OO Gauge Fixed Link Coach Couplings – Part 2

In last week’s post I shared with you my designs for some 3D printed OO Gauge fixed link couplings specifically for coaches; you can find the post here.  This week I’ll be showing you the actual couplings and some images of them in use.

The initial test prints were done in Shapeways White Strong & Flexible material.  I chose this because it’s the cheapest material they do.  I’ve also used the Strong & Flexible material, instead of my normally prefered Frosted Detail plastics, as these couplings don’t need any fine detail. As they are hidden they simply need to function.  In the image below you can see a set of the white couplings in a pair Bachmann Mark 1 coaches.  This particular set turned out to be too short as the corridor connections meet before the pegs could locate into their holes.

But the good news is I test printed several different sizes in order to see what worked and I was able to come up with a set of 5 which covered all bases.

Below is a set of 40 Type 2 or length 2 couplings.  These are the second shortest type.  This time I 3D printed them in the Black Strong & Flexible material which will also be used for the final couplings.

These couplings were originally developed for use on the beautiful new model of Bournemouth West.  So a good set of coaches to test the new couplings on is Hornby’s British Railways Somerset & Dorset Maunsell coaches, as they would have been common in this station.

In this stock photo below you can see the big gap between the coaches using the standard OO couplings.


However with my coupling fitted, the corridor connections are millimeters apart, as you can see in the images below.  This gives the impression of a joined connection.


And as these coaches are fitted with the NEM cam system, this causes the NEM socket to swing and move out on corners; the gap increases as the coaches travel around corners. This prevents the corridor connections and buffers from locking up and derailing the coaches.

The overall effect is very good.  Also they won’t come uncoupled but can simply be lifted off the layout when done.

These couplings also work well for the Bachmann Mk’1 coaches.

This older set wasn’t fitted with the cam system but my couplings still worked well around the corners, as the NEM socket swivels.

The Hornby Pullman coaches have their NEM couplings set much further back than the others I’ve tested so far and required a longer coupling.  The ones used below are still a bit too long but this has been corrected in my computer model.

Here are some videos of the test couplings in use with a push-pull service reversing around the corner and heading into Bournemouth West Station.

And again with a section of the Bournemouth Belle coming around the corner and heading into Bournemouth West Station.

And finally with the Pines Express; some of these coaches have Kadee couplings but mine have been used on the rest.

Just of interest, the layout Bournemouth West will be making its debut appearance at the Swindon Railway Festival, held at the Swindon Steam Museum on the 9th and 10th September 2017.

Next week I plan to share the couplings with you in their finished condition and also let you know where you can get them.

OO Gauge Fixed Link Coach Couplings – Part 1

At long last my freight couplings for British OO rolling stock with NEM sockets are now available, so it’s time to share with you my designs for coach couplings.  You can find the freight couplings here.

Early British coaches had similar coupling to the freight 3 link.  They each had a hook and a chain, but because passenger stock needs to be smooth, the chains had a screw section in the middle. This worked by having the locomotive push two coaches together so the buffers compressed, then the chain was hooked over the hook and the screw tightened up.  When the locomotive releases the pressure the buffers can never fully un-spring.  This means there’s never any slack which would cause the train to snatch and jerk, as that’s not ideal when you’re sitting down to lunch!  Below is an example of a locomotive coupled to a coach with a screw link coupling.

Later coach stock adopted the knuckle coupler, very similar to the standard system used in the US. The difference is the knuckle can rotate around the hook so both systems could be used.  The knuckle coupler would hang down allowing normal access to the hook.  When needed, the knuckle coupler was lifted and held in place by a pin.  In the picture below you can see this arrangement on a BR Mk 1 coach. (Picture by Chris McKenna from Wikipedia)

The pin also held the knuckle down when not in use to prevent it from swinging.  This has also been implemented on locomotives.  You can see it on the front of the BR Class 91 locomotive below. (Picture by Chris McKenna from Wikipedia).

Modeling this can done and, with newer models now having the NEM sockets, different couplings can easily be exchanged.  A plug-in Kadee knuckle coupler is available for the NEM socket and it’s a good way to connect coaches.  However as with the freight stock, if you have rakes of coaches which you want to stay permanently coupled, adding Kadee couplers comes with the risk of separation plus the expense of adding one to each end of every coach.  Bachmann make a coupling designed to be a fixed link between coaches which looks like vacuum pipes hanging down.  Again this is a good idea but what if you run trains at exhibitions or like to swap the trains on your layout?  Picking up 5 to 10 coaches all linked together is a bit tricky.

So how is 3D printing a coupler better than this?  Well, the nice thing about coach stock is they normally have a corridor connection so travelers can move from coach to coach; this hides the coupling.  Therefore the coupling doesn’t have to represent anything, it simply needs to work.

