Design of the Alex Jackson coupling



This coupling was invented and developed by Alex Jackson, a member of Manchester Model Railway Society, in the 1940s. It has become widely known and used in most scales. This article gives an outline of its main features and details of its manufacture for 7mm scale.

Figure 1 gives a coupling hook dimensions and angles. The hook-bending jig, Figure 2, is an aid to correctly bending the hook. The sequence of bending is given in Figure 3. 24 SWG (0.022in., 0.55mm) spring steel wire was originally recommended, which needs a length of coupling of about 100-110mm for adequate flexibility. Some modellers are now using 0.018in. (0.45mm) diameter plain steel guitar strings, for which the cantilever spring length reduces to 85-90mm.

Figure 1. The hook.



Figure 2. Hook bending jig.



Figure 3. Bending the hook.

Coupling is achieved merely by pushing vehicles together until the adjacent hooks meet and interlock. Uncoupling is by drawing down one hook of a coupled pair while the vehicles are being pushed, i.e. with the coupling slack, using an electromagnet below the track. Once uncoupled, the vehicles can continue to be pushed, then separated further along the track. Figures 4 and 5 show the coupling and uncoupling action. One electromagnet will serve a fan of sidings, see Figure 6.

Figure 4. Coupling.



Figure 5. Uncoupling.



Figure 6. Position of uncoupler.

An armature or dropper is made from 2mm diameter soft iron and soldered to the shank of the coupling. This is shown on the left hand wagon in Figure 7. An alternative form of dropper shown on the right hand wagon and in Figure 8. This is U-shaped and hung loosely from the coupling wire and is located by the axle. It can be made from soft iron wire as sold by florists of roughly 0.9mm diameter. When the electromagnet shown in Figure 7 is energised, the dropper is pulled downwards and this disconnects the coupling. The electromagnet (Figure 9) is wound on a soft iron core (perhaps a cut-down large nail), with about 5000 turns of 32 or 34 SWG (0.010in., 0.25mm) enamelled wire, giving about 100 ohms resistance, energised at 12 volts. The SEEP electromagnet Type EM/1 can be used successfully, either on the standard 12v DC or on 24v DC. The higher voltage makes the distance to the dropper less critical but may limit the life of the electromagnet.

Figure 7. Uncoupling with electromagnet.



Figure 8. The alternative dropper.



Figure 9. Electromagnet.

The coupling should be set at a shank height of 17.5mm above rail level. It is important to set all hooks against a master gauge. Adjusting one hook against another is not wise. Couplings on locomotives may be non-operational hooks if space is limited, uncoupling then being achieved from the adjacent vehicle. However, as this gives rise to problems of uncoupling double headed locomotives, operating couplings are always to be preferred where space permits.

Curves of very sharp radius can inhibit successful operation by preventing the hooks interlocking when coupling, by creating a turning moment about the vertical axis of the vehicle on four-wheel vehicles because of the offset of the couplings. Curves of four foot radius or more are unlikely to be troublesome in this respect.

The principal advantages of this coupling are:

Acknowledgments

Redrafted from Manchester Model Railway Society sources, whose permission to do this is gratefully acknowledged.