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.


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.


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.


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:


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


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.



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


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


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:


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.


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).


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:


My first brass reed in the instrument:


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!


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):


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


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


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:


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:


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:


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:


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):


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:


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:



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:


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.




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.


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:


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:


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


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:


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


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:


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


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:


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):


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:


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:


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):


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.


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).


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.


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:


Next the gussets:


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):


Pressing it all together:


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


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:


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.


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.


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).


Hand-Cut Maker’s Mark Punch

There is something magical about the ability to anneal1 high-carbon steel, work it into a useful tool, then harden and temper it so that it can hold a sharp cutting edge for a long time. It was one of the most important discoveries of the Iron Age, enabling the manufacture of tools that were far superior to those made of softer metals like copper, bronze and wrought iron.

I have made a few hardened steel tools of my own; wood carving knives and gouges, and simple punches. It is a wonderful and exciting feeling to use a tool that you made yourself.

Part of the process of hardening tool-steel involves heating it to something in the region of 760-800C2 and holding it at that temperature for a while. If the temperature is too low the steel won’t harden properly, and if it’s much too high you get a coarse grain forming inside the metal that will affect your ability to sharpen the tool. In the past I’ve heated my tools using either an open solid-fuel forge or a propane blowtorch, but in both cases it is difficult to accurately gauge and regulate the temperature. Because I need to make more tools for concertina production (mainly press dies), I’ve been looking out for a better way to heat them.

Recently I came across an old electric laboratory muffle furnace on eBay. Luckily I managed to get it very cheaply because it was described as faulty and it was near enough for me to collect it in person. It looked to be in good condition in the photos, and I figured that even if the heating element had burned out, it would be cheaper and easier to re-wind it than to build one from scratch.


The fault turned out to be very simple. It is supposed to have a fusible link inside the inner chamber that melts if you overheat it (a thermal fuse). This was probably quite easy to do because the original controller was a simple simmerstat3, and I suspect leaving it at 100% would cause it to reach melting point in about 45 minutes. The thermal fuse was missing. As a temporary measure I bypassed it and the oven fired straight up.


I learned nearly everything I know about heat-treatment of steel from Hardening, Tempering & Heat Treatment by Tubal Cain from the Model Engineer’s Workshop Practice series. It was only after I’d bought my oven that I happened to be flicking through the book and saw a picture of it: the author had the same model!

Tubal Cain had replaced the simmerstat in his heat treatment oven with an early computerised temperature controller. I wanted to do the same thing, and I could have simply bought a fairly cheap Chinese PID controller like the one I used on my glue pot (though high-temperature ones seem a bit harder to find and more expensive), but for various reasons I decided to build my own instead. I used a MAX31855 thermocouple interface from Adafruit, an Arduino Nano clone, a solid state relay, a 16×2 alphanumeric LCD (HD44780 compatible), a couple of push buttons and a rotary encoder stuffed into a plastic project box. Because I already had most of the parts other than the high-temperature K-type thermocouple (which I would have had to buy anyway) and the MAX31855, the project worked out pretty cheap.


I developed the firmware using the Arduino IDE and several off-the-shelf open source libraries. This is the first time I’ve used the Arduino system, though I’ve done quite a bit of embedded programming in the past. I must admit a decent C++ compiler and a large set of libraries made it pretty easy to quickly bolt something together, though the lack of a debugger is a bit of a pain, and some of the libraries are poorly documented and/or provided with example code that doesn’t work properly out of the box.

The most difficult part of the project turned out to be tuning the PID loop parameters. Get them wrong and the oven either never reaches the desired setpoint or it overshoots and oscillates around the setpoint. One advantage of developing my own Arduino-based controller was that it was easy to log the temperatures and power level at regular intervals to a laptop over USB, then plot a graph to figure out what was happening over time. To cut a long story short, after hours of test cycles and trying many different values, I eventually found a set of parameters that perform well enough for my purposes. It overshoots by a few degrees when it first gets up to temperature or after disturbing the system by opening the door, but I don’t believe that is enough to cause a problem. In this graph, the blip at 5200 seconds is the result of me opening the door for a few seconds:


For years I have been fascinated by how punches and dies were made prior to the invention of the rotary engraving machine. I’ve read what I’ve been able to find on the subject (not very much, to be honest) and studied some antique punches to try to work out how they were made. I decided to try making a punch from my maker’s mark to see if my ideas were practical.

