. It helps to use a razor sharp tool and cut to the final diameter in a single pass at quite a slow feed rate. Even so I had to experiment quite a bit before I was reliably producing cores that fit nicely.
4. Roughly round over the corner with a file. This doesn’t need to be pretty because it won’t be seen, but it is needed to allow the core to go all the way into the cap, because the inside of the cap is slightly rounded.
5. Part off to roughly the right length.
6. Put the core in another specially-made collet with a depth stop in it, with the bottom end facing out.
7. Face to exact length. Note that I have the carriage stop set to allow me to repeatably turn up to the transition between the pin and the main body of the core, so for this stage I clamp a spacer between the stop and the carriage that is the same thickness as the length of the pin.
8. Turn the pin to diameter in one pass. If you look closely you will see I ground a flat on the corner of the lathe tool in order to form a fillet at the root of the pin; this greatly reduces the likelihood of the pin breaking off if the button gets knocked hard.
9. Chamfer the point of the pin with a file.
Next we have to drill the cross hole and countersink both sides. The original Wheatstone core had a 2.5mm hole, but I find that 3mm holes work better with modern 0.85mm bushing cloth. To avoid needing to spot each hole with a centre drill, I instead got a 3mm twist drill and ground it as short as possible to make it very rigid so it doesn’t deflect and drill the hole off-centre.
This is the same fixture I used to hold the buttons I made for my first instrument, but I have modified it a bit and I’m now doing both the drilling and countersinking on my CNC milling machine instead of the manual drill press. Firstly because the mill is more rigid and accurate, secondly because it has a quick change toolholder that lets me swap between tools and know the tip of the tool will be the same distance from the spindle nose each time, and thirdly because I was able to write three very simple macros that repeatably perform exactly the same operations each time without relying on manual depth stops.
The pins in the mounting board correspond with the holes in the fixture and allow me to turn the button 180° to countersink the opposite side of the hole. The fixture is actually inaccurate by about 0.3mm, but because the error is the same every time I was able to program the machine to compensate for it and get the second countersink to line up pretty much perfectly (this wasn’t the case with the manual drill press, leading to the countersinks all turning out a tiny bit misaligned; probably not enough to significantly effect the operation of the action but enough to annoy the perfectionist in me!).
The countersinking bit. It has a 10mm shank and all my quick change toolholders are imperial sizes, so I had to turn a special adapter sleeve to avoid having to hold it in the drill chuck, which would have caused problems with the tool Z offset changing every time I swapped back and forth between the drill and the countersink.
A finished button core. With a little polishing, this would be perfectly acceptable as a solid acetal button.
I made a special tool to crimp the caps onto the cores. The Wheatstone sample had a single small dot, presumably made by something like a centre punch, but in my experiments I found that if I instead made a punch with a slightly blunt chisel-shaped tip, it takes several times the amount of force to pry the caps off.
A quick final polish on the buffing wheel:
Followed by buffing with a soft cloth to remove the polish residue:
Here is one of my buttons next to the Wheatstone sample. The main difference is the increase in the diameter of the cross hole:
And here is my full first batch of buttons (I would have made more but I ran out of materials):
Here is the full lineup of tooling I made for this process:
This has proved to be quite a challenging project at times, and as always there are things I would make slightly differently if I knew then what I know now, but I am very pleased with the high quality of the resulting buttons and I’m looking forward to building an instrument that includes them.
Some future experiments:
- Materials. I’m pretty sure this tooling would work with other non-ferrous metals. I have read that a fairly high percentage of the population is sensitive to nickel and might not be able to comfortably use an instrument with nickel-silver buttons. Alternatives include copper, various alloys of brass/bronze (some of which are more tarnish-resistant than others), or a silver alloy like sterling silver or Argentium. Aluminium could work but may be a bit soft and prone to oxidation. Titanium would be interesting but I’ve not yet worked with it and don’t know much about how easy it is to press. I’m not sure how well the tooling would cope with stainless steel, as it’s much harder.
- Diameter. English-made concertina buttons have been made in a variety of sizes between about 4.5mm and 6.5mm (German-made ones were sometimes even larger). Preferred diameter comes down to each player’s fingers and playing style, though there are practical limitations too (e.g. there may not be room in a very dense action for large-diameter buttons). The most common size for English-system instruments seems to have been 3/16″, or about 4.75mm. I don’t think it’s a coincidence that the cores of the buttons I’ve just made are also approximately 3/16″, which gives a cap diameter of about 5.7mm. It would be interesting in the future to try making another final redrawing tool that produces 3/16″ caps, and possibly yet another one to produce 1/4″ (6.35mm) caps.