My coupling is just that, simple.

Each has a peg and hole at one end and the NEM fitting at the other.  The two couplers simply overlap.  The height of the peg ensures they won’t come uncoupled but when you want to remove the coach from the layout you simply pick it up.

As with the freight rolling stock different manufactures have placed their NEM sockets in different locations causing the gap between coaches to vary.  This gap will also need to be specific to your layout depending on the radius of your curves.  So to solve this I have made a few options in length.

And unlike the freight couplings there are only a few; five different types in fact.

They can be used in pairs with the same number or mixed together to give any required length.

Next week I’ll share more with you regarding these couplings and some images of them in use.

Fitting DCC to Wrenn OO Locomotives – Horizontal Motors

This week I’m going to share with you a simple way to add DCC (Digital Command Control) to older Wrenn OO locomotives.

Wrenn locomotives date back to the 1960s but don’t be fooled by their age.  They’re very good models and are still widely collected and run.  If you find one in its original box it may even be worth a lot of money, depending on the model inside.

One of their main advantages is they’re all metal, making them very heavy.  This gives them a lot of tractive effort compared to models produced in later years.  The mechanisms are simple but well-built which means most of them are probably still running well.  However these were all designed well before the concept of DCC came along so the motor wasn’t isolated from the chassis.  In fact one of the motor brushes is connected directly to the chassis which makes converting these to DCC a problem.

But to overcome that problem I’ve come up with a simple way to easily make the conversion.  The Wrenn locomotives I’ve come across have one of two types of motor; horizontal and vertical.  This week I’ll cover the horizontal motor which is in the 8F 2-8-0 as pictured bellow, the Castle 4-6-0 and the Rebuilt West Country 4-6-2 which is the locomotive I shall be working on today.

The Rebuilt West Country has the motor and all the wires located under the shell.

With the shell removed you can see a single black wire, which runs from the right hand wheels, connecting into the green wire and going to the right motor terminal.

The left terminal is connected to the chassis by a metal bolt.  Both terminals are linked by a capacitor which acts as a suppressor to prevent interference with televisions etc.  Each terminal also has a spring which keeps pressure on the motor brushes inside the brush holders.

The brush holder on the right is isolated from the chassis and is only connected to the green wire.  The brush holder on the left is the one which gives us the problem.  In the image below I’ve released the spring and the brush has fallen out.  Be carefull not to drop the brush as they are made from carbon, just like a pencil lead, and can easily crack.

The brush holder is made from brass and is fixed directly into the chassis, making a perfect electrical connection.  The brush holder should pull out with a pair of pliers as I have done below.  If not, it will need to be drilled out; if you have to do this dismantle the whole motor first, because you don’t want to damage the inside or get metal filings in the armature.

With the brush holder removed it’s a simple matter of replacing it with something which works as an insulator.  And the answer is a 3D printed brush holder.

These have been designed to be a direct replacement.  They are 3D printed in Shapeways’ Frosted Ultra Detail material and should fit into the hole with a push.  It’s important to check first that the brush slides freely inside the holder.  Any print residue inside may cause the brush to stick and this will prevent the locomotive from running.  Any residue can be removed with a drill, the same size as the brush, or a round file.  If the brush holder is a loose fit in the hole simply fix it in place with some superglue.  (Superglue is made from acrylic and so is the Shapeways FUD)

The black wire from the right hand side wheels has been cut and will be joined to the DCC decoder.  The capacitor has also been removed.  Under the left motor terminal is a bolt which also connects this side back to the chassis; this needs to be removed and left out.

At this stage a continuity test using a volt meter is a good idea to ensure the two terminals really are isolated from the chassis and both left and right wheels.  If they are, then the brush can be re-fitted and the spring clipped on to hold it in place.  The wires from the DCC decoder can now be soldered to the motor terminals.

The power feeds can now be connected; one goes to the black wire and the other to the chassis.  I connected the chassis wire to the screw holding on the weight at the front of the loco.

And that’s it, the loco is chipped and ready for testing.

Next week I’ll share with you how to isolate a vertical Wrenn motor and where to get the 3D printed brush mounts from.

OO Gauge Fixed Link Couplings – Part 2

Two weeks ago I started telling you about my OO Gauge Fixed Link Couplings, you can find the post here. In this week’s post I’m going to share with you the design and different types I’ll be making available and why.

As the name suggests these are fixed link couplings and can’t be uncoupled.  They’re designed to allow strings of rolling stock to be coupled permanently in sets with the correct-looking couplings.  This is ideal for exhibition layouts or block trains which don’t need to be shunted.

The two basic styles, as pictured below, are Instanter, shown in green and 3 link, shown in red.

