Steppers

The stepper motors have arrived that I’m going to use to convert my Taig Micro-Mill to CNC.

steppers

It’s hard to explain how exciting this is. I’ve dreamed of owning a CNC machine tool for probably twenty years and yet somehow never got around to building one. I bought the Taig about a decade ago for another project with the intention of fitting it with DC motors and encoders and building my own servo controllers (in hindsight that was a bit of a silly idea considering steppers are relatively cheap and work OK on a machine as small as the Taig). I got as far as buying the motors, encoders, pulleys and toothed belts, and a large block of aluminium that I was going to machine the mountings from, before the project ground to a halt. There are some photos on my old website of the mill when I first received it. I have used it occasionally as a manual mill but what I really want is to be able to use it to machine complicated parts under automatic control.

The motors are bigger than I expected, and I went for the small end of the range people tend to put on this machine. There are a couple of different theories on stepper motor sizing for the Taig mill: 1. use small motors and keep everything well adjusted and lubricated so you don’t need lots of torque. 2. use big motors so you have lots of torque in reserve and it doesn’t matter so much if the leadscrews and slides get a bit stiff. The advantage of the smaller motor option, as well as lower cost (both in terms of the motors and the electronics to drive them), weight, power consumption, and heat generated, is that smaller motors have lower winding inductance and armature mass. Lower inductance means the torque doesn’t drop off as rapidly as the speed increases; lower mass means they can accelerate and decelerate quicker. I’ve read people advocating both paths and claiming to get better results with small/large stepper motors, but the smaller, nimbler option appealed to my sensibilities more (as somebody who is happy driving a small, light car with a 48Bhp engine).

 

 

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Swanky Switch

I’ve spent what seems like an inordinate amount of time getting the bellpush switch right. This photo shows my first attempt:

switch1

The long contact strip is made from a roughly T shaped strip of 0.7mm brass. It’s bent into a zig-zag at one end to make it more flexible (I also had to file it narrower for the same reason). One of the problems I ran into was I initially didn’t recess the contacts deep enough to ensure the terminal screws can’t press against the underside of the top. The top of the flexible strip is slightly curved so that when the lip of the button pushes down on it, it flexes a little and ‘wipes’ the contacts against each other to (in theory) break through any oxide film that may have developed since the last time it was used. The contacts are made of short sections of flattened 4mm diameter sterling silver rod (for good corrosion resistance), silver-soldered onto the brass parts. The screw terminals are salvaged from a UK 13A mains plug, filed a bit narrower due to the limited space available. I did all the soldering with the Eclipse spirit blowpipe described in an earlier article. They are held down by M2.5 stainless steel machine screws, mated to square S.S. nuts morticed into the back of the box.

When I got to this stage I thought the switch was done. The button action felt nice and the contacts closed when I pressed it. Unfortunately there was a problem, as I discovered when I proudly showed it off to my friend Juliet. She pressed it normally a couple of times and it worked fine, then she tried pressing it really gently. It didn’t work. She tried the same thing a few more times with intermittent results and proclaimed it faulty.

It was a user interface problem: press the button down firmly all the way to the bottom and it worked fine. Press it very gently and it was possible to feel the slight increase in resistance as the contacts began to close and stop pressing too soon. Result: the bell doesn’t sound, and you might not realise if you were outside and the bell was inside. I suppose some people seeing such an ornate bellpush might think that it looks delicate and press the button gently in fear of damaging it (in fact you’ve probably got more chance of breaking your finger than the button). This graph illustrates the problem (figures are estimates):

buttonfeel

The problem is that first step when the button lip touched the flexible contact strip and the switch began to close. If you were pressing gently enough, it (wrongly) felt like that was the bottom of the button travel when you actually needed to press a tiny bit harder to close the contacts.

I won’t go through the list of ways I tried to solve this problem. I now have quite a collection of discarded springs! What I eventually settled on was a second helical torsion spring attached to the top of the flexible contact that applies gradually increasing pressure to it over the  full length of the button travel. The result is that the switch closes smoothly without any detectable step increase in force, and the contacts are fully closed at about 80% of full travel. If you press the button firmly enough, it bottoms out against the top of the contact strip and wipes the contacts as originally intended.

I also had to remake the first spring with more and bigger coils to weaken it (I could also have used thinner wire but I didn’t have any in stock), because the combination of the two springs made the button force uncomfortably high. I didn’t want to remove the first spring and just use the second one to return the button because it’s set such that the pressure on it is zero at the top of the button travel so as to ensure the contacts release properly, which means the button wouldn’t return to the top as cleanly with that spring alone.