- Tip shape. Another aspect of button design is the shape of the tip. From discussing this with players, it seems that some prefer very flat-topped buttons, others very rounded, and yet others are happy with a compromise somewhere in-between, with a very slightly convex top and more rounded corners, as in the caps I have just made. I think it would be fairly easy to make the caps more rounded by making a new final punch with the same diameter but a hemispherical tip. Making caps with a flatter top would be slightly trickier, because if the punch is too flat it causes a concentration of force at the corner which tends to burst the cap in the die. The answer might be to make the caps slightly rounded as above, then use a different tool that compresses the cap between a flat punch and a flat anvil (or perhaps the punch might even need to be slightly concave). More experimentation required.
- Length. Not exactly an experiment, but just to point out that because I’m turning the cores manually and the caps come out of the press several mm longer than necessary, it would be trivial for me to make buttons that are up to about 4mm longer or shorter for different depths of action box/thickness of end plate, or for a player who prefers buttons that are extra long or extra short. I can also alter parameters like the length and diameter of the pin and the location of the cross hole if necessary.
I recently fully-restored a 40-button Lachenal Anglo. It was in pretty poor condition when I received it. The wooden ends were non-original, damaged, and not very well made.
The bellows may have been original, but they were worn-out and patched.
There was significant damage to the woodwork, including a couple of split reed chamber walls.
The pads were mostly dust held together with blobs of sealing wax, and the springs were mostly non-original and much too strong, probably in a vain attempt to make the knackered pads seal.
Step 1: remove the old bellows.
The bellows frames weren’t too bad underneath, apart from a few loose/missing corner blocks.
Next I dismantled the actions, laying the levers out on a piece of card so I could figure out which was which when it came time to reassemble the instrument. Quite a few of the action box walls had come apart at the glue joints, but the wood wasn’t too damaged.
Most of the end bolts and corresponding nut plates were worn out, probably due to somebody over-tightening them in an attempt to make the instrument airtight (unsuccessfully, because the various boards had all warped).
I already wrote an earlier blog post about making the new end bolts. I also made and fitted a new set of nut plates from thicker brass (3mm rather than 2mm), so they will hopefully be less prone to stripping in the future. The new wood screws are stainless steel and slightly longer than the originals. I plugged up the old screw holes with matchsticks before fitting the new screws.
The end bolt holes in the action box walls were worn oversized (particularly at the tops, where the screw heads had sunk through the end plates and worn a deep gouge), so I plugged them all with beech dowels.
I glued the walls back together in a band clamp using hot hide glue. Unfortunately the top and bottom halves didn’t quite match up perfectly, which I later realised must be because they originally came from different instruments (they are a different wood, and the pad gouges on the inside of the top walls don’t marry up with the positions of the pads).
I used a simple jig to re-drill the end bolt holes a consistent distance from the outside of the instrument.
Then I clamped the bellows frame to the bottom half of the action box and drilled the tapping holes in the nut plates.
Once I’d got a couple of them drilled, I used spare drill bits to keep them aligned to each other while I drilled the other four.
I took the plates off again to tap them, to avoid embedding a lot of greasy swarf inside the bellows frames for perpetuity.
As I mentioned previously, two of the reed chamber walls had split. I could have attempted to glue them back together but I doubt it would have held up for long, so I unglued them (hot water to soften the hide glue, and waggling until it suddenly came free like a loose tooth).
I glued new quartersawn sycamore walls in place, with hide glue again, using the reed as a wedge to hold it in place while the glue dried.
One reason why this wall was weak was that part of it needs to be cut away to make space for the valve in the next-door chamber. I thought it best to chisel this out in-situ.
I used a combination of needle file and skew chisel to undercut the new wall for the dovetailed reed slots.
Both the action boards were badly warped, so they didn’t seal properly to the tops of the reed pan walls. I cured this by painstakingly lapping them using a sheet of sandpaper glued to glass. I don’t seem to have a picture of it, but I also inlaid a piece of sycamore to repair the deep gouge visible in this one where the sound post screw goes through it.
