Arachne

A Story by David Hackett

  My string-winder has always been called Arachne – Google her if you don’t know the story.  It all started about twenty-five years ago, when I had just bought my first Broadwood square piano.  The piano needed a full set of strings, but I simply couldn’t afford to buy professionally made ones.  So I decided to make them, and thus Arachne was created.

  I had never seen a real string-winder (in fact, I still haven’t) – nor have I any idea where to buy one – so Arachne is purely the result of trial and error: plenty of error.  The long piece of oak which forms the bed, and the motor, are original, but other parts of the machine have undergone a number of developments.  This is the reason for the numerous battle-scars.

  This is Arachne in her current form, mounted on an old saw-horse:

  Version 1 was driven from one end.  Bad mistake!  The first modification was to add the long ‘layshaft’ to provide a drive to the tail as well as the head.  This is absolutely necessary, otherwise an unacceptable twist builds up in the core – and the swivel tail-bearing fails anyway. 

  Next joke: the layshaft as originally fitted had five equally-spaced lignum vitae bearings, plus the two ends.  The bearings are fine, but not the spacing!  The shaft quickly started to resonate at the sixth harmonic, and the whole contraption, workshop included, started to shake itself to pieces.  Easy solution: randomise the spacings (see pic. above).

  A word about speeds: Arachne’s driving force is the pump-motor from an old washing-machine.  I think it might run at 2450 rpm, but I’m really not sure.  Anyway, it’s much too fast.  Right from the start, I geared it down, but not enough: early rides were fast and furious.  Noisy, too, because I was using old Meccano straight-cut gears.  The current version uses two-stage toothed-belt reductions, which are real luxury. (Incidentally, the cost of these pulleys and belts were the first and only actual money that I have spent on Arachne – everything else was ‘recycled’.)

  Here’s the head-gear: first reduction from the motor-shaft to the layshaft, then (duplicated) reductions to the head ...

  And tail...

  The chunky wooden blocks are bearings.

  The next thing to say is that there has to be some way of controlling the motor from both ends (unless your arms are six feet long).  Arachne has two switches, the little toggle one at the left to start, and the white plastic one at the left to stop (both recycled).  Control by voice or willpower would be nice, but that’s for future updates. 

  Now let’s make a string:  Set the head switch to ‘off’ and the tail switch to ‘on'.  The core has an eye put on in the usual way, and is fixed to the head-drive with a screw through the U-shaped coupling:

  The tail of the string is long enough to go through the hollow tail-drive, into which it is clamped with a screw.  Pull it nice and tight.

  Now the clever bit (acknowledgement to Lucy Coad).  Bash a gentle ‘flat’ on the string, where you want the winding to stop.  Allow about three turns round the wrestpin. i.e. pin-to-pin length plus about 2”.  This is called ‘swaging’, and helps to stop the core coming unwoggled.  Remember where this flat is (at about 61½” on this example).

  Now loop the cover-wire round the bolt holding the eye, and make a few starting turns by hand.

  Now concentrate.  NO interruptions or distractions.  Hold the coil of covering wire with your right hand, so that your hand acts as a brake.  Switch on.  Support the core firmly against your left thumb, and pull quite a strong tension on the coil.  Do not allow the string to wander towards you, or to bend.  Use the stripes on the bed as a guide to keep the pitch correct and constant (you can make striped guides at diferent angles).  Walk along towards the right as the winding proceeds, and take care not to tread on the cat.

  When you get to the place where the flat is, close up the coils and switch off.  Three hands are best for this, but the left hand can be spared for a quick dash to the switch.  Under no circumstances let the cover wire go loose on its reel.  (This will put the next string at risk, as the coils will get under each other, and not feed properly).  Now hang on to the cover wire on the reel, support the swaged bit with your thumb, and pull hard to break the cover.  It will break at the string, and this is the best way of getting it tight. 

...And there’s our string!

  Wearing a white cotton glove is not essential, but it looks cool, and keeps sweat off the string.  It also makes your thumb last a bit longer.

