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The 7mm Dingham Autocoupler
Assembly and Fitting Instructions

The instructions for the 7mm Dingham Autocoupler are included here to give prospective purchasers the best possible idea of the coupler, its mechanism and exactly what is involved in assembling and fitting it.

The instructions below are not an exact replication of the printed instructions. In particular, the quality of the illustrations is inferior to the printed version. However,by clicking on this link, you can open a pdf version of the instructions and print it out for yourself. You will need a pdf reader installed on your computer. If you do not already have a pdf reader you can download and install Adobe® Reader by going to www.get.adobe.com/reader/

The coupler is intended for single-ended use. This means vehicles must always face the same way on the layout. Each vehicle has a hook with loop at one end and a hook with latch at the other. Coupling takes place automatically as vehicles are pushed together. The loop slides up the hook on the next vehicle, passes under the tip of the latch and drops into the slot in the hook. Uncoupling can take place when vehicles are buffered-up by means of magnetic action on a dropper suspended from the tail of the loop under the buffer beam. The magnet pulls the dropper down and the loop is lifted, flipping the latch upwards, then dropping back on top of the latch and preventing re-coupling. Properly adjusted couplers on 4-wheel wagons will couple and uncouple readily on curves of 4ft 6in radius or less.

Two types of latch are provided on the fret. Try both and see which you prefer. Type 1 is less obtrusive and its operation is slightly more reliable, but type 2 is probably easier to assemble and fit.

IMPORTANT:  For dependable working, the coupler relies on properly adjusted buffers on vehicles. If buffers are too long, it may be difficult to couple vehicles on curves. If buffers are too short, the coupler loop will be pushed against the back of the slot in the opposing hook when propelling, and the friction between loop and hook will prevent the loop lifting and uncoupling. For the same reason, uncoupling may be unreliable if buffer springs are soft enough to compress during normal shunting. The short hooks and loops, intended for some industrial locos (8.5mm buffer length), are a compromise, because 8.5mm is insufficient space to accommodate the Dingham geometry. The short loop will couple and uncouple with standard hooks, but the short hook will suffer loop-hook contact. This problem will be lessened if the type 1 latch is used with the short hooks.

NOTE: THE COUPLERS SHOULD BE CHEMICALLY BLACKENED ON COMPLETION. THEY WILL NOT WORK IF PAINTED. Carr’s metal black for nickel silver is suggested. Clean and degrease the couplers before blackening.

Hook with Loop (diagram below)   

(a)     Prepare the hook. Solder a short piece of 0.8mm brass wire into the pivot hole in the hook. (Make a simple jig by drilling a 0.8mm hole about 2mm deep in a piece of wood).  Trim so that about 1.5mm of wire protrudes each side of the hook and remove burrs. (A jig made by drilling a 0.8mm hole through a piece of 1/16in brass strip is useful here). Remove the upper half-etched latch stop. If fitting to a vehicle with 10.5mm buffer projection, remove the lugs on the shank. Retain the lugs for 12.5mm buffers.

(b)    Prepare the loop. Bend the pivot lugs upwards through 90deg (half-etched lines inside). Bend the front of the loop upwards at about 45deg. Bend the tail of the loop downwards through 90deg making the bend as close to the body of the loop as possible. Bend the last 5mm of the tail back to the horizontal and (optionally) put a 90deg twist in it to bring the eye at the end vertical. With a cutting broach or 0.9mm drill, open up the holes in the pivot lugs to give a sloppy fit on the 0.8mm wire.

(c)    Fit loop to hook. Holding the loop vertical in relation to the hook, place one pivot hole then the other over the pivot wire. If necessary, part the pivot lugs slightly to do this and squeeze them gently back into position after fitting. Swing the loop into its normal position as shown in the diagram and bend the half-etched stop sideways towards the tail of the loop.

(d)    Fit a magnetic dropper. Make a magnetic dropper from the 0.7mm soft iron wire supplied. Trim its total length to 17mm. It should clear the railhead by 1mm.

Hook with Type 1 Latch (diagram right)

(a)    Prepare the hook. Remove the lower half-etched loop/latch stop. Depending on buffer length, remove or retain the lugs on the shank (see above).

