Turning End Bolts

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:

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:

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:

Slitting the head of the bolt. #cncmilling #taigmill #concertinamaker

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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.

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Brun Addendum

My use of a working title to describe my first instrument in the past few blog posts was causing a little confusion, so I have now chosen an official name for the model: the Holden Concertinas Brun.

The name comes from the River Brun, which most historians believe my home town is named after (Brun Ley over time became Burnley)1. The name of the river may have come from the Old English word Brún, which is an adjective meaning, “brown, dark, dusky; having metallic luster, shining.”2

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Brun Part 8: Conclusion

It has been a long and at times bumpy journey with a successful arrival at the end. I have produced a good quality, attractive, playable instrument, where I made every part myself except the reed clamp screws and end bolts. I have learned or improved many skills along the way: CNC, toolmaking, metalwork, woodwork, leatherwork, French polishing, tuning, and so on. Where I made mistakes along the way, I have learned from them, and I am certain #2 is going to be even better. The instrument is currently away being evaluated by an expert and I have already heard some encouraging feedback. Hopefully at some point I will be able to post links to reviews and videos of it being played.

What’s next? I am in the early stages of designing and tooling up to make a pair of new instruments, both of them fairly traditional 6 ¼” hexagonal Anglos, one with wooden ends and one with metal ends. A bit further down the road I have plans for a larger and more ambitious Hayden duet. I am also taking on more repair work: having made a complete instrument from scratch, I am now well-equipped to take on any aspect of fixing a traditional vintage instrument.

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Brun Part 7: Reed Pans

The seventh part of the story of how I built my first concertina is about the reed pans; the removable boards that carry the reeds and valves.

One thing I have learned is that the reed pan layout is one of the most difficult and important aspects of designing a new instrument from scratch, and it has to be done in conjunction with the action board layout. It’s no good coming up with a nice logical arrangement of chambers on the reed pans, if it means some of the pad holes end up underneath the keyboard, or the levers have to snake around all over the place to reach the appropriate pads, or you have to use levers that are too short to operate smoothly. Sometimes you have to compromise in one area or another, either in the reed pan (e.g. making reeds smaller because there isn’t room for the ideal size of chambers), or in the action (e.g. making two levers cross over each other or bend sideways).

This being my first instrument and a brand new design, I spent several days at the design stage figuring out a good compromise. When I began the process, I wasn’t even sure how many buttons I was going to end up with (the design brief specified the overall size of the instrument, to include as many buttons as practical in that form factor). The design I came up with looks pretty simple and logical, however in order to reach it, I tried and discarded a number of more complex arrangements. The three main compromises I ended up making were that a few of the levers are shorter than ideal (those buttons feel a bit stiffer than their longer neighbours); six of the chambers are in the centre of the instrument (for reasons I don’t fully understand, they sound a bit less good than chambers on the outside – this is a well-known phenomena in the concertina world); and I was forced to abandon the idea of including an air button.

You might find it interesting to take another look at the photos of Wheatstone’s Duett concertina of the 1850s. My Brun is the same size but with an extra three buttons per side. To achieve that, I went with a similar reed pan arrangement but with a second, smaller pan on each side. Wheatstone’s had one pan with two rows of six chambers; mine has a pan with two rows of five and a second pan with one row of five. Five columns is actually a fairly tight fit in the available width. I tried fitting in six and it was ridiculously tight: I suspect Wheatstone must have used narrower reed frames and smaller diameter pads, which probably had a negative effect on the sound it produced. My actions are a more conventional riveted lever type, and I suspect are probably more comfortable to play.

My first idea for making the reed pans was to mill them from thick pieces of birch plywood. This didn’t really work, because the chamber dividing walls were too weak due to the cross-grain layers, causing them to break during the machining process.

Plan B was to mill them from solid quartersawn sycamore. Using quartersawn wood means it will move and warp less due to changes in humidity level. The little bandsaw I had at the time was just barely powerful enough to rip the slab I had in the thin dimension.

Looking at the end grain, you can see it is reasonably quartersawn towards the bark side of the piece. Because the pans only needed to be a little over 4″ wide, I was able to pick the best section.