I think positive punches and single-line name stamps usually used at least one counterpunch per letter to form the hollow spaces (the counters), and the outside waste was cut away with saws, files and probably a selection of gravers. There were also negative punches that were probably either entirely engraved or stamped with a set of reversed positive punches, but I’m not going to cover those today.

My maker’s mark is a fairly simple symbol (an upper case A with two arms added), though I wanted to challenge myself by making a serif version with multiple stroke widths.

I made both the counterpunch and the punch from 3/8″ silver steel, which is a commonly-available high-carbon water-quenched tool steel with a little chromium in it that is supplied as accurately ground round bar. Since the counterpunch was to be smaller than the punch I first tapered the end. There are several ways to do this, but I decided to use the compound slide on my Taig lathe. I also used the lathe to face both ends to make them square, and used a file to round over the hammer ends a little so that when you strike it you don’t hit a corner.


The facing process left the end that was to become the punch square and reasonably flat but very slightly rough. Because this might effect the performance of the finished punch I decided to lap it flat.


First I clamped the blank in a Vee block, using a piece of paper as a shim to make sure the punch protruded from the block by a tiny amount:


Then I lapped it on a cheap diamond plate in a figure-eight pattern:


The lapped face of the punch blank:


Next I started cutting the counterpunch using a jeweller’s saw to make the initial grooves:


I removed the waste from the outside using a fine flat hand file:

Then I used a graver to widen the grooves (you can see in this one it’s pretty small compared to my index finger):


The nearly-finished counterpunch:


To check it was the right shape, I got it sooty in a candle flame and pressed it onto a piece of paper (this is called a smoke proof). Actually I realised at this stage that I had made a mistake, but I opted to push ahead and modify the proportions of the punch to compensate rather than starting again. I could get away with this because the design of my mark is rather fluid anyway, and doesn’t have to match the style of a particular font.



The final part of cutting the counterpunch was to bevel the corners and do a test punch into a piece of end-grain hardwood. I’ve found that a punch doesn’t work very well if you don’t bevel it at all, but it’s not entirely clear to me how steep the bevel angle should be (the old punches I’ve looked at aren’t all the same).


Next I had to harden the counterpunch before I could use it. In order to reduce scale buildup and decarburising while soaking in the heat treat oven, I coat the business end of the tool in jeweller’s borax flux. Applying it isn’t an exact science. I warm the punch to not-quite boiling point, then smear some thick borax paste onto it and wait for it to dry. Once in the oven, it will bubble up a bit at first but then it should melt and flow out across the surface (you can see the difference after heat-treating; the areas that were protected by the flux are still bright underneath).


I put the counterpunch into the oven on top of a piece of bent stainless steel that prevents it directly touching the oven floor. After waiting something like 20 minutes for it to get up to temperature, I let it soak for another 20 to ensure that it was fully austenized all the way through. From what I’ve read, not soaking for long enough will significantly reduce the hardness you can achieve.

After soaking, I pulled it out with blacksmith’s tongs and immediately quenched it in a bucket of water. The shock actually causes most of the Borax flux to fall off, which is handy because it can be difficult to remove.


As a quick check to make sure it hardened, I see if a file will cut it. Generally it will scratch a tiny bit because of the surface decarburisation effect but it will be hard enough underneath that the file just skates off. Some people recommend using a good sharp file for this test, but I find that it tends to blunt the file so I prefer using a rubbish file and just press quite hard (I have experienced a tool that didn’t harden properly and the difference was pretty obvious).

