Alex Jackson Coupling - page 4

Back to page 3

Modern developments
As originally conceived by Alex Jackson each coupling was fastened at the centre of the wagon or bogie and uncoupling was by mechanically pushing one coupling upwards. The change to pulling down rather than lifting up to uncouple was made in order to overcome problems of lifting the vehicle as well as the coupling. The change to fasten at the far end of the wagon was made in order to gain greater flexibility of the wire for magnetic uncoupling, without decreasing the wire diameter.

Such development, if slow, has been continuous since the coupling's inception and since the information in the first article was last published, other developments have taken place. While the magnetic version of the coupling as described works with complete satisfaction and has done so for many years on a number of notable layouts, it is also true to say that a number of features are capable of improvement.

The coupling wire with an unsupported length of some 65mm (2.5 inches) is vulnerable when stock is continually having to be packed and unpacked for exhibition work; also, the fact that four wheel vehicles are pulled from the opposite end to the coupling hook has caused some difficulties, particularly on sharp curves and with heavy trains. The adjustment of the shank to achieve 10mm above rail (without a height bar) requires a fair amount of skill and practice, which not all modellers seem able to develop. The design of the coupling means that it must be purpose built for each vehicle and fitting is not easily adjustable to meet all the critical dimensions.

Methods of overcoming these difficulties have been sought over the years and what follows is a description of a later design which has been extensively tested and which we feel can be recommended. The earlier methods need not be discarded as the two methods are quite compatible - it is open to the modeller to follow whichever method he prefers, or finds suitable; indeed both may be used in combination .

Radical re-thinking
A method of anchoring the coupling on the transverse and longitudinal centre lines of the vehicle,or as near as possible, was achieved by hinging the wire at that point. Early attempts to improve wire flexibility had the wire hinged at the centre and then extended to the end remote from the hook, such that this end flexed upwards when the hook was pulled down. This was not totally successful but led to the idea of using gravity as a constant force by fitting a counterweight to this remote end, so that the weight was raised as the hook was drawn down. This worked satisfactorily and led to the further refinement of mounting the hinge on an adjustable plate, making it easy to locate the hook tail relative to the buffer faces.

The height bar described earlier is an integral part of this design as the counterweight holds the shank of the coupling against the height bar and adjustment for coupling height is always by adjustment of the height bar rather than of the wire. The shorter free length of wire makes the coupling more robust without losing the delicacy of action. An early error in these experiments was the attempt to try to achieve a point of balance between the armature and the counterweight in the belief that this was required for correct action. In fact the counterweight has two purposes; to hold the couplings shank against the height bar and to supply a source of inertia to the coupling when in the act of coupling or uncoupling. Without sufficient inertia both couplings tend to dip when coming into contact at coupling; similarly, when a coupling is drawn down by the magnet for uncoupling, its fellow coupling must have sufficient inertia to remain in the normal position. The counterweight must therefore be relatively heavy compared to the armature at the other side of the hinge.

Detailed design
Having established the method as a sound working proposition, it was thought necessary to devise a fairly standard type of fitting for vehicles, with the intention that, where possible, parts could be produced in bulk from standard materials. That said, there is nothing final about these designed parts and they may be freely adapted as long as there is no departure from the principles. As an example, the base plate described later for use with four- wheel wagons will not fit wagons with fully modelled underframes but it should be possible to mount a hinge plate directly on the underframing

The hinge
Two types of hinge have been used, one utilising a short length of 23 gauge hypodermic needle as a tube through which the coupling wire is threaded so as to provide a pivot point, the second using two holes of 0.3mm (0.012inch) diameter in a small bracket bent in such a way as to provide a similar pivot point to the hypodermic needle. The following photographs show the two types.

Hinge plate

Photo C The needle or bracket is soldered to a small brass plate which has a 12BA slot and one edge turned at right angles away from the pivot.

Mounting
The hinge plate is mounted on a base plate made from standard section aluminium 1/2 inch by 1/8 inch. A length of 3/4 inch will fix nicely to the bottom of a typical four-wheel wagon and with two 12BA tapped holes will accept the hinge plates of both couplings, one 12BA screw per coupling being quite adequate to secure the hinge plate with the folded lip maintaining alignment against the base plate edge. The longitudinal slot in the hinge plate allows adjustment of the tail to buffer face dimension (0.25mm or 0.01 inch). Photograph G shows an adjustment being made.