  Finally, set the head switch to ‘off’ and the tail switch to ‘on’ ready for the next string.

  As with many of  life’s endeavours, a bit of practice leads to improvement.

  You will have noticed that Arachne makes strings with a right-hand thread, which seems logical to me.  Some original strings are left-handed, though.  If you are left handed, it might be easier to make the whole thing the other way round.

  I’m not claiming that these strings are perfect, but they work for me, and it’s a lot of fun!  Also quite a bit cheaper than buying them...

  Good luck!

  David Hackett

  October 2009

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A short addendum to the story of Arachne by David Hackett.

I had been content to order the over spun strings from a supplier here in America as I always imagined the set up to make such a string was too capital intensive. But hearing that David made his own led me to ask how he managed it, and his story of the development of Arachne was extremely useful. Being an engineer myself, I could imagine making such a device for a very economical price, compared to the $10/string charge that I was paying. On a Broadwood square of 1793, this amounts to 26 strings and so $260 for the set.

Following all of David’s lessons learned, I went a few steps further just to see if I could describe a winder that could be built without relying on specific scrounged parts. Power is obtained from a hand drill motor, mounted on a 2” X 8” X 8’ pine timber as found in any building supply house for under $10.00. A cheap hand drill motor is sufficient as a power source, making sure to get one with a relatively low maximum speed, such as 600-900 RPM. A variable speed is handy for final adjustment.

Just as with Arachne, wood blocks make excellent support and bearing members. Since I was using ¼” drive components, I drilled the blocks out to one size under ¼ inch then finished the hole with a ¼ inch coarse bar stock to heat harden the wood, though you can skip the step in my opinion. A 3/8” relief counter sunk on each side is made, leaving about ¼ inch of the wood to make the bearing, and relieves the bearing surface so that exact placement of the wood block is less important. You only want to support the drive shaft or wire tension shafts with as little binding as possible. A good moly grease used liberally results in very smooth operation. The drive rod was a 6 foot long piece of ¼ “A2 polished steel shaft. It costs only a few dollars more and makes a great drive shaft.

I also stepped down the RPM by choosing the drive pulley sets to give about a 2 to 1 RPM reduction, which allows the drill motor to be used at closer to full output, and results in higher possible torque. The drill can be held at a fixed trigger depth with a tie wrap, or you could provide a cam to hold it at various speeds depending on personal comfort. In general, it seems to work best to wind at the highest speed you can keep up with. There is less time to lose concentration and vary the angle or string position.

Rather than bother to remember to reset switches, I used three way switches from the building supply store such that the machine can be turned on and off from either end independently.

I also provided a good hand rest bar along the winding path that allows close control of the winding.

For making the flat at the tuning pin end, I mounted some scrap A2 steel plate on a wood block that is just the height of the string, and can be slid under and tapped firmly with a ball peen hammer.

Running at about 400 RPM, a string takes around 3 minutes to wind. That seems to be a comfortable speed for me. The pitch of the over spun is controlled by the angle that the string is held and the position of the core string towards or away from you. If the pitch is uniform, your finger will remain in the same position relative to the over spun string paying off the whole way. If it gets ahead or retards, you are varying the pitch of the over spun. The overspun on a 1793 Broadwood varied between 1.3 mm for the lowest FF, to 1.8mm for F.

I did try making a guide that would keep the pitch constant as it ran along the hand rest, but really, it seemed better to just concentrate on keeping the angle constant by eye. There is considerable variation in original strings that I suspect was common, as this was a job often given to wives and children of builders to do!

The materials for this project are captured below. Not included was a piece of scrap oak I used to make the bearing blocks. I happened to have a cordless drill that was unusable because the batteries are obsolete, and a good DC power supply, so I substituted these for the new drill motor. If you buy the new drill motor, count on picking up an outlet with a third electrical box, a power cord, and cover plate so you can just plug your string winding lath into that.

Thanks to Tom for this.  It's the usual story: we British invent something, then leave it to the Americans to make it properly!
 

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