After hardening, the steel is very hard but also very brittle and highly stressed. If you’re not careful you can shatter it just by rough handling (I’ve done that with a fancy spring clip that I had just spent half an hour forging). What we do to cure this is to temper it, which means re-heating it to a lower temperature and soaking it for a while. This reduces the hardness somewhat but also reduces the internal stress and greatly increases the toughness of the steel. If you temper it lightly you end up with quite a hard tool that might be at risk of chipping. Higher tempering yields a tougher but softer tool; if you go too far the edge may tend to roll over in use. The highest levels of tempering are used to make springs.

There are several ways to heat a tool for tempering. I could even use the heat treat oven itself, but it would take a few hours to cool down sufficiently and it’s not a good idea to leave the tool in its fully hard state for that long. I decided to use a small electric deep fat fryer with sunflower oil in it. The highest temperature the thermostat will go up to is about 200C (and the oil probably wouldn’t be happy going much higher than that), which is towards the low end for tempering silver steel.


After tempering I used a rotary wire brush in the pillar drill to remove the scale and any remaining flux.


Finally I used a spirit burner to re-heat the blunt end up to a spring temper so that it can better resist the shock of hitting it with a hammer. It will probably mushroom eventually but it is easy to cure that by grinding. After it reached a blue colour I quenched it again to stop the heat travelling too far up the shank.


A quick test in a piece of scrap aluminium proved it had worked as planned:


The first stage of cutting the real punch was to strike the counterpunch into it. I think this is possibly the most difficult part of the entire process. You have to line it up perfectly, then hit it multiple times very hard to drive it as deeply as possible into the steel. Although the silver steel is supplied annealed, it is still a pretty tough material and it takes a lot of force to counterpunch it. The counterpunch bounces out of the indentations after every strike and you have to be very careful to line it back up perfectly before the next strike – I had a bit of an accident and made an extra small dent but luckily it was in a waste area. The counterpunching causes the surface to raise up a bit around each indentation, which I opted to get rid of by lapping it flat again. Here is the result after counterpunching and lapping:


I roughly removed the majority of the waste from the outside with a jeweller’s saw and files again:


Mostly done, though not yet adjusted the width of the strokes:


After a bit more fine fettling, and adding the bevels:


I didn’t bother photographing the hardening process as it was exactly the same as for the counterpunch. The final set of photos shows the result of testing it in several different materials. First end-grain beech:


Aluminium, both a light strike and a heavy one:


A light strike into side-grain pine tended to crush the soft fibres:


End-grain pine worked fairly well though. The bottom one was an experiment in soot blackening the punch first:


Brass. I had to hit it pretty hard to get a decent impression but it came out quite nicely:


Thick leather. This looks sharper in reality than the photo appears to show:

Mild steel. The top mark was a moderately hard strike onto the wooden bench and it’s barely visible. The bottom mark was a very hard strike backed by a steel anvil. I’m not sure I’d want to risk striking the punch that hard very often as I’m concerned the tiny serifs might be at risk of breaking off, though it didn’t suffer any visible damage as a result.



Small Roubo-inspired Pine Workbench

I’ve just finished building a new workbench for my concertina-making workshop. bench1

I designed it myself, loosely based on an 18th century French design described by Andre Roubo. Although mine is much smaller, made from construction-grade pine, and has modern (ish: they are probably older than I am) cast iron quick release vices instead of a wooden leg vice, they do have several important elements in common. The joinery is very similar, particularly the unusual dovetailed tenons that allow the legs to come flush with the edge of the top. It has a planing stop, a front vice, a holdfast, and a tool tray between the stretchers.

I made it 1m tall, which is on the high side for workbenches, because I mostly do fine detail work on small components, often under magnification, and in these circumstances a high bench reduces back ache from constantly bending over. The top is 400mm deep by about 1.2m long, which I felt was the biggest I could comfortably fit in my small garden shed workshop while also fitting in a coal stove to the left of the bench and two machine tool stands along the back wall.

