A Plastic Screw for an N Scale Con-Cor PA

This week I’d hoped to show you the 3D printed replacement Minitrix Crosshead from last week’s post however due to the heavier than normal snows last night I’ve had no delivery today. So this week I’ll share with you something else which should also be arriving soon.

The venerable Con-Cor Alco PA has been around since 1967 and has been improved over the years but the original design, made by Kato under the name Sekisui, can still be found going strong on many layouts; mine included.  One of the things which made this design different from the later is how the chassis sections are fixed together.  The original design had a solid metal section on the top and two metal sections below, one making contact with each rail through the trucks. Between the top and bottom sections is a strip of plastic for electronic isolation.  It’s all clamped together with screws, metal ones on one side to conduct power from the lower section to the top, and plastic screws on the other to isolate that section.  This works well, but the plastic screws, if removed a lot, can easily be rounded off.  Plus if you drop one into the bottomless depths of an exhibition hall they are very hard to replace.

But thankfully I have a solution.

These have been designed to be 3D printed in Shapeways’ Frosted Ultra Detail material to give the required accuracy for the thread and hardness for the actual screw.

Hopefully these will be delivered soon, along with the other parts, and I will be able to share some photos with you next week.  Plus it will be nice to have my Alco PA back on the tracks.

3D Printed Minitrix Cross Heads

Trix produced a variety of locomotives including a range in N scale, dating back to the 1960s, under the name Minitrix.  Many of these shared common parts and it’s one of these for which I’m creating a replacement; a Minitrix valve gear cross head.

This particular cross head will be for the A4 steam locomotive model shown below.

The cross head is the gray slider which connects the piston and the main connecting rod.  This plastic part slides up and down the metal runner as the piston goes in and out, keeping it level and it also connects the valve gear linkage.

As with a lot of the early plastic parts these can become very brittle and start to break up.  Almost all the other parts of the locomotive’s motion are made from metal, the only exception is the crank pin which drives the eccentric rod.  This is also made from plastic and I’ve previously made this as a replacement 3D printed part; you can read more about that here.   You can identify the crank pin in the first image as it’s gray and not silver, just like the cross head.

The original cross head is a very small part and very difficult to photograph up close so the image below is my 3D model of the part, without any modifications.

The cross head is symmetrical so it can be used on each side of the locomotive.  The box section on top has slots in the sides to allow the slider to pass through. Below the box is a pair of rings, the first connects the cross head to the connecting rod and piston.  As these are joined with a pin the connecting rod is able to rotate as the cross head slides back and forth. The second ring connects to the valve gear linkage, again with a pin allowing it to rotate.

The weak spot on these parts is where the rings connect to the box.  If the valve gear becomes jammed and the wheels keep turning a twisting force is applied at this point. If the plastic has started to break up it will simply snap.

In the image below you can see three cross heads with the original on the left.  The middle one has had the weak area under the box strengthened by adding a larger amount of plastic.  The right hand side one has also had the area between the loops strengthened in the same way and it’s this version which I’m test printing.

This cross head fits most of the British outline steam locomotives including the Gresley A3, A4, Standard 9F, Ivatt 2-6-2 Tank and the Ivatt 2-6-0.  Only the Britannia 7P had a different valve gear with a simplified cross head consisting of a folded metal plate.  Minitrix also made two steam locomotive for the American market, a 4-6-2 K4 and a 2-10-0 Decapod.  As the 2-10-0 shared the same chassis as the 9F this also has the same cross head.  The K4 shared the simpler Britannia 7P chassis.

The part has now been printed by Shapeways and I’m expecting it later this week, and once tested will be made available to buy. It’s often these small, seemingly insignificant parts that aren’t glamorous or even particularly interesting, that 3D printing really comes into its own. The ability to modify, improve and manufacture replacement parts at a fraction of the cost of replacing the locomotive means we can keep the majority of our stock rolling, and it’s why I continue to produce these parts.

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.