This page was created by Chris Free using text from the now closed Dingham Autocoupler website
(© Copyright DINGHAM 1999. All Rights Reserved).
The line drawings are mostly from Dingham and the photos and video are by the author
To ensure continuing supply the Guild has arranged to take over distribution following the retirement of its innovator, Trevor Shaw.
To order the couplings go to the Guild Home Page, click the “Products” tab and then “Guild Modellers Products” or follow the link below.
The Dingham Autocoupler is probably the least obtrusive commercially available automatic coupler for model railway vehicles in 7mm scale (O gauge) and 4mm scale (00, EM and P4/S4). It also has the advantage of a delayed uncoupling action without the need to move the shunting loco back and forth to operate the delay mechanism.
This photo-sequence shows the Dingham Autocoupler in action.
A. Each vehicle has a hook with a loop at one end and a hook with a latch at the other. Here, the left hand vehicle has the loop and the right hand vehicle the latch.
B. As the vehicles are shunted together, the loop slides up the face of the opposite hook, passes under the latch and drops into the slot in the hook. The two vehicles are now coupled.
C. To uncouple, the vehicles are buffered-up over an electromagnet positioned beneath the baseboards with the top of its pole piece at sleeper height. The magnet pole piece can be seen below the left hand vehicle (marked with red and white tape).
D. The electromagnet is now energised and attracts the iron dropper under the loop, causing the loop to lift. As it lifts, it flips the latch upwards and, once it has passed, the latch drops back to rest on the tip of the hook.
E. The current to the electromagnet can now be switched off, whereupon the loop drops onto the top of the latch and so is prevented from falling into the slot in the hook and recoupling.
F. The uncoupled vehicle can be propelled to any position and left there just by withdrawing the vehicle it was coupled to.
This short video shows the Autocoupler in action
Note that there is no need for the vehicles to be stationary to uncouple. If a string of wagons is propelled over an uncoupling magnet any or all of the wagons can be uncoupled by energising the magnet as the required coupler passes over it. The sequence pictured in photos C, D and E will take place “on the fly”. Despite the couplers being “handed”, uncoupling will take place when the train is propelled in either direction over an energised magnet.
When bringing a passenger train into a terminus station, the locomotive can be released to run round in a most realistic manner. The train is stopped with the rear loco buffers over an appropriately placed uncoupling magnet. The loco is then reversed about 2-3mm, to buffer up to the train – an entirely prototypical movement that is required to allow the screw coupling to be unhooked. If the electromagnet is now briefly energised, latched uncoupling will occur and the loco can be drawn away from the train at any time.
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.
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 left). 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.
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.
The Dingham electromagnets are based on industrial-quality solenoids, which are modified by fitting an extended pole-piece, to reach through the baseboard to the level of the sleeper tops. The maximum thickness of baseboard that can be accommodated without recessing underneath is 12.5mm or 1/2in.
The DC resistance Dingham electromagnets is approximately 8.5 Ohms, which is substantially higher than the 3.7 - 3.8 Ohms of alternative products. This means that Dingham electromagnets take a current of less than 1.5 Amps on 12 Volts DC. They are therefore much less likely to burn out if misused and are also less likely to cause switches to burn out.
Important note The Dingham electromagnets are intended only for operation of automatic couplers in which the moving parts are hinged. These include Dingham, DG, B&B, Sprat & Winkle. They are not powerful enough to operate 7mm Alex Jackson couplings which require them to bend a spring steel wire.
Electrical Supply – The Dingham electromagnets should be operated on a nominal 12V DC supply (usually obtained by rectification of 16V AC).
Switching MUST be via a non-locking push-to-make switch (e.g. All Components Code SPB01, Brimal Components SW561 and SW500 or Railway Scenics 219-200).
Or a non-locking biased-to-off toggle switch (e.g. All Components SPB1 series or Farnel SW06071 ).
The electromagnets will NOT operate on AC.