On the right hand reed pan, it was so hollow near the sound post screw hole that I decided to glue a piece of veneer to the area to build up the thickness before lapping most of it away. This incidentally also filled in the oversized gouge around the screw hole.
The reed pans were warped too, though sadly not in a way that matched the warping of the action boards, so I also had to lap the tops of the walls. To avoid removing too much depth from the chambers, I had to glue tapered shims to the tops of about half of the walls near the outer edge.
After getting the tops of the reed pans flat, I replaced all the support blocks in the bellows frames. This is far easier to do without the bellows in the way, hence why I did all the above work prior to making the new bellows.
This shows why you sometimes find a block or two that isn’t right in the corner of the bellows frame.
The woodwork repairs done, I made and fitted new chamois leather gaskets. Not pictured, it was necessary to fit card shims to the inside of the bellows frames before the chamois to get the pans to fit tightly.
I have recently bought an old picture framing mat board cutter. This tool makes it much easier to cut the bellows card into strips, bevel the top edges at 45°, and with a simple jig, cut the strips into individual cards. Incidentally I switched from 1.5mm thick greyboard to 1mm thick millboard. It is a little more flexible but the reduced thickness really makes the bellows feel a lot less bulky. I think it’s a better quality material too, and likely to last longer.
After my experiment with self-adhesive hinge linen on the last set of bellows, I went back to Fraynot linen cut on the bias, attached with a bookbinders’ starch paste. The resulting hinges are thinner and much more supple.
Because I originally made my bellows mould to fit a set of bellows that came off a 6″ instrument, and this was a 6 ¼” instrument, I had to pack them out a little using strips of thin plywood between the core and the forms.
This time I prepared all of the leather parts before starting to glue them on. I also refined the shape of the gussets a little, and skived most of the parts slightly thinner than on previous bellows.
The bellows immediately after taking them off the mould! They are initially quite stiff and need to be broken in. In order to maximise their useful range, I spent the next few weeks while I was working on other parts of the restoration alternating between squeezing them fully closed in my bellows press and stretching them fully open using a couple of the forms from the bellows mould, exercising them a bit every time I handled them. I think this treatment along with other improvements really helped; the finished bellows are the most supple I have made to date.
A set of reproduction Lachenal bellows papers really helped them to look the part.
I recently bought a small Eclipse fretsaw frame that is the ideal size for concertina ends; much less tiring to use than a standard large fretsaw frame. I had to make new blade clamps because the old ones had stripped threads. I made the new clamps from scraps of tool steel and hardened them, so they ought to last pretty much forever now! I also made a new saw table with a nice big flat rigid top.
This shows why I made the top of the saw table so high; I prefer to do piercing standing up, and this height results in my arms being in the most comfortable position.
I cut the new ends from 22 S.W.G nickel silver (German silver) sheet, starting by roughly cutting them out oversize with a slitting blade in an angle grinder.
The fretwork design is based on photos I found online of a vintage Lachenal 40-button, but I redrew it and modified it a little (eliminating the redundant unused button holes on the opposite side from the thumb button on each side).
I drilled all the holes first. The bolt holes are actually transferred from the action box frames, not the template. I later realised the button holes should have been a bit larger to give more clearance around the buttons, so I had to enlarge them after I had cut all the fretwork.
Piercing in progress. I actually find this one of my favourite parts of the job; my mind goes into a flow state, and when I emerge some hours later I have made a beautiful thing.
I’m going to skip over a few days of toolmaking here; I may come back later and write a separate post about it. I made a press tool modelled on the one used by the Crabb company, which crimps the edges of a metal end plate one side at a time.
The side on the left has been crimped, the tool is about to press the side in the middle:
The end result. I found I had to do some manual cleanup work to neaten it where it hadn’t worked perfectly, particularly in places where the piercings were quite close to the border.
I polished the finished ends using my Bridek polishing spindle and various Menzerna compounds.
The button peg holes in the action boards were both worn oversize, and probably no longer exactly aligned with the button holes in the new ends, so I decided to plug them all with beech dowels and re-drill them.
I made this tool to drill the button peg holes; the brass bush is the right size to slide in the button hole and guide the drill bit to the right location in the action board. I used the depth stop on my drilling machine to make sure I didn’t quite drill all the way through the board.
You can see in this one that the new holes are sometimes slightly off from where the old ones were; if I hadn’t re-drilled them, the buttons wouldn’t have lined up right, which would probably have caused them to stick.