Planing one face true.

The bandsaw was never going to resaw the full width of the board, so I had to do it by hand. Step 1 was to make a kerfing saw; a special tool that cuts a shallow kerf at a specific distance from the face of the board.

This kerf was then used to help guide the path of an ordinary rip saw.

Here are the two roughly sawn reed pan blanks, with the rip saw I used behind them. I’ve since got a bigger rip saw with coarser teeth that would have made the job a bit easier, but it wasn’t too bad really because the boards are so small.

At this point I put the blanks on one side and started recording their weight once a day. Although this slab was supposedly kiln dried before I bought it, it still seemed to have a higher than equilibrium moisture content inside. They lost a few grammes of moisture each over the first few days, and warped a little too. After a couple of weeks they stopped losing weight, so I felt they were probably stable enough to carry on working on them. First I planed one face of each flat and smooth (this face was to become the bottom of the pan) and ripped them narrower, being careful to follow the direction of the grain as closely as possible.

I left the other face alone because I planned to use the milling machine to flatten it, thus getting it very accurately parallel.

Problem! When I mounted the blank on the milling machine, the back edge fouled on the bottom of the Z axis slide before it was far enough back for the cutter to reach the front of the board.

The solution was to make a thinner fixture that (just) allowed the blank to fit under the Z slide. The two small holes in the middle of either end match with registration pins in the spoilboard, thus allowing the blank to be flipped over and still be in the same position, so the bottom reed slots end up in the right place relative to their chambers.

Oops. I did something stupid in zeroing the Z axis and plunged the 1/2″ end mill a few mm deep into the first blank. This could have been a major setback as I didn’t have a spare blank prepared, but luckily I managed to reposition the pan on the blank such that the damage was in an area that was due to be milled out anyway.

After truing up the top surface, I flipped the piece over and cut the bottom slots. There needed to be little pockets next to each dovetail slot for the dovetail cutter to start in, because the tool isn’t designed to be able to plunge into the work. I cut the wind slots for the bottom reeds at the same time as the dovetail slots, to ensure they are perfectly aligned with each other.

Bottom reed slots cut.

Back to the top again. I cut the outsides of the pans before the chambers, but not all the way through the board, because this reduced the amount of stress on the dividing walls. This picture shows how I managed to position my previous accident inside a region that was due to be removed.

Both reed pans fully routed. The left hand one is off-centre because of the previously mentioned repositioning.

This picture shows a few interesting things. In order to fit the reeds in as tightly as possible, the frames overlap, but not quite enough for a dovetail slot to break into the opposite side’s wind slot. They also undercut the walls slightly, more so at the outside edge (because the frames are tapered). Thirdly, I tried something new here that I haven’t heard of any other maker doing in this way: I made the chambers different depths, based on a ratio of the chamber length. It was common for English concertinas to have sloping pans, where the chambers at one end were deeper than at the other, but that only really works when it’s possible to arrange the pan in such a way that the pitches gradually increase from one end to the other. The way I did it here, it was possible to have a deep chamber right next to a shallow one (the first and second chambers are an octave apart).

The inner walls of the bellows frame are tapered to get a good seal, so I had to cut a matching taper on the outsides of the reed pans. The side walls I was able to do on the shooting board with a shim to tilt it up.

I daren’t try to use the shooting board to plane across the ends of the chamber walls, so I used the linisher for that instead.

Checking the angle with a bevel gauge.

It took a fair bit of careful work to get a good fit because the earlier problems with the frames not gluing together perfectly square meant the holes the reed pans had to fit into weren’t quite square either. In hindsight it might have been easier if I’d fit the pans to the frames before I put the chamois leather gaskets on the frames, and it definitely would have been much easier to do it before attaching the bellows to the frames.

If you’re familiar with more conventional concertina reed pans, you’re probably wondering at this point how you pull out the reed pan (which tends to be a fairly tight fit) without a hole in the middle to put your fingers through. Because I didn’t have any space for the finger hole, particularly on the left hand side, I instead attached captive nut plates on the bottoms of the larger pans and made a leather handle that screws onto the pan.