(b)    Prepare the latch. Fold the latch around the edge of a piece of fret material (half-etched lines inside) to ensure the correct distance between the legs. Pass a length of 0.8mm wire through the two holes in the latch. If the wire and latch are not at 90deg, push the latch gently sideways until they are. Take a 3mm length of the 0.8mm-wide strip, insert into the latch as shown and solder. Alternatively, fill the end of the latch with solder. Remove any projections carefully. They may impair the working of the coupler. With a cutting broach or 0.9mm drill, open up the pivot holes to give a sloppy fit on the 0.8mm wire.

(c)    Fit latch to hook. Flatten about 0.5mm of one end of a piece of 0.8mm brass wire by squeezing in pliers. Position the latch over the hook and pass the wire through the pivot holes in latch and hook. Cut off the wire 0.5 – 1mm from the opposite side of the hook and flatten this end also in the pliers. Fold the upper latch stop sideways.  

Hook with Type 2 Latch (diagram right)

(a)    Prepare the hook. Prepare the hook by soldering in a pivot wire in exactly the same way as for the hook with loop.

(b)  Prepare the latch. Bend the pivot lugs upwards through 90deg (half-etched lines inside). Bend the tail of the loop downwards through approx 45deg. Open up the holes in the pivot lugs with a broach or 0.9mm drill to give a sloppy fit on the 0.8mm wire.

(c)  Fit latch to hook. Use the same method as described for fitting the loop. Bend the half-etched stop sideways, towards the latch tail then adjust the angle of the tail until the latch is almost vertical when the tail meets the stop.

Fitting Couplers to Vehicle  

IMPORTANT: check the lengths of the buffers on your stock – sprung buffers should be adjusted to either 10.5 or 12.5mm projection. For all buffer lengths, the couplers must be fitted so that the hook projects the same distance from the beam as the buffers, or up to 0.5mm less (see diagram below). THE CENTRE HEIGHT OF THE COUPLER POCKET SHOULD BE 24.5MM ABOVE THE RAILHEAD. If it  differs much (more than about 1mm) from this height, remove the existing pocket, drill a 2.5mm hole at the correct height, and use one of the etched pockets provided.

The couplers are fitted in the same way as the usual 3-link or screw couplings – through the coupler pockets in the buffer beam. They should be secured by soldering or by adhesive (cyanoacrylate or epoxy). Holes are provided in the shank for fixing by spring and split-pin or by the spring-wire method used in Peco kits. However, rigid fixing is much to be preferred, because it gives positive positioning and more reliable operation.

If no coupler slot or pocket is provided, or if it will not fit the shank on the hook, drill a 2.5mm hole through the beam centred at 24.5mm above rail height. Cover it with one of the pockets provided on the etch, and fit the coupler through the slot in the etched pocket.

Double-Ended Operation

On many layouts, rolling stock is never turned, so single-ended couplers are no problem. However, to allow locos to be turned, it may be possible to fit double-ended couplers. A loop and a type 1 latch (but not a type 2 latch) can be fitted at both ends of the loco as shown in the diagram left. In assembling double-ended couplers, first solder the pivot wire into the hook. Then bend the type 1 latch until the eyes on the ends are about 3mm apart and place over the pivot wire. Squeeze the latch together over a 3mm length of 0.8mm-wide strip and solder in place. Finally add the loop in the usual way. It is emphasised that the couplers will almost certainly not work as well in this set-up as in single-ended mode.  

Operating with Dingham Autocouplers

Electromagnets are recommended for actuating Dingham Autocouplers. Suitable magnets are available from several suppliers, or may be home-made. Permanent magnets, with a lifting and lowering mechanism (lift the magnet to actuate the couplers), may also be used. If using permanent magnets, make sure that a pole of the magnet is facing upwards. (The magnetic field is strongest near the poles).

Examples of operation are given below.

Example 1: A passenger train enters a station where the service terminates and the loco runs round. The train is stopped with the coupling between loco and train over a suitably placed magnet. The loco now eases back on the train (a movement of about 3 – 4mm and quite prototypical, because the buffers have to be compressed to allow the screw coupling to be unhooked). If the magnet is now briefly energised, latched uncoupling will take place, and the loco can move away from the train at any time.

Example 2: For shunting a yard, magnets can be placed at the entrance to a fan of sidings. Only one electromagnet may be required, though it is often advantageous if several are provided. As a train is propelled into the yard, any coupler may be uncoupled by energising the magnet as that coupler passes over it. The vehicles will remain uncoupled so long as they are propelled steadily.

Example 3: The diagram below shows the arrangement of magnets on the layout for which the Dingham Autocoupler was developed.


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Last modified: 16 October 2013