In order to bush the button holes, I needed to screw a piece of plywood to the underside of the end plate so I could glue the bushes into that rather than trying to glue them directly to the thin metal. (I later cut the board to match the fretwork.)
A different special tool used to accurately locate the pilot holes in the bushing board.
I fitted loudspeaker grille cloth below the fretwork. It proved a bit tricky to get the button holes in the right places; I settled on making a card template, then placing the template over the fabric, cutting around it with a rotary cutter, and punching the holes through the card and fabric both.
I glued the fabric to the underside of the metal with PVA (rather a fiddly job to avoid baggy areas or holes not lining up). One side-effect of this was that the acidic fumes given off by the glue oxidised the polished surface of the metal, and of course I couldn’t just take them back to the polishing machine because it would probably damage the cloth. I managed to clean it off with dry jewellery polishing pads but it was a bit annoying. Perhaps epoxy would be a better choice.
I laser-printed a replacement maker’s logo on archival paper and stuck it on with PVA.
This is a taper reamer I made from silver steel to slightly taper the holes in the bushing boards. By making the holes looser at the bottom than the top, they are better able to cope with any slight misalignment than if the sides of the holes were parallel.
Similarly, I made a new bushing reamer that is continuously tapered, thus making the bushes looser at the bottom. You can also see in this picture that I cut the boards closely to the outline of the fretwork and coloured the edges black so you can’t see them under the grille cloth.
Lachenal action levers sometimes wear in a way that causes them to twist as they pivot, causing uneven movement and pads not seating properly. The way I fix this is by building up silver (hard) solder on the worn area of the lever, then filing it back until it fits well again. Usually the post isn’t badly worn enough to need the same treatment. I had to do this repair to about half a dozen of the levers on this instrument.
Cleaned and rebuilt actions, with new springs, bushes, dampers, pads, etc.:
My first attempt at the elongated air hole pad was to cut it from the same leather/felt/card sandwich as the ordinary pads. It sort of sealed, but would leak when you pressed the bellows hard. I worked out that it was because the card was too flexible; the ends of the pad were flexing up and letting air leak out. I fixed this problem by making a special pad with a top layer made from thin stainless steel sheet instead of card.
Skipping over a bunch of toolmaking again; I made a set of dies to punch my own valves to a consistent range of sizes. I also got hold of some special thicker (very expensive) leather that is better-suited for the largest valves. I made the new valve restraint pins from 24 S.W.G. stainless steel spring wire. I have switched to using gum arabic to glue the valves to the reed pans; it is plenty strong enough when dry, easy to use and non-messy, and very easily removed with a little warm water on a cotton bud when you need to replace a problematic valve. I lightly cleaned all the reeds, and where necessary shimmed the slots in the reed pan to get the reeds to fit snugly.
The strap-adjuster thumb screws were the wrong ones for the instrument; the thread didn’t fit the captive nuts. To cut a long story short, I decided to make all new nuts and screws with an M3 thread.
Luckily I was able to reuse the tiny wood screws; finding replacements for them might have been tricky.
I’m quite proud of these thumb screws; it may seem like a trivial detail but the first ones I made were pretty bad in comparison, and I really think I have got the hang of them now. If you dig back through my Instagram page, somewhere in there is a post describing my process.
There’s quite a bit going on in these next two pictures. Firstly, notice the bottom half of the wall is ebony (original to this instrument), the middle section is mahogany (probably came from a different vintage instrument), and then there’s what appears to be another ebony section between the mahogany and the metal plate. I needed to add the second black section as a spacer to make the boxes a bit deeper, because the action levers were hitting the bushing boards. It is made from a manufactured ebony substitute called Rocklite Ebano. Although I needed to do this for mechanical reasons, I actually think the three-layer effect looks quite unique and attractive.
Secondly, I sanded and lightly French-polished the woodwork. I deliberately didn’t go overboard building up a high gloss, and I tried not to remove too much of the old patina in the process.
Thirdly, I made new brass strap rings (the loop thing that holds the strap down to the thumb rest), replaced the captive nuts in the ends of the handles with M3 ones, and made domed brass washers to hold the fixed end of the straps.
Fourthly, I made new leather hand straps. I don’t think I’ve quite got the pattern perfect yet (the ‘tails’ are about an inch too long), but I have figured out how to round and smooth the edges using an edge beveler and a burnishing spindle so they feel more comfortable on the hands.
