This month's Short Talk was by Jim, who had whetted our interest in how he makes Alec Jackson couplings in 2mm scale by showing us some of his tools for the purpose at a meeting he hosted a few months back.
AJs in 2mm scale were first written about, as far as I know, by Bert Groves in the May 1965 2mm SA magazine. Jim also used AJs since way back when, and first wrote up his techniques in the magazine in August and December 1994, with an important update in February 2007; and in MRJ (No 79, 1995, p153). However, he referred us to the standard work, the Scalefour Society's "Alex Jackson: the Man and the Coupling" (£6 to non-members), which explains their evolution and dimensions for different gauges, as well as their use in 2mm and Jim's development of the coil version.
We were shown the principle of the AJ with a large-scale model:
To couple, the two couplings slide over each other sideways; to uncouple, over a magnet beneath the track, the two couplings slide downwards and are forced sideways by the angled tail, until they pass beyond the opposing tail, before springing back on its other side when the train passes beyond the magnet.
Steel wire, however, does not work in 2mm scale: the magnetic field passes through both couplings and draws both down, so that they stay in the same relationship to each other and do not uncouple. Jim therefore started making his couplings - pre-coil - from 0.006" (0.152mm, 38swg) hard-grade phosphor bronze wire, softened slightly by quickly flicking it through a match flame - not enough to heat it to red heat, which makes it completely soft, in which state it is useless. Without this slight annealing, there is a tendency for the wire to fracture when it is doubled back to form the hook.
An early "conventional" AJ'd wagon using 6 thou PB wire was produced for inspection. In general, Jim works to half the 4mm dimensions, rounded up to the nearest quarter-millimetre.
Coming back to the coil version of the coupling: the idea was to produce a highly flexible coupling in minimal space, by coiling up the 60mm length of spring wire which had proved insufficiently springy in the conventional version - there was a tendency not to couple up due to lack of sideways movement. Several experiments were tried to overcome this, including use of thinner wire and hinged couplings, but eventually the coil turned out best: so well, in fact, that the wire thickness could be increased to 0.008" (near enough 36 SWG, 0.193mm) which, handily, is available from Eileen's Emporium. This also had the major benefit of making the hook more robust. Making the coil is quite fiddly however, as Jim's demo showed.
First a 60mm length of wire is cut off, and any burrs stoned off the end until it feels completely smooth. The wire is cut is straightened by placing the ball of a finger into the curve of the wire, then drawing the full length of the wire through finger and thumb applying gentle pressure from the thumbnail. After a few passes the wire is straight.
The first job is to form the hook at the end of the coupling. This is simplified using a tool made from brass rod, with a 2.7mm-deep hole, able to take a single thickness of wire, drilled at one end to help form the first bend in the hook, and a 1.5mm hole, able to take a doubled thickness of wire, to help form the second.
The doubled-back part of the tail is strengthened by dipping it in solder paint and touching with a soldering iron. This avoids any roughness which might hinder the sliding action in coupling and uncoupling.
A 1mm-deep step is then added at the correct distance. The first 90° bend is made with pliers, ensuring correct orientation with the hook; then a small steel rule which happens to be 1mm thick is used to help form the step.
Next, the coil is wound around a length of 1.4mm steel drill rod. The rod has a handle of brass angle attached, with an adjustable clamp and small slots in whcih the hook of the coupling engages to produce a variety of coil-to-hook lengths.
The rod is then held loosely in a pin chuck, so it can rotate; the chuck is clamped in a vice.
The coupling can then be wound using the brass handle to rotate the drill rod, keeping tension on the wire:
Since the wire is a standard 60mm length, a shorter coupling will have a larger coil. The finished coil can now be gently eased off the rod.
Now, with the coupling held horizontally, all the angles are checked and corrected if necessary.
Next, the coupling is mounted on the vehicle using superglue. (Jim uses cheap superglue tubes from pound stores, pricking the tube top then squeezing a little onto a metal plate. the excess is wiped off the tube and Vaseline applied to tube and top; the tubes are then stored upright and are cheap enough to throw away without regret when they harden).
To glue the coupling in place, the wagon is strapped into a little jig, the coupling held in place, and a drop of glue flooded onto the wagon floor, without gluing up the coil.
A drop of superglue is placed in the U, then the nail is placed on the coupling as close to the wheel axle as possible, set not quite vertical so a little sideways motion is imparted when a magnet attracts the dropper, to aid the uncoupling action. The nail is positioned with tweezers then held in place until the glue goes off.
One advantage of the coil design is that it makes the coupling very flexible in storage, with less change of damage or distortion which later causes problems in operation. This was demonstrated using a clear plastic box, so we could see how the coupling was simply pushed sideways without damage when pressed against the box wall, but returned to the normal position afterwards.
Jim has completed more than 300 of these couplings. Practice makes perfect!
To bring the story up to date, Jim gave a brief glimpse of the coupling R&D department - however, cameras had to be left at the lab door, so no pictures.
That brought a fascinating demonstration to a close, and allowed a little more work to take place on Sauchenford's fiddle yard.
Alisdair has also been working on scratchbuilt bogie (or pony truck?) wheels for his latest Highland loco. I can't remember if this was to be a 2-4-0 or a 4-4-0, but the wheels are made in his Unimat, with brass centres and steel tyres. The prototype diameter here was 2'6" I think.
Jim showed us his 2mm scale signal wire posts - etched posts with pulley wheels from slices of copper wire - which he has written up recently on RMWeb.
And so we came to the end of the meeting. Thanks very much Stephen for hosting and for the refreshments. Next month, we plan to meet in Edinburgh.