The next few pictures show a few of the many workholding options available to me on this bench. The Woden quick-release front vice with leather-lined jaws is likely to be my main workhorse:workholding1

I also have a very similar Record quick-release vice, which I installed as a central tail vice with leather-lined wooden jaws that span the full width of the end of the bench. This idea is a bit of an experiment on my part, but I have a feeling it is going to come in handy (obviously I will have to be careful to avoid clamping things too far off-centre as excessive racking force could damage the vice).workholding2

For light metalwork, I welded up a steel bracket that allows me to hold a Record No. 3 in the jaws of one of the woodworking vices (I’ve since painted the bracket the same colour as the vices):workholding3

The holdfast is an important feature of Roubo’s workbench. Instead of the traditional forged iron bar that wedges into a hole when you hit it with a mallet, I went for a Woden hold-down clamp that performs pretty much the same function but with a screw to control the clamping force. It fits into a special tall cast iron collar with ridges inside that mate with notches on the back of the vertical rod, and it only came with one collar, so I put a lot of thought into the most versatile place for it to go on the bench.

Another important feature of Roubo’s bench is the adjustable-height planing stop. Mine is a significantly different design, though it performs the same function. I made it from a limewood board without any metal teeth on the top, partly to avoid marring the work but mainly because I don’t want to risk accidentally running into it and damaging the plane, particularly when planing very thin stock. There is a wing nut under the bench that allows it to be clamped at the desired height.workholding5

A feature of Roubo’s bench that I didn’t copy is the crochet; the hook on the front that you would use to wedge the end of a long board when jointing. It didn’t really make any sense given the fact that I can’t easily remove my front vice, which in any case can easily be used to clamp the end of a long board.

I also have various clamps and small vices that can be held in the bigger vices to hold things in creative ways:workholding7



I don’t yet have any bench hooks or shooting boards, though I plan to make some soon.

The idea of the tool tray under the bench isn’t permanent storage, it’s just somewhere convenient to put down tools that you aren’t currently using, other than putting them on the bench top itself where they get in the way and risk being knocked onto the floor. I modified the idea a bit though, by putting mine on hinges with a storage box underneath it:bench2

My plan is to store heavy things in here, thus lowering the bench’s centre of gravity and making it more stable. Currently it contains five fire bricks (!), a bunch of metal clamps, and a couple of small anvils. Combined with the fact that the bench structure itself is very rigid, the two other things I did to stop the bench moving around in use were that I glued rubber pads to the bottom of each leg and I attached the tops of the legs to the wall of the shed with angle-iron brackets, after bolting a steel channel to the wall to make it more rigid. I’m very pleased by how well this has worked.

Light is extremely important for fine detail work of the sort found in concertinas. Of course I put the bench next to the window to pick up what natural light I can, but that isn’t much use when it’s dark outside! The ceiling is too low for a conventional fluorescent light tube above the bench, and spotlights are problematic because they cast light and dark areas. After a bit of research I found out about LED light panels. I bought a 300 x 1200mm 40W daylight panel and fitted it directly above the bench, and I was amazed by the quality of light it produces. It is like being directly under a skylight on a bright day.ledpanel(On the negative side, I also replaced the bulbs in the two batten light fittings with newfangled LED filament bulbs, and I found those to be a bit disappointing: slightly dimmer than the claimed equivalent tungsten bulb, with a very dim patch directly below the bulb).

To finish up, here is a selection of pictures from the construction process.

The wood I bought to construct the bench, mainly 3″ x 3″ planed “redwood” (i.e. Scandinavian pine). IIRC it cost about £40 including the T&G on the left that I used for the bottom of the tool box (the lid was a piece of scrap plywood I had lying around).benchbuild1

First I had to restore my Record No. 7 jointer plane, which I had never really had a use for before now, not being a furniture-maker.benchbuild2


Then I used it to joint the boards that I glued together to form the long stretchers and the top:benchbuild4

I glued one joint at a time using hot hide glue and three sash cramps (it might have been preferable to use a couple more, but I was horrified when I found out how much decent ones cost). My vintage electric iron was used to preheat the wood to extend the glue’s open time.benchbuild5

After the top was fully glued up, I roughly trued and squared it with a wooden jack plane:benchbuild6

Then I flattened the top surface with the jointer plane. After final assembly I re-flattened it, and was surprised to discover that in the intervening couple of weeks it had cupped by about 2mm.benchbuild7

Cutting the joinery:benchbuild8







First assembly of the bench, with Pippin the pushme-pullyou dog (this was an accidental trick photo caused by my dad activating the panorama feature on my iPhone).benchbuild15

All three vices needed a good cleanup and repaint. The Woden vice also turned out to have had the quick release mechanism modified in an inexplicable way that prevented it functioning – after reversing the bodge it worked fine.

Annoyingly the new paint didn’t dry very well at all, and after several days I got fed up waiting for it to harden and fitted them anyway, resulting in the very soft paint rubbing off in a few areas.

Making riven beech pegs to hold the joints together. I didn’t use any glue, or even bother to drawbore them.benchbuild18

Setting the hold-down collar into the benchtop using my router plane.

The fixed jaw of the end vice was morticed into the benchtop to avoid having a gap between the end of the bench and the wooden jaw.benchbuild20

Unlike the Record vice, the Woden one had a really rather wonky top surface where it bolts to the underside of the bench.
benchbuild21As a result, I had to spend a couple of hours painstakingly carving the underside of the bench to match the top of the vice in order to get it to fit snugly and not rock:

Before I finally attached the top to the legs, I whittled my maker’s mark and the year of construction on the underside:benchbuild23

The long stretchers were held into the legs with both a peg and a pair of wedges (which open the tenon out into a deliberately tapered mortice). This is a very strong joint, even without glue. Getting the wedges out if I ever want to disassemble it will probably be a bit of a struggle though.benchbuild24

Simply screwing the hold-down collar to the bench top didn’t work very well; when I tightened the clamp the screws started to pull out, so I fixed the problem by making this steel clamp plate that goes on the underside of the bench. The screws are M5, stainless steel.benchbuild25

The short section of benchtop behind the planing stop shrunk and split after a few days, so I cut it out and scarfed in a chunk of dry oak instead.benchbuild26


New Beginnings

I have moved back to Burnley! Soon I should be able to start making progress on building my first instrument. Currently my tools and materials are piled up in crates and boxes in my bedroom and garage, and my milling machine is broken down into several pieces, so my first task is to convert this damp 6×8 feet garden shed into a cosy little workshop:


At some point I hope to save up enough money to replace it with something a bit bigger and more substantial that is designed from the ground up to be dry, insulated and secure. For now, my plan is to install a tiny coal stove (which can later be transferred to the new workshop), repaint the outside walls, add more ventilation, and store as little as possible in there when I’m not actively using it.

The first thing I intend to make in the new shop is a workbench. Nothing massive or fancy, just a solid pine worktop (made from a spare kitchen table I found in my parents’ loft) at a convenient height, secured to the floor/wall, with some old cast iron vices and a planing stop. After years of working on flimsy trestle tables and Black and Decker Workmates, it will be great to have a sturdy fixed bench that doesn’t skitter across the floor when I try to plane something. In a stroke of good luck, just as I was starting to think about workbench design, I happened to stumble across a copy of The Workbench Book by Scott Landis for a couple of pounds in a local charity shop. It’s a hefty book filled with inspiring ideas. My first self-built workbench probably won’t be my last, but seeing what other woodworkers are working on has helped me to identify more clearly what features I think I will find most useful for the type of work I do and avoid some things I might have regretted later (e.g. I don’t want any dog holes in the top: too easy to drop small parts down them).

Making concertinas from scratch requires a lot of tools. Metalworking, woodworking, leatherwork, and some very specialised things like a tuning rig. In addition, there are opportunities to speed up production if you invest in special tooling and machines. In order to try to avoid falling into the trap of Tool Acquisition Syndrome (gotta collect them all!), I’ve started categorising tools like this before I decide whether I need to buy one or not:

  1. Tool that is the bare-minimum cheapest way to perform an essential operation. For example, it’s perfectly possible to cut out fretwork ends using a cheap and cheerful bent steel fretsaw you can pick up for a quid or two at most car boot sales. I have a few of these in various sizes. They are a bit slow and tiring to use for long periods, but they are perfectly capable of producing excellent results.
  2. Tool that speeds up an essential operation. For example, a scroll saw is a machine that does essentially the same job as a fretsaw but can cut perhaps four times as fast with less physical effort. The difference is actually probably less significant with more complex designs because you spend so much of your time stopping and moving the blade to a new piercing. I have both a treadle and an electric scroll saw. I should probably get rid of one of them to save space, but I need to do some proper side-by-side tests before deciding which of them I prefer to use.
  3. Tool that is a higher quality version of something I already have. For example, my scroll saws are both hobby-grade machines: either will do the job for now, but certain features are inaccurate, fiddly and annoying to use, or not built to last. If in the future I find myself with the budget to upgrade, it would be nice to step up to a higher quality saw like a Hegner, or maybe even a vintage industrial machine.
  4. Tool that would be nice to have, but isn’t essential to concertina-making at all. I’m struggling a bit to continue with the fretwork analogy here. Let’s say an electric bandsaw: one could perhaps argue that it could be used to rough out the blank more quickly than with a handsaw, but it isn’t of any use for cutting the fretwork itself because you can’t get the blade inside a closed piercing (and they can’t cut very fine details and tight curves).

Milled Boxes

It has become a tradition for me to make several Christmas presents each year using whatever tools/skills I have picked up most recently. This year my latest tool acquisition is the CNC milling machine, so I decided to do a project that would show off some of what it can do, as well as giving me some useful experience in programming it. A friend suggested trinket boxes. After considering various possible construction methods, I settled on milling them from blocks of limewood with thin plywood bases and lids.

I needed to make presents for three people. The nature of one-off CNC manufacture is such that most of your time is spent at the CAD/CAM stage, because you have to plan every detail in advance and figure out how to tell the machine what to do (being careful to avoid anything that is physically impossible, for example asking it to cut a 3mm wide slot when your smallest cutter is 3.175mm in diameter). It would have been easy to design one box and produce three exact copies, but where would be the fun in that? I instead decided to do three different designs. I learned new things from each one and I feel the third design is the best, so it wasn’t a wasted effort.

The CAM workflow was basically the same as with the maker’s mark stamp except the designs and machining operations were far more complicated. An additional step was deriving the profiles of the lids from the shapes of the rebates they sit in; this was complicated slightly by the fact that I needed to round off all the points because the internal corners of the rebates can’t be any sharper than the diameter of the router bit.

The milling operations themselves mostly went OK. I suffered one stepper motor stall while milling the first box, but I heard it happen and managed to hit the e-stop in the nick of time before it did any noticeable damage.



I made one design mistake: one of the lids was cut to the wrong outline (you can see it in the next photo). I didn’t spot it at the simulation stage because it was approximately the right shape for the compartment, just slightly too big.


When I cut the replacement lid I took the opportunity to make a little Christmas tree decoration at the same time:


The boxes looked pretty plain with ordinary birch plywood lids, so I bought a selection of patterned decoupage paper on eBay and pasted various combinations to the lids. I also pasted plain coloured paper to the bottoms.


I turned the knobs by hand from beech. Because there was quite a bit of variation I made more than I needed and picked out sets that went well together.



Here are all three finished boxes after lacquering:


The ‘S’ box is my favourite (made for my mum, Sandra):


I came up with the basis for the design while playing around with mathematical knots. It is based on the 8 18 knot.

Incidentally I now have an Instagram account and I’m using it to post pictures of things I’m working on.