When I received the instrument it was in C#/G#, old philharmonic pitch, which is about half a semitone higher than modern concert pitch. In consultation with the client, we decided I would re-tune it up to D/A concert pitch. Actually, I later realised that it may have originally started out as D/A old pitch and been tuned down to C#/G#, because the note stamps on the frames made more sense if that was the case. Most of the reed tongues were steel but there were a handful of brass ones in there too; you have to be very gentle with them as a tiny amount of filing can cause a big shift in the pitch, much more so than with steel ones.
The highest reed on the instrument was missing. I worked out from button charts that it was supposed to be a very high F#. I made a replacement, making an educated guess as to the length of the vent. It was so small that I didn’t have an end mill that could cut the vent slot so I did it by hand with a jeweller’s saw and tiny files (not as difficult as it sounds, though a little time-consuming to get it perfect). After experimenting with the profiling for a while, I managed to get it sounding remarkably well on the tuning bellows. Unfortunately once in the instrument, this reed, along with the other three or four highest notes, were pretty unresponsive, needing quite a high bellows pressure to get them to start. After quite a long time spent experimenting with them, I came to the conclusion that the problems mostly came down to the reed chambers being too large.
The worst one would barely speak at all (the one on the bottom side of this chamber; it is quite a lot higher in pitch than the corresponding top-side reed). I managed to significantly improve it by replacing the end wall with one closer to the vent slot so as to reduce the chamber volume.
My highest reed was in an inboard chamber. I managed to improve its response by making a little removable block that significantly reduces the dead volume in the chamber.
The finishing touch was to add my mark to one of the reed pans.
I had one or two bits left over after I finished putting it back together!
The finished instrument (photo courtesy of the instrument’s owner, Wallace Calvert). I am particularly proud of how nicely the new end plates turned out.
And now for a special treat, here is a clip of Wallace playing The Humours of Tullycrine on the instrument:
On my first instrument, the ends were held on with commercially-made stainless steel allen-head M3 screws. They work fine, but I felt they gave the instrument a bit of a modern, almost industrial look.
I am currently working on restoring a vintage Lachenal Anglo for a client, and the end bolts and captive nuts are missing or badly worn due to past over-tightening (probably from trying to cure leaks that were actually due to internal structural problems). Needless to say, it wouldn’t have been appropriate to replace them with modern screws. Rather than try to source a better second hand set from a parts dealer, I decided it was time to figure out how to make my own new brass end bolts from scratch.
I sourced some 4.5mm diameter free-machining brass bar. The finished heads want to end up about 4.5mm, so I need to avoid turning it any smaller in the process. It came in 330mm lengths, which I figured out would comfortably make eight bolts if I cut it into four sections.
One bit ended up too short due to a mistake. Incidentally I used to think junior hacksaws were rubbish until I got some better quality Sheffield-made blades and found this excellent frame for a pound at a car boot sale. It tensions the blade really tight, which prevents it flexing in the cut, and the aluminium handle is really comfortable.
If I’d only been making a small number of them I probably would have held the blanks in the three jaw scroll chuck and accepted that they would turn out slightly non-concentric, but since I needed to make a large batch and will be making more in the future, I decided I wanted to use a collet instead. Taig (the manufacturer of my lathe) sells a few standard imperial-size collets, and blanks that you can drill to whatever size you want. I’ve had this lathe for probably fifteen years and this is the first time I have ever used one of the blank collets! They are made from a nice free-machining steel that drills very easily:
The difficult part is holding the awkwardly-shaped piece of metal while you cut the slots in it. I settled on putting a piece of the 4.5mm brass in it, and holding that in the vice instead of the collet.
Once I had sawn the first slot, I turned it 90° and used the slot in the brass bar to guide the saw while I cut the second slot. Then I flipped it over and cut the other two slots.
The finished collet. Not too bad for a junior hacksaw.
The first step in machining the bolts was to put the blank in the collet with enough protruding for a single bolt, then turn down the shaft to 2.25mm. Before doing the job, I spent a long time worrying about how I would do this without the shaft flexing away from the tool towards the end, resulting in it getting fatter towards the tip. This wasn’t as much of a problem as I expected it to be. Getting the tool bit really sharp and running the lathe at its maximum speed was a good starting point.
The first method I found was to turn the first third of the shaft to finished diameter a bit at a time, then move along and turn the second two thirds to finished diameter. This worked fine but took a couple of minutes per bolt. I found I could take heavier cuts on the second section, then I got to experimenting to see how far I could push it, and to cut a long story short, it turns out that it’s perfectly possible to turn the entire thing to finished diameter in one pass! Once I figured this out, it sped things up quite a lot. It’s important that you do it in one pass, because you need the full diameter of the bar to the left of the tool to support the cut. If you try to do a second cleanup pass, however light, the bar will flex at the end. Here’s a video clip to prove it:
Turning the shank of the end bolts. Before I made these I was worried about the material flexing and coming out tapered. Turns out there's an easy way around the problem: get the tool really sharp and go all the way down to the finished diameter (4.5 to 2.25mm) in one pass! Also having fun with my new tailstock die holder and a good quality used 8BA die. I'm turning the spindle in the second clip by pulling on the drive belt. #taiglathe #concertinamaker
Next I used a fine single-cut file to put a blunt point on the shaft.
Then I used a tailstock die-holder and a good quality sharp HSS die to cut the threads. I used a dab of cutting oil (it really makes a noticeable difference to how easily the die cuts) and turned the spindle by pulling on the drive belt, using a ruler to measure when the tailstock had moved far enough for the desired length of thread. The video above also shows the thread cutting operation.
A brief digression about the threads: the original Lachenal bolts are about 2.25mm major diameter, but a relatively coarse pitch. I haven’t been able to find any standard thread that matches it. Since I don’t have a screw-cutting lathe, to copy it I would have had to commission a specially made tap and die set, which would have been very expensive. I instead decided to use 8BA, which has the same diameter but a finer pitch. I don’t think this is a problem for the restoration because I am replacing all the bolts and captive nuts at the same time. From what I have read, the Crabb company used 8BA bolts in their instruments too. BA threads are mostly obsolete now apart from a few niche applications, but you can still get hold of new taps and dies for them.
After doing all the above steps to one end of the blank, I turned it around and did the same to the other end. I probably could have used slightly shorter blanks, it just worked out this way when I cut the bar stock into four.
Next I needed to cut the piece into two and form the domed heads. To do this efficiently I got a ¼” HSS tool blank and ground a special profile onto it. This profile first parts off the stock to length, then you carry on plunging it and it forms the domed shape.
Here’s a video of the process showing how quick it is:
Turning the domed bolt heads with a custom ground parting-off/form tool. I make the bolts in pairs, so this first operation splits them in two and shapes the head of the first one. I'll swap the other half into the chuck to put the head on that too. Later on I'll use a bit of hand held fine emery paper at the lathe's top speed to smooth out the shape a bit more. #taiglathe #metalwork #concertinamaker
Next I cut the slot in the head using a HSS slitting saw, 50mm diameter by 0.6mm thick with 100 teeth. I didn’t have a mandrel with the right centre diameter, but Taig sells blank mandrels that screw onto the headstock so you can turn a custom spigot to fit your saw blade. Luckily I have an older-model Taig milling machine that has the same headstock on it as my lathe; newer mills come with an ER16 collet chuck instead, which makes this sort of thing a bit more complicated because you can’t just transfer something straight from the lathe headstock to the mill.
A nice snug fit on the mandrel:
Next, I needed to make a special fixture to hold the bolts on the milling machine while cutting the head slot. I made the top part from aluminium, and the nut bar from mild steel. Tightening the set screw clamps the shaft of the bolt tightly.
The slitting setup on the milling machine:
Here’s a quick video clip of it cutting a slot:
Although I did it with a short hand-written CNC program because I have a CNC mill, this operation would be dead easy on a manual mill or even a milling attachment on the lathe. I found that with the CNC mill, I could load a bolt in, hit Start, go back to the lathe, turn the head on the next bolt, and return to the milling machine around the time it finished cutting the slot.
Next I put the bolt back in the lathe and used 800 grit emery paper and the top speed to smooth out any tool marks and burrs.
Finally to the polishing spindle to give the head a shiny finish. This Menzerna 480W compound is very effective on brass.
I had to use a screwdriver to clean excess polishing compound out of the slot of each one.
Here’s the first one I made between a couple of different ones from the vintage Lachenal. My head is more closely based on the shallower one on the right.
I made a batch of about seventy bolts; enough for the Lachenal restoration and my next few instruments.