For bogie vehicles, 6 wheel vehicles and other less than standard vehicles, then single coupling base plates can be made to suit the mounting conditions or, in some rare cases, it may be necessary to produce a non-standard hinge plate or even to make the hinge a fixed part of the vehicle. Such an arrangement causes loss of the ready adjustment of tail-to-buffer face dimension referred to earlier but the hinged version of the coupling is more readily adapted to unusual vehicles than is the 'flexy' version.

Photograph H shows how the hinged version has been adapted to fit a coach bogie.

The armature (or dropper)
The armature length is fairly critical. If too long, it will lock on to the magnet face and cause derailment; worse, it may also cause distortion of the wire and lead to the need to reset the coupling; even longer and it will possibly catch on rails at turn outs etc. with similar quite drastic results. If too short it, may fall outside the influence of the magnetic field when uncoupling is attempted.

The length is dependent on rail height and wheel diameter and can be calculated from:

(rail height+y+10mm) - (x+0.5mm)

where 'x' is down movement of wire before touching axle and where 'y' is the depth of slot sawn in the armature to aid its fitting (see next paragraph). So, for example, for 12mm diameter wheel on 2mm diameter axle to run on track made from code 75 rail which has a height of 1.9mm, - i.e. 3mm movement - armature slot depth 0.6mm:

armature length=(1.9+0.6+10) - (3+0.5) = 9.00mm

A 1 inch (nominal 25mm) wire nail, about 0.072 inch diameter offers suitable material to make one armature and one counterweight. If the nail is a large headed type then the head is removed or reduced, an accurate length is cut from the nail and a small slot sawn in one end across a diameter this to receive the wire (Photograph I). This is the armature or dropper, and is soldered to the coupling wire at a point which will allow the armature to lie inboard of the axle by 1 or 2mm as shown in Photograph J.

Counterweight
The remainder of the nail, with the point removed, will provide a piece about 12mm long and is soldered at the far end of the coupling wire at a point which will allow it to lie inboard of a wheel and above the axle, see the photograph. For normal four wheel wagons, the mass of this portion of nail, fitted as described, is usually sufficient to balance the dropper and to provide sufficient inertia to overcome the friction force of the coupling tails when coupling or uncoupling.

It is possible for the counterweight to be too light, or to be fitted too close to the hinge, but still to overcome the weight of the armature and maintain the hook at the correct height, though not providing sufficient inertia to overcome the friction forces of the coupling tails. This will cause problems when coupling or uncoupling. However, it is also possible for the counterweight to be too heavy or fitted too far away from the hinge, causing upward forces at the armature which are too large to be overcome by the downward forces set up by the uncoupling magnet. Experience achieved by a little trial and error will soon find the correct weight/position!

Etched components
Norman Whitnall and Dave Booth fully described the coupling in the Model Railway Journals Nos.55 & 56. Since then Branchlines have produced an etch which has 10 hinge units which fold up to give two tabs with 0.4mm diameter holes to provide the fulcrum point. In retrospect, 0.3mm holes would have been a better choice but a good few modellers have found these etchings to be a useful addition from our trade. At the time of writing these etches are still being sold by Branchlines.

Another very useful etching, to a design by Graham Turner, helps to make a jig which holds the hook in correct location with the buffer faces and vehicle centre line leaving both hands free to be used in soldering the wire to the vehicle. Mr Turner has developed two further intriguing little aids to assist with the production and fitting of the coupling. The first approaches the forming of the coupling in a slightly different manner but ensures that greater consistency of production is achieved. The second holds the armature (dropper) against the coupling's shank in a truly vertical position, again leaving hands free for soldering the two together. Both jigs and the forming tool in particular appears to overcome most of the problems encountered by some modellers when using the earlier designs of form tool.

Various jigs are also available from the Palatine Models website.

Epilogue
That, then, is the full story of the Alex Jackson Coupling to date. Its development within the Manchester MRS will continue and when each new idea has been proved it is more than likely that details will be published in the model railway press.

We are aware that others have carried out their own process of development, particularly in other scales, and the authors would be happy to act as a clearing house for all information about the Alex Jackson coupling. Any modellers who have proven details about the coupling which could usefully be used by others are invited to send such details to us via the webmaster. In this way a library of information could be built up and be made available to all who may be interested, with due credit to the originator.