The magnets are fitted to the layout as shown in diagrams 1 and 2 left.. The pole-piece/bolt may be secured in the baseboard either by drilling a 4.5mm hole and self-tapping the M5 bolt into this or by glueing the bolt into a 5mm hole. If tapping the bolt into the baseboard, use a driver fitted with an 8mm hex socket.
Magnetic force falls off very rapidly with increasing distance from the magnet.
In fitting magnets to the layout, the aims should be to have (a) the coil of the magnet and (b) the pole piece as close to the coupler as possible. ON NO ACCOUNT SHOULD THE TOP OF THE SUPPLIED POLE PIECE EXTENSION BE BELOW THE TOPS OF THE SLEEPERS and if it can be arranged to be a little higher, and disguised, so much the better.
Diagrams 1 and 2 show how the magnets should be fitted to the baseboards. After deciding the set-up, the pole-piece should be shortened to suit before the magnets are fitted to the layout. Do not be tempted to use the full length bolt. It must not project more than 20mm above the two upper washers.
If recesses have to be made in thick baseboards before scenic work has started, they may be made with a chisel or with a spade-type drill (diagram 3). However, after scenic work has been done then great care must be taken and the only type of drill that can be recommended is a type intended for drilling recesses in kitchen cabinet doors to take hinges (see diagram 4). These bits produce a flat-bottomed hole 35mm in diameter and are easily controllable, so may be used with confidence on scenic boards.
The importance of positioning the magnets cannot be over-emphasised. It requires careful thought and experimentation if the most railwaylike (and enjoyable) operation is to be obtained. The positioning of magnets on Lofthouse, the Skipton & District Railway Society’s O Gauge exhibition layout, will be used as an example.
All passenger trains enter Lofthouse from the left in the diagram above and are reversed. Magnet 2 is positioned to release the loco from an incoming train of three 4-wheel coaches, perhaps with a tail load (horsebox, etc). The train is stopped with the coupler over Magnet 2 and the loco is reversed about 3mm, buffering up to the train. Magnet 2 is energised and the loco is released.
Magnet 1 is positioned so that the rear coupler on the rake of three coaches is directly over it when the front coupler is over Magnet 2. Thus, if a tail load is present, the loco can run round, buffer up to the tail load and move it forwards about 3mm to slacken the coupling between the coaches and the tail load. Magnet 1 is then energised to uncouple the trailing load from the coaches and the tail load can be shunted into the yard. The three coaches are not moved during detachment of the loco or the tail load.
Goods trains running left-to-right through Lofthouse use the loop road. They stop at Lofthouse to have the brake van detached and a banker attached to the rear for the steep climb to the right of Lofthouse station. Trains are stopped with the brake van front coupler over Magnet 3. The banking loco, stabled in the short spur next to the home signal (A) then moves forward and pushes the brake van forwards about 3mm to slacken the coupling between the van and the train. Magnet 3 is then energised to uncouple the brake van, which is drawn backwards from the train. The train then moves forwards to clear the turnout leading to the yard and the banker shunts the van into the yard, uncoupling the van as it passes over Magnet 3. The banker is then attached to the rear of the train.
Shunting the yard could be done using Magnet 3 only, but Magnets 5 and 6 are provided to allow more realistic operation (i.e. wagons do not have to be withdrawn as far as Magnet 3 if this would be unnecessary in reality).
Goods trains running right-to-left through Lofthouse use the platform road and are double-headed for braking purposes on the steep bank leading down to Lofthouse. In Lofthouse station, the pilot engine is detached and the train picks up a brake van from the yard before departing leftwards. The incoming train is stopped just short of the starting signal (B) with the coupler between pilot engine and train engine over Magnet 1. A section break coincides with the position of Magnet 1. The power to the train engine is switched off, the pilot engine reverses about 3mm to slacken the coupling. Magnet 1 is energised and the pilot engine is released and parked in the spur. The train then pulls forwards and reverses onto a brake van in the yard, couples up and departs.
Magnet 4, not mentioned so far, is hardly used and is probably unnecessary.
