OO Gauge Fixed Link Wagon Couplings Revisit – Part 1

In March of 2017 I first introduced my OO gauge fixed link couplings for UK wagons, you can find the post here, and they developed into a range of couplings to suit both 3 Link and Instanter couplings.  They’ve been doing well but there have been a few issues so a revisit to the design is required.  In this post I’ll be showing you the first steps.

The couplings, as shown below, are designed to fit into NEM standard pockets and form a permanent link between two wagons whilst retaining the look of a 3 Link and Instanter coupling.

And I think they do this very well.

At the time, an important design feature was the ability to add some flexibility onto the coupling to allow it to navigate corners.  I considered the main part of the coupling too stiff and was worried it would pull trucks off the rails on corners.  A solution was achieved through a flexible section; this was covered in the second post which can be found here.  But it’s this flexible section which has caused the issues.  The material used for the couplings is Shapeways’ Smooth Fine Detail but, as you may have read in other posts, it is brittle and the couplings tend to break at the flexible section, especially when handling several wagons joined together off the rails.  They tend to break here as it’s the part of the coupling with the least material.  One thing I also noticed is that the direction of the print also had an effect on the strength.  The original couplings were printed loose and often standing up on end.  This meant each layer of 3D printed material had a small surface area to bond with the last.  Printing the couplings laid down significantly increased this area and therefore the strength.  Since I made the alteration to print the couplings as a group, see the third post here, they’ve all been printed laid down, but they could still benefit from more strength.

As it turns out the couplings do have some flexibility and the required amount of movement is not great so I’m going to try some 3D printed couplings without the flexible section to see how they do.  Below you can see the revised couplings on the right.

The taller couplings had a much larger flexible section and coincidently it was much stronger; it was the flat coupling which broke more than any others.  But I’m going to try them all.

I’m also going to do some experiments with some of the other materials.  Once I have samples in hand I’ll share the results with you.

A Different Material for Gears

For a few weeks I’ve been experimenting with different materials for small gears and in this week’s post I wanted to share with you one of the materials which doesn’t work.

For a while now I’ve been 3D printing replacement gears for a variety of locomotives in Shapeways’ Smooth Fine Detail material (formally known as FUD).  This material has the advantage of being very accurate to the 3D model size; the detail is crisp, which is ideal for small teeth, it’s hard so it wears well, and several gears can be 3D printed in close proximity to each other without actually touching.

The disadvantage of this material is it hardens, which also makes it brittle.  For larger gears this isn’t a problem as the big surface area also adds strength, but with small and tiny gears the teeth tend to break under shock loads such as a locomotive suddenly stopping.  The tiny teeth have no flexibility and crack when overloaded.  The Smooth Fine Detail material is acrylic, or very close to it, and the properties don’t allow for flexibility.

Recently Shapeways’ introduced a new materiel, Multi Jet Fusion Plastic or PA12.  This is a product which comes from Hewlett-Packard and is a nylon plastic.  This sounds ideal for gears as it’s hard, but with a touch of flexibility, meaning the teeth can take a shock impact.  And it comes in dark grey which is nearly black.  Reading the design specifications for this material the level of detail attainable is not as high as the Smooth Fine Detail but I wanted to see how close it was.  So with a set of gears I’ve recently produced for the 009 Society I 3D printed them in both the Smooth Fine Detail and the PA12.

As you can see the PA12 simply doesn’t have the precision of the Smooth Fine Detail. The teeth have rounded as the material has flowed into itself and the gears are all fused to the spindle.  With the Smooth Fine Detail set the teeth are crisp, the same size as the 3D model, and all spin freely on the spindle.  To be fair these gears are particularly small at only