Here’s a cute picture of the little bracket I made to attach the new spring. I filed it from one of the brass 13A plug pins that I got the screw terminals from and silver-soldered it onto the contact end of the flexible strip (that’s a 0.8mm diameter hole):

switch2

This photo shows the final setup. The brass peg to the left of the flexible contact (a screw with the head filed down) is there to ensure the torsion spring can’t swing to the left and disengage from under the button:

switch3

 

Now that I had a working bellpush, I wanted to make a little video to show it off. I don’t have an electric bell here and the continuity buzzer in my multimeter doesn’t sound impressive enough, so I hooked it up to something else instead:

 

 

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Clico Swiss Bench Shear

Here’s another lovely vintage tool; one that almost certainly will get used in my concertina production. It’s a small Swiss-made bench shear of a design that I have never seen before. One of the blades is a helical shape (that must have been pretty tricky to make!), and as you rotate it the shearing point slides along the fixed straight blade. The maker’s stamp appears to say ‘Clico’ but other than that I know very little about it. It’s quite small and very precisely made; I suspect it was probably intended for jewellery or clockmaking. It was a little bit pricey for a second hand tool (about the same as a new Chinese-made bench shear of more conventional design), but it’s such a lovely thing and works so well that I regard it as a bargain. As long as I don’t abuse it and hone the edges occasionally, it should outlast me. When I got it the blades were quite blunt but it still cut surprisingly well. I sharpened them last night and it now cuts really cleanly with more control and much less effort than a pair of hand shears.

shear1

The state the edges were in before sharpening:

shear2

The unclear maker’s stamp. I think it says “Clico”. The number doesn’t seem to refer to a patent (too short). Perhaps it is a serial number.

shear3

 

A brief video showing how it works (I would normally use two hands but one was holding the camera):

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Moore & Wright Spirit Blowpipe

I love old well-made tools. Recently I picked up a vintage Moore & Wright spirit blowpipe (I thought they only made measuring tools!). It’s a very nicely made brass wick burner with a pipe that allows you to blow a stream of air across the flame. This creates a very hot, concentrated flame that can be used for hard soldering. I may not actually use it in concertina production (I have several modern gas torches than are more convenient and powerful), but I thought readers might be interested to see it.

blowpipe1

blowpipe2

I haven’t quite got the hang of it yet; it’s much trickier to use than a gas torch. It also doesn’t seem to produce much heat. I suspect it would work much better on a jeweller’s charcoal soldering block because then any excess oxygen in the stream would make the charcoal burn and generate extra heat. I tried it with a piece of ordinary barbecue charcoal but it crackled and spat sparks at my face so I quickly gave up! I also suspect the meths I’m using may be too dilute to produce a really hot flame.

Here’s a video of me experimenting with it. As you can see the brass got hot enough to anneal it but I doubt it was hot enough for silver soldering.

Update: I spent a while this afternoon practising with the blowpipe and successfully made several silver-soldered brass joints on the refractory brick in the video above. The key seems to be to blow very lightly and consistently (using circular breathing technique) in subdued lighting so you can see the parts of the flame clearly, and at all costs don’t let the blue inner cone dwell on the work. It is far colder than the outer flame. It also helped to push out a bit more wick to get a slightly larger flame. The job took longer than it would have with a cheap butane gas pencil torch, but I got there in the end.

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Crafty Concertinas

I’m in the early stages of designing a logo for Holden Concertinas that will also be used as the maker’s label on my instruments, and I mentioned to a friend that I was considering including the phrase “Hand crafted in England.” I intended that phrase to put across concepts like small production quantities, hand assembly, care and attention to detail, tradition, built by an individual who really cares about the end product. In other words the opposite of “Mass produced on an assembly line in China.” My friend pointed out that hand crafted may be a controversial claim to make because I am intending to use CNC machine tools to produce some of the parts for my concertinas. I wondered whether I would be safe if I dropped the word hand, e.g. “Crafted with Care in England” or similar, though I’m uncertain if that is any better (and it doesn’t sound as good to my ear).

Since then I’ve been thinking about what the word craft and the term hand crafted mean to me and reading other opinions on the subject. I came across an interesting essay this morning about the ongoing debate over the meaning of the marketing term craft whisky (apparently there is such a thing – I had never heard of it) that made me question whether I can use the term craft at all when I am only just starting out in the business of musical instrument making. After all I certainly wouldn’t dare to call myself a master craftsman at such an early stage in the development of my new career, though neither would I say that I am completely inexperienced or lacking in craft skills (including the use of traditional hand tools).

In the case of my concertina-making operation I will be assembling all the parts and tuning and finishing the instruments by hand. A fair amount of skill will be required and little or no use of power tools, so I think this part of the process certainly ought to count as hand craft.