The above illustrates how careful positioning of magnets can play an important role in realistic operation. For example, Magnet 1 must be positioned just over a loco’s length in rear of starter signal B, to allow uncoupling of the pilot engine from right-to-left goods trains. This in turn sets the position of Magnet 2, which must be three 4-wheel coach lengths to the right of Magnet 1 to allow the release of locos from incoming passenger trains and detachment of tail loads without moving the passenger coaches.
Only in certain circumstances, because all vehicles which are propelled over a permanent magnet will be uncoupled and will stay uncoupled. However, if there is a location on the layout where you always want to uncouple (e.g. a loco on a passenger train arriving in a terminal station), then it may be possible to use a permanent magnet. So long as the coupler is under tension as the train comes to a halt over the magnet, it will remain coupled. The loco should then be reversed about 3mm, when uncoupling will occur. This movement is quite prototypical because the loco would be reversed to compress the buffers so as to assist slackening and uncoupling of the screw-link coupler.
There's another way in which you might use permanent magnets. You could install a mechanism to raise and lower the magnet. This will need some experimentation to find the lowered position where the magnetic field is not strong enough to attract the dropper and actuate the couplings. The raised position should be as near the top surface of the sleepers as possible.
When using permanent magnets, be sure to mount them so that a magnetic pole points upwards. Some bar magnets have the poles at the ends and some on the flat sides. Just feel around with a piece of iron or steel to find where the magnetic field is strongest.
This method of attaching the couplers is not recommended because it gives a less positive location than gluing or soldering.
If do you use the spring and split pin method, it is highly recommended that you also use the etched drawgear endplates (coupler pockets) supplied on the Dingham fret. The couplers are a good fit in the etched slots, whereas they are likely to be a sloppy fit in the slots in plastic, white metal or etched kit buffer beams. Before fitting the etched coupler pockets, carefully remove any existing moulded pockets, otherwise the hooks may protrude too far from the headstock.
I use Carrs Metal Black for Nickel Silver, and I normally blacken the coupler components after soldering and folding-up but before assembling the components. Carrs Metal Black for Nickel Silver is available from many model shops and mail order outlets or indeed, directly from its manufacturer C+L Products, who advertise regularly in the model railway press.
Remove any excess solder from the components with files and a glass fibre pencil, then shake the components in washing-up liquid in hot water for a few minutes to degrease. Then, immerse the components a few at a time in the blackening solution. Agitate or brush the components so that bubbles do not cling to either the upper or lower surfaces of the components. If you do not remove the bubbles, you will have unblackened spots on your couplers. Remove the components from the blackening solution when they are dark-brown to black and drop them in clean water to remove excess blackening solution and stop the chemical reaction.
If blackening occurs more quickly than 10 - 20 seconds, the coating will be brittle and will flake off easily. If this happens, dilute the blackening solution, until blackening takes place more slowly and the blackened coating is thinner and stronger.
A method of making couplers with both a loop and a latch is given in the 7mm instructions. Theoretically, fitting such double-ended couplings at both ends of locos which are turned should solve the problem, but it has to be said that the couplers do not work very well if this method is employed. There's simply too much friction between the two loops to allow reliable uncoupling. (It must also be said that this applies to all couplers based on the loop and latch principle).
There are other possible ways around the problem in certain circumstances. For example, there are many end-to-end layouts with a shed and a turntable on which only certain tender passenger engines on certain trains are turned. Passenger tank engines and goods locos are not turned. In such a case, the locos which are turned can be fitted with a hook-with-latch at both ends and the rakes of coaches they work can have hooks with loops at each end. Further development of this idea will allow tail loads to be added to passenger trains, etc.
Short wheelbase vehicles can be coupled and uncoupled on radii of approximately 4ft 6in / 1370mm (7mm scale) or 2ft 6in / 760mm(4mm scale). The Dingham Autocouplers rely on the buffers on vehicles for buffing, just as 3-link and screw couplings do, i.e. the Dingham couplers do nothing to prevent buffer locking. This means that restrictions on propelling and pulling trains through trackwork are the same as for 3-link/screw couplings.
