At Fareham & Disctrict MRS we have been refurbishing and extending Fairhaven Town, a layout bequeathed to the club a number of years ago and which uses DIngham couplings. The upgrade is almost complete and attention turned to the legacy stock and members vehicles and their couplings. Dinghams were new to me and I travelled up a steep learning curve as I fitted them to some of my own stock. I also developed, built and tested the replacements for the original current-heavy electromagnet uncoupling units.

The new units use a servo to rotate a neodymium magnet to the underside of the baseboard. I made some gauges to check the coupling heights based on the Dingham instructions and these were used to check the couplings on stock.

The club held a small community show. It was Fairhaven’s first trip out which, unsurprisingly, revealed a long snag list, including issues to correct with our Dingham couplings. It also highlighted that I was not as far along the learning curve as I thought!

I went away and after a combination of thinking, talking to Dingham users at exhibitions and experimentation I reviewed my knowledge of Dinghams and the essential factors to achieve a high level of reliability.

The coupling heights on vehicles must be consistent within a small margin. The allowable margin is difficult to determine precisely but I would guess that a margin of 1.5mm (which potentially represents two adjacent couplings being 3mm out of kilter) is probably pushing it a bit. The standard DIngham height as per the instructions is 24.5mm above rail top to the centreline of the coupling stem; this would be consistent with the standard buffer/coupling centreline. Actually, if you do not need your stock to operate on anyone else's layout you could choose a level a millimetre or two higher or lower but you must be consistent.

If a wagon loop coupling is much lower than 24.5mm, the loop may not rise over the adjacent wagon's hook end and therefore not couple. The wagon is likely to stop with a jolt. If it is too high the loop may not drop adequately into the hook. Equally, a low hook end may be too low for the adjacent wagon's loop to drop into the hook and therefore will not couple. Over-high couplings cause the same problems only the other way round.

The height of the loop end coupling is generally a bit less critical as the loop can be bent a little above or below the hook centreline to the 24.5 mm or desired level because the hook on the loop coupling does not really play much of a role.

If you have wagons where the buffer level varies a bit (most of us do) you could either extend the coupling slot or cut and adjust couplings with a bit of soldering and reinforcement to move the hook higher or lower. Smallish variations can be dealt with by angling the coupling a little through the coupling slot.

Do not forget also that the horizontal position of the tip of the hook is also important. The instructions say it should be in line with the buffer faces but I have found that having the loop end hook 0.5 to 1mm behind the face helps reliable operation. If either hook is too far out, when the wagons are propelled, then the end of the loop can get caught under the flap hinge and cannot lift up; too far behind and the loop can catch on the small return on the top front of the hook and will not lift.

Sprung buffers can compress and affect the spacings mentioned above, especially with heavier stock/trains. This allows the gap to close too much, leading to the issue described above. Lightly sprung buffers, especially with light wagons, can cause bounce, which can result in unwanted recoupling. Many users fix their sprung buffers with a small blob of Evo-stick or similar, which can be easily removed later if necessary.

And, finally, it is vital that the flaps fall back as near 100% reliably as possible. A coupling whose flap does not fall will never uncouple automatically and will not stay uncoupled.

Originally, my testing unit focused on coupling hook and loop height but once the importance of the horizontal position was realised it was improved. A picture of the unit is shown at the top of the page. I used materials I had to hand but similar alternatives can be used, provided the critical Dingham dimensions are adhered to.

A base was made 400 x 100mm from 6mm ply with 10 x 32mm softwood sides. The 6mm thickness was chosen to replicate our baseboard thickness and a length of (PECO) track was laid centrally along it. Later a lid was made from 4mm ply, for protection during transit.

Two coupling carriers are made as follows. Use 50mm pieces of 30 x 20mm aluminium angles and cut a slot 14mm wide by 10mm deep in the middle top of the longer side. Drill and tap two holes 4BA, and tapped 4BA positioned 24.5 mm above rail top and 40 mm apart (corresponding to the standard buffer position). Drill and tap two more holes 8BA, approximately 12mm above rail top and 14mm apart. Finally, drill two holes about 23mm in the ‘short’ leg, to take woodscrews to secure the carriers in place. Loosely thread two 8BA bolts and washers into their holes. Screw two 4BA bolts carrying lock nuts into the buffer holes, adjusted to be 12.5mm out from the angle and locknutted in position. Insulate the underside of the coupling carrier with a strip of insulation tape.

Two coupling strips are made by cutting 20 x 10mm nickel silver or brass strips, 0.020in, I think. They should slide closely between the two 8BA bolts on the coupling carriers. Carefully cut a vertical slot in the centre of each carrier and solder a loop and a flap Dingham coupler square in both directions, with the pips on the coupling shaft against the strip

Slide the two strips, each with a different coupler, under the washers on the carriers and secure loosely in position. Screw one carrier square across the track at each end of the test unit so the coupling is central.

Now, the important bit! It is important this is done well, as it will determine the correctness of all couplings. Set the centreline of the coupling shank 24.5 mm above the rail top. I did this by measuring the thickness of the aluminium angle with my vernier, subtracting this from 24.5 and adjusting the coupling centre height above the angle to this value. I checked the coupling was level by measuring at two points close to the inner and outer ends of the coupling stem. The holes in the shank can be used to judge the centreline, otherwise you could measure the width of the shank and add half to the value, then measure to the top of the shank. Once happy, tighten the 8BA bolts making sure the coupling does not move.

Also, check the horizontal position of the tip of the hook which should be in line with the ‘buffer’ faces; adjust as needed. It is usually easier to adjust the buffer position but make sure both sides are the same. Check that the loop is level and 24.5mm above the rail.

I made a dropper checker from 1mm thick material with a spacer to fit between the rails. The dropper should extend to 1mm above the railhead. At some time I will probably install a permanent gauge between the rails.

I also made a loop height checker which is 24 mm high above rail, also with a between rail spacer. Strictly this should be 24.5mm but there is a bit of flexibility especially with the short upturn at the front of the loop.

The final improvement I made was to make a sliding tray to fit under the flap end, which carries one of the magnets we have standardised on, a 25 x 10 x 3mm N52 neodymium. I used some spare Correx corrugated plastic for this.

So, how do we use this tool? All vehicles go through the following check.

1. The vehicle is placed on the track and the dropper height verified.
2. The loop height is tested.
3. The vehicle is now run to the loop end of the tool and satisfactory coupling confirmed.
4. Again, holding the vehicle lightly in contact with the buffers, flip the loop on the fixed station coupling upwards with a piece of wire or small screwdriver, confirm it is not restricted and that the flap on vehicle falls reliably to prevent the loop recoupling and
5. the vehicle can be moved away, uncoupled.

During the check look out for components on the vehicles which might interfere and compromise coupling operation, vac pipes etc With very little practice this process becomes quite quick. I think we will be introducing a rule that vehicles which have not been checked will not be allowed on the layout, with one or two exceptions for DMUs, fixed trains/sets etc and this will improve our operations enormously. The addition of the Dingham Check Tool has standardised and simplified the whole process.