The actual style of Instanter or 3 link is purely cosmetic as this simply forms a rigid fixed link between the NEM connection.  Why did I do this instead of leaving the chain links loose?  Well, if the links were loose it would alow the coupling to close up when a locomotive is pushing the rolling stock, but this would mean the loco will be pushing on the buffers. Unlike the real thing this doesn’t work very well on most ready-to-run OO rolling stock and tends to lead to derailment.  Having the chains fused turns the coupling into a drawbar and as it’s centered on the rolling stock it allows long trains to be pushed without any issues. To fuse the chain links I have drawn a bulge making them a bit fatter where the links meet; this causes them to overlap and become one solid piece.

As I said above, making the connection into a solid drawbar gives the advantage of allowing the train to be pushed but what about going around curves?  The NEM sockets do allow a bit of sideways movement but depending on which manufacturer will depend on how much. So I have designed in a flexible section at each end which allows for some more movement.  This can be seen on the Instanter connector below.

As the coupling bends either to the left or right one of the gaps will open slightly.  When the train is being pushed the gaps close equally keeping the force straight.

Below I have two brand new OO Bachmann covered hopper wagons linked with the coupling above.

As the trucks are twisted to the max, where the buffers touch, the NEM socket swivels as well as the flexible section in the coupling.

The different types, apart from Instanter and 3 link, refer to two variations in the NEM sockets.  The first is length, or rather the distance the NEM socket is set back from the front of the rolling stock.  Although the NEM standards specify the size and position of the socket, not all manufacturers have them in the same place. Length is also governed by the tightest radius curve on your layout.  The tighter the radius the further apart the rolling stock needs to be before the buffers lock and cause a derailment.  With some exhibition layouts which only have big radius curves my shortest couplings can be used.

The second is height, some NEM sockets are lower than others.  To solve this I did an in-depth survey of all the main manufactures and determined that the issue could be overcome with three different shapes, which are all shown below.

The top one is simply a straight coupling.  The second is a cranked coupling and the third is a step-up coupling.  Below you can see the same two Bachmann hopper wagons with a straight Instanter fitted.

The Bachmann NEM socket is low and consequently so is the coupling.  By using a step-up coupling it raises the Instanter.

The cranked coupling is designed to be used when connecting rolling stock from different manufactures.  For instance, below are a Hornby and a Bachmann coal wagons.  The Hornby NEM socket is higher than the Bachmann but using a cranked coupling solves the problem.

You many have also noticed the original plastic molded hook is still on the model above the coupling.  My couplings technically are still lower than the real thing but doing it this way means you don’t have to modify your rolling stock if you don’t want to as the new couplings simply plug-in.  I will also be offering an advanced range which raise the couplings to the corrected height but this will require the plastic molded hook to be cut off.

Next week I’ll share with you the full range of my OO Gauge Fixed Link Couplings as well as a way to judge which ones you need.

OO Gauge Fixed Link Couplings – Part 1

As promised in last week’s post, this week will be about 3D printed parts.  And these parts are OO Gauge couplings.

Traditionally OO gauge locomotives and rolling stock in the UK have relied on the hook and bar coupling or tension-lock shown below.  These date back to the Hornby Tri-ang era and although they work well they are rather unsightly and are in no way prototypical.

For many years different manufacturers trimmed and improved the design but there was no getting away from that huge hook and bar; otherwise their locomotives and rolling stock would not couple up to everybody elses.  Also there had to be a lot of gap between the couplings to allow trains to navigate very tight curves.  Starter sets and train sets always come with a tight loop of track and all the manufacturers wanted their trains to go around them.

Naturally exhibition layouts didn’t want this type of coupling and the modelers invented all sorts of ways to close couple and accurately represent the real couplings for their era. Many kits are now available but on older models a bit of cutting and drilling is normally required and this can get a bit tedious and expensive.

More recently the majority of manufactures have now standardised their couplings in that they have added a NEM pocket to the underside of their rolling stock.

A NEM pocket or socket, as pictured below, is a standard pocket which complies to NEM 362.  This stipulates the size and position of the socket.  The intention is that all rolling stock has a NEM socket which allows any type of coupler to be simply plugged in and will be at the right height.

Currently just about all OO stock now comes with a tension-lock coupling plunged into a NEM socket.

This now opens up the possibilities of getting correct couplings for your era.

Real modern UK rollings stock use the Bukeye connector which is the same design as the standard US equipment but this didn’t happen untill recently.  Early rolling stock was coupled by a 3 link chain and hook as shown below.

Each end of the wagon has a cast hook and a 3 link chain.  Therefore each end is universal and either chain could be lifted and dropped over the hook.  This simple method worked well but rolling stock snapped back and forth as the train accelerated and braked. The buffers are sprung as to absorb the impact but as the trains got heavier it became more of a problem so the Instanter coupling was invented.