No. The Dingham Autocouplers rely on the buffers on vehicles for buffing, just as 3-link and screw couplings do. This means that restrictions on propelling and pulling trains through trackwork are the same as for 3-link/screw couplings.
The only ways buffer locking can be prevented by an automatic coupler is to build a centre buffer into the design of the coupler or to have an arrangement where a wire is soldered between the buffer heads. I didn't want to take either of these routes when designing the Dingham couplers because, in my view, they are visually obtrusive.
You can fit them to the hook with type 1 latch by drilling a hole through the hook in the right place. I didn't etch a hole because I reasoned it would be redundant as far as most users are concerned and also might weaken the hook. You cannot fit dummy 3-links to either the hook with loop or hook with type 2 latch because it would prevent the coupler working.
Yes, the DIY magnet illustrated below was designed by Mr Jim Mitchell of ACT, Australia, who uses Dingham Autocouplers on his British outline Gauge O layout.
Jim very kindly sent Trevor Shaw a magnet for testing and gave his permission to reproduce the details here. Jim's DIY magnet is of high resistance (about 18 ohms). It takes a relatively low current ( about 0.7A at 12V DC) so is unlikely to burn out and is also unlikely to burn switch contacts. Electrical supply and switch types similar to those recommended for the Dingham magnet would be suitable for the DIY magnet also.
The exact number of turns in the coil is not critical. You can either wind until the outside diameter is 16mm or until you have used 25g or 1oz of wire.
In Jim's design, the 3/8in nut serves only as a spacer so that the 5/16in bolt projects no more than 20mm from the coils. Jim fixes the magnets to the layout by self-tapping the bolt into a hole drilled through the baseboard.
In 4mm scale, a 5/16 bolt will not fit between the sleepers, so a 3/16 or 1/4in bolt should be substituted. Alternatively, a suitable nail, about the same diameter could be used.
This idea comes from Barry Pickford, late member of Skipton and District Railway Society.
Barry had a home layout with some rather tight curves and ran full length bogie coaches (50 - 60ft). This makes life difficult for Dinghams fixed to the coupler slot in the coach headstocks but he successfully overcame the problem by “cantilevering” the coupler from the bogies, as shown in the diagram alongside.
Fixed this way, the couplers follow the centre line of the track on curves.
All Dingham products originate from my own modelling needs. If I need something that's not already available, I try to develop it. For this reason, new products are few and far between because I've no ambition to duplicate what's already out there.
In 1999, Skipton & District Railway Society my local club was in need of an improved automatic coupler for its Gauge 0 exhibition layout, Lofthouse in Nidderdale. That resulted in the development of the Dingham Autocoupler for Gauge 0, which first went on sale in February 2000. The coupler is now used on many Gauge 0 home and exhibition layouts. Later in 2000, in response to requests from customers, Electromagnets for remote actuation of the couplers were introduced, The 4mm Autocouplerwas introduced July 2002. It has been adopted not only by 00 and EM modellers, but also by those who aspire to the more exact P4/S4 standards.
The CAD-based Dingham etches are designed to minimise preparation time. Holes are etched accurately so that hardly any opening out with drills or broaches is required. Tabs holding components to the etch are as small as possible, so they can easily be cut without fear of damaging delicate components. Tabs are also carefully placed so that the “pips” can easily be removed with a file.
Instructions are carefully thought out and well illustrated. They are tested by “typical” modellers making up the test etches. Even the packing has been given some thought and masking tape rather than cellulose tape is used, to eliminate the tiresome job of cleaning adhesive residues from metal parts after unpacking.
Each 7mm kit contains parts for 20 vehicles with “normal” buffer lengths, i.e. 10.5mm (most wagons) or 12.5mm (most coaches and locos). These parts can also be used on vehicles with buffers longer than 12.5mm. In addition, there are parts to equip a further 4 vehicles with shorter than normal buffers, such as dumb buffered wagons and some industrial locos.