What about the parts that I will be assembling? Most of the screws and the action rivets I will probably buy ready-made because they are so generic that there would be little point to making them myself. The rest of the parts I intend to make in my own workshop, with the possible exception of laser-cut metal end plates (a machine powerful enough to do that kind of work is far outside my budget). The raw materials I’ll be making the parts from will be things like seasoned hardwood, brass sheet, spring steel strip, various kinds of tanned leather, card stock, wool felt, hide glue, shellac. That is to say, pretty much the same types of raw material that traditional concertina makers like Wheatstone and Lachenal used back in Victorian times (though I don’t intend to use bone, ivory or endangered woods, and may also use make some use of more modern materials and adhesives when appropriate). The tools I will be using to make the parts can be divided into four categories:

  1. Hand-powered tools that require a significant amount of manual skill to operate. Things like files, hand saws, hand planes, chisels, skiving knives. Many would include treadle-powered machines like my scroll saw in this category because they are also propelled solely by the muscles of the operator (incidentally, Geoffrey Crabb told me that his reed pan routing machine that was made by his great grandfather in the 1860s was originally treadle powered). Purists would argue that this is the only category of tool you can use if you want to describe your product as hand crafted. In some cases (e.g. chainsaw carving) I might even agree with them! 😉
  2. Externally-powered (typically by an electric motor) machine tools that require a significant amount of manual skill to operate. This includes things like manually controlled lathes and milling machines, drill presses, bench grinders, as well as woodworking machines like bandsaws and table saws, planer/thicknessers and drum sanders, even sewing machines. Non-purists will usually allow items made with this type of tool to still be called hand crafted – after all a skilled pair of hands was still required to twiddle the knobs or push the material through the machine in just the right way. It is an area of considerable debate, particularly in cases where the end result is indistinguishable from an item made entirely with hand tools.
  3. Hand-powered tools that require little skill to operate. This is mainly things like punch and die sets used in hand presses. You stick a piece of raw material into the tool, pull the handle, clunk, briefly inspect the part that pops out, and place it in a box if it looks satisfactory. Repeat the operation over and over until you have replenished your stockpile of that part. Anybody could be shown how to do it in five minutes. Personally I would describe parts made this way as hand made but possibly not hand crafted due to the lack of skill required. Obviously the design and manufacture of the die sets is another matter – that does require skill, and I intend to perform that part of the process myself too. Does that elevate the parts I’ll be making this way to the status of hand crafted? I don’t know.
  4. CNC machine tools. I intend to make extensive use of small CNC machine tools including a lathe, a wood cutting router, a milling machine, probably a laser cutter (though in that case I’ll have to send my designs out to a commercial machine shop), and possibly a surface grinder for profiling reed tongues (which I may need to build myself because commercial ones are rare, expensive and larger than I need). Wire EDM is also worth considering, specifically for cutting the reed frame slots. The main reason I’m planning to use CNC where it’s practical to do so is to reduce the amount of time I spend doing highly-repetitive machining operations that a robot can do faster and more consistently without getting tired or bored. I’m pretty sure this doesn’t count as hand crafted because there isn’t a human hand guiding or powering the tool as it cuts. Can it be called craft though? This brief article on the subject argues that it can. Considerable skill is certainly required to teach a machine to make a new part, and in many cases also to make jigs to hold the parts securely and accurately while they are being machined, but once that has been done you can pretty much load a piece of raw material into the machine, press ‘start’, and go off to do something else while it works its way through the list of instructions. Admittedly the kind of machine I’ll be able to afford will require a lot more manual tending (e.g. changing the tool bit part way through a job, or turning the workpiece over so that it can machine the other side) than the big machining centres used by commercial machine shops that can go all the way from bar stock to bucket of finished parts without human intervention. Most of my parts will also require some manual finishing-off, e.g. deburring edges, polishing (where externally visible), and tapping threads. The reeds in particular, arguably the most important parts in a concertina, will require a considerable amount of skilled hand work to finish them off after the components have been roughed to shape using the CNC milling machine (traditionally, this roughing out stage was usually done using punch and die sets in a fly press).

Enough rambling. I’d like to know what you think. Will my concertinas be crafted or merely made? Is it valid to describe them as hand crafted if some of the parts in them were machined by power tools and even robots?

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Bellpush Spring

Not much progress on the bellpush over the past week because most of my attention has been focussed on another non-concertina-related project. Yesterday was a day off though, so in the evening I managed to stop thinking about the other project for long enough to tackle the problem of the spring that provides the button resistance.

My original plan had been to use a single strip of brass as both the button spring and one of the switch conductors. This turned out to be impractical though because the button has a vertical travel of 5mm and there isn’t enough room inside the box (once you’ve allowed room for mounting screws and electrical screw terminals and things) for a really long spring strip. A short strip probably wouldn’t be able to flex by 5mm without permanently deforming and even if it could, it would likely result in fatigue failure before long. I experimented with folding a brass strip back and forth in a zig zag to increase its effective length, but it looked like it would take up far too much space and probably still wouldn’t work very well.

So the solution I eventually came up with was to separate the two functions. Make a concertina-style spring from coiled phosphor bronze wire with 5mm travel, and a separate brass strip switch that only has to move by 1mm or less at the bottom of the button travel. I haven’t yet made the switch but I have made the spring. It took me four attempts before I developed a shape I was happy with, using a hole in a block of scrap wood as a test rig. It has more turns than a standard concertina spring because of the large amount of movement relative to its length.

bellpush_spring_1

Here it is installed in a recess chiselled into the back box. It’s in a slightly weird location because of where I intend to put the mounting screws and switch contacts:

bellpush_spring_2

I won’t bother posting a photo with the top installed because it doesn’t look any different on the outside! The action feels pretty nice though.

 

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