This new coupling, as shown below, is similar to the 3 link but the central link is a special cast iron shape.

The coupling can still be used as a loose fit coupling or can be rotated to make it a close coupled connection.  To do this the wagon brake is applied and the locomotive pushed up which compresses the buffers.  Then the chain can be put over the hook and the center link easily rotated.  When the locomotive releases the pressure the buffers release but not all the way as the chain is now much shorter and pulls tight.  Because of the rounded shapes at the top of the Instanter it cannot rotate and keeps the link short.  Now the rolling stock is close coupled and will not snap back and forth.  In the drawing below you can see the Instanter in its rotated position with the rounded shapes at the top.

The two horns at the bottom of the Instanter are there to aid the shunter when they want to release or connect the coupling.  Once the locomotive has pushed up and compressed the buffers the shunter uses a shunter’s pole, as shown below, to hook the coupling up and over.  The metal ‘pigs tail’ in the pole hooks onto the horns.  This makes the shunter’s job safer as they don’t need to go between the rolling stock to couple up.

Many modelers are switching over to Kedee couplings, one of the American standard couplers, as they now supply a coupling which fits directly into the NEM pocket.

However these can be fairly expensive and what if you model older stock which would have had an Instanter or 3 link coupling?  Well the answer is a 3D printed couplings.

My design for these has evolved over the last few months and have been tested thoroughly.  Now I have a set which works in a variety of situations and in next week’s post I will tell you all about them and share with you some photos and videos of the real thing.

Adding Draw Bars to Yosemite Valley Railroad Log Cars

Back in 2013 I started drawing my Yosemite Valley Railroad log cars; you can read the original post here.  Since then I’ve built up a nice train of cars, however, I haven’t added couplings to them all.  So in this post I’ll share with you my simple and cheap design to complete the cars.

The original log car design, as pictured below, was intended to be used with Micro-Trains Z scale couplings.  These are compatible with N Scale couplings but are much smaller and look more prototypical.  However, they are very fiddly to assemble and, if you are doing lots of cars, can get rather expensive.  Also, if the coupling is slightly out of vertical alignment it can uncouple when the cars cross any bumps in the track.  As I only run my log cars in a fixed rake and don’t do any switching with them, installing the Z scale couplings on all the cars seemed a bit over the top.

Yosemite Bulk Head Log Car 2

To resolve this I have designed a draw bar to be used with the same mounting point. The Micro-Trains coupling box fixes to the cars with a screw; a pilot hole is printed in the underside of the car chassis to ensure the couplings are fitted in the right place.  My draw bars, as pictured below, are simply dogbone-shaped strips of 3D Printed Nylon.  This material is Shapeways’ White Strong & Flexible and I’ve used this as it’s both strong and cheap to produce.


Pictured below you can see the draw bars next to the log cars for a size comparison.


The draw bars will come in sets of eight on a sprue and can simply be twisted or cut off with a craft knife.


The holes in each end are the right size for a Micro-Trains screw, although you will need to shorten the screw and tap the hole in the car body.  Micro-Trains supply a tap set for this purpose which can be found on their website.  Alternatively I use tiny screws which are just about the right length.  I tend to get these from old CD drives and computer components which I’ve taken apart before throwing out. You will be amazed how many tiny screws you can accumulate like this.

Below you can see one of these screws in the draw bar, as it has a point it will tap the hole as you screw it in.


When the draw bar is fitted to the car the screw doesn’t want to be tight otherwise it won’t allow the draw bar to rotate.  I have fitted the draw bar under the bulk head end of the car, that way if the screw is too long then the excess length will poke up between the bulk head braces and will be hard to see.


The screw does need to be tight enough so when the car is on the rails the draw bar doesn’t drop as you can see below.


For the other end you could use another screw but this means the cars are permanently coupled together.  If you do a lot of exhibitions, like me, then this isn’t very practical.  So I use a short section of wire simply glued into the existing hole.  It needs to be a stiff, solid core wire, not a multi-strand.  This also means all the cars can only be coupled together facing the same way, just like the originals.


This wire then acts as a pin which will fit nicely into the hole in the end of the draw bar to couple the cars.


Lots of cars can be assembled in this way but the first and last car will still need a regular coupling on one end so locomotives and cabooses can be attached.


My test pieces have been printed in white simply because it’s the cheapest colour but these will be available in black as well.

I’m going to assemble a few more cars and run the set at my local club as a test before I release the draw bars for sale.  Logically there’s no reason why these couldn’t be used on any freight cars which have a body mounted coupling so I’ll try that as well and let you know how it works out.