Holden Concertinas – Page 10 – Bespoke High Quality Musical Instruments

Punching Washers and Grommets

Techniques, Toolmaking, Tools / October 16, 2016

I decided I wanted to try making some punch tooling in order to manufacture a couple of the parts involved in a traditional concertina action: the felt washers that go under the buttons and the leather grommets that screw onto the ends of the action levers.

As well as the big Smart & Brown 2-ton toggle press mentioned previously, I also have a little 600N Brauer one (if my calculations are correct, the big one is rated to deliver about 30 times the force of the little one). I got it second hand some time ago, with some odd custom tooling attached to it that I never figured out what it was supposed to do. Here it is after removing the tooling and cleaning it up a little (yes, that is an old gear knob on the end of the handle – actually quite a nice addition so I left it on):

Because the throat height of the press is considerably more than the thickness of a piece of felt or leather, I turned up a 50mm tall spacer block from scrap 1″ mild steel bar. It bolts to the table of the press and has an M8 threaded hole in the top for the punch anvil, and a cross hole for the ejection of waste punched through the hole in the middle of the anvil.

I needed to cleanly bore out the inside of the felt washer punch, so I ground a simple D bit from the 1/4″ shank of a broken HSS end mill:

I drilled most of the waste out first, then used the D bit to open it out to 1/4″ and cut a flat bottom on the hole. At this stage I also drilled a 1.5mm hole for the centre pin:

I used the compound slide to turn the tapered sections of the top punches, stopping while the edge was still fairly blunt. After hardening and tempering, I put them back in the lathe and used emery paper to clean up the taper and sharpen the edge.

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

The anvil and felt washer punch installed in the press. I made the half-nuts that are used to lock the tool at the desired height by facing ordinary full nuts on an arbor.

Here’s a quick video clip showing the felt washer punch in use:

This shows where the washers go on the buttons, to stop them making a clacking noise when they bottom out:

A nice stockpile of washers for my first few instruments. I made these from a sample piece of ‘baize’ woven wool cloth as used on gaming tables. I also have several other sample pieces in various different colours. I think the original washers may have been made from an actual fine, thin felt rather than a woven cloth, though – I need to get hold of some samples to experiment with.

The first anvil I made had a design flaw: the hole through the middle for the ejection of waste material was drilled 1.5mm diameter all the way through the tool. In practise it quickly became constipated and I had to repeatedly remove it and drill out the waste. The one on the right is a second, improved version that is relieved to a larger diameter until a couple of mm from the top surface:

Here are all the punches and anvils I made. The first one is the felt washer punch. Inside it is a couple of layers of spongy foam and then a couple of felt washers; with careful adjustment of the pressing force this seems to be just right to prevent the washers getting stuck inside. The second one I had optimistically hoped might work the same way, but the grommets just got stuck inside it and wouldn’t come out, so I instead decided to use it to punch out the centre hole and mark the location of the outside of the grommet, then switch to the third punch which has a slot milled in the side to allow the grommets to be pushed through and removed from the top.

Here is a video clip showing the leather grommet punches in use. Note that in the video I was using 2.5mm veg tan cowskin, however I subsequently found that I got much better results from 4mm leather instead (the 2.5mm leather compressed down to 1.5mm in the punching process and the 4mm to about 3.2mm). I also removed the stripper plate seen in the video because I found it was getting in the way and causing more trouble than it was worth:

This shows where the leather grommets go inside the instrument. They screw onto the end of the lever arm (which is lightly threaded), then glue to the samper disc on top of the pad:

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

Although these are fairly trivial parts, it certainly feels like progress to be stockpiling significant quantities of production-quality parts that I have made using my own tooling.

UPDATE: I’ve since got hold of some 0.8mm piano bushing cloth and punched more washers from it:

The piano bushing cloth is thinner, finer, and more tightly woven than the baize. Unfortunately I’ve only been able to find it in bright red with a white core. I may experiment with dyeing some of it black.

Website News

Website / October 16, 2016

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.

Reed Tongue Shear

Reeds, Toolmaking / September 29, 2016

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!).

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.

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

Reeds, Techniques, Tools / August 3, 2016

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!