Once you have lifted out the larger pan, you can put your fingers through the hole and push out the small pan from underneath.

Here’s a quick video clip showing the first time the instrument made a sound:

Without the action boxes, every note plays at once. #concertinamaker

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When I made the bellows frames I didn’t know how deep the reed pans were going to be, so I allowed a generous depth of 20mm and put off the decision until later. As it happens, I eventually made the left hand pan 18mm deep and the right hand pan 16.5mm, which meant I then had to add some sort of spacer blocks that stopped the pans going in too deep. I thought I could just make strips that went all the way around, but they fouled on the bottom reed clamps so I had to cut a lot of notches out of them. In hindsight I went about this a particularly difficult and tedious way, and on future instruments I will be reverting to the traditional-style corner blocks instead, preferably fitting them to the frames before the bellows!

Gluing strips of chamois leather to the tops of the walls with rabbit skin glue. I found that skiving the ends of these strips needs a slightly different technique to skiving bellows leather because the chamois is so soft and stretchy.

All the gaskets installed.

I made the valve restraint pins from chrome plated sewing pins. After struggling to push a few of them through the chamber walls with needle nose pliers, I found they went in a bit easier if I sharpened them on a stone first.

There’s a bit of a knack to deciding exactly where to place the pins, so as to allow the valve to open properly without getting stuck. On my next one I’m planning to try making the pins from a slightly smaller diameter stainless steel spring wire instead.

I had lots of problems with the valves. My first attempt, I cut them by hand from sheepskin skiver, and they were terrible. The leather was too stiff, and every note sounded muffled if it played at all. My second attempt, I bought a set of valves from a parts supplier, and I’m not totally sure what the problem was but they didn’t seem to want to stay flat against the pans. This photo shows how some of them have lifted up until they are touching the restraint pins. This caused a problem with the bottom few notes making a sort of ‘raspberry’ noise if you changed bellows direction while holding the button down because the valves weren’t keen to stay closed.

On advice from several other makers, I ordered some hides of Columbia Pneumatic Leather from Columbia Organ Leathers (who are based in a town called Columbia, Pennsylvania, not the Republic of Columbia). It’s not cheap but it’s nice stuff. I removed all the previous valves (I found the easiest way was to just rip them off, then use hot water to remove the remnants of the old glue) and cut a new set, mostly from the extra heavy weight hide, though I did use the heavy weight for the higher notes. It was recommended to me to wash the leather and dry it on a sheet of glass to make it a bit stiffer, but I couldn’t tell any difference before and after washing (maybe I did it wrong). For the most part, the new valves behaved much better and solved the problems I was having. A few of them misbehaved in testing, not always for obvious reasons, but replacing them solved the problem.

Here’s one of the misbehaving valves where I was able to find the cause. If I played the blow reed, then played the corresponding suck reed very softly, it would start muffled, then ‘pop’ and play normally.

It turned out I had glued it off-centre, and one edge of the valve was getting sucked down into the wind slot.

Replacing it in the correct position solved the problem. It’s quite tricky to get them positioned right because you can’t see the slot while you are gluing the valve down. I’ve considered drawing a centre line in pencil first.

The finished reed pans. Note all the marks in biro indicating where and which way round they fit.

These two pictures show the difference in size between the biggest chamber (C3) and the smallest (G5). In hindsight I suspect I could have made them all a bit smaller, but I was trying to be conservative and working on the theory that a too-small chamber will sound terrible, whereas a too-big one will just start up slowly. In fact, as far as I can tell, they all seem to respond pretty quickly.

The final thing remaining was fine tuning all the reeds, and bits and pieces of troubleshooting: tweaking the action to eliminate ciphers, replacing misbehaving valves, etc. The client asked me to tune the reeds in quarter comma meantone, with G as the root note. I made a quick video clip showing it playing a few chords, though in hindsight this doesn’t really show it off very well. You’ll have to take my word for it that it has a much nicer sound in person than recorded on an iPhone microphone. I hope at some point I’ll get to hear what it sounds like in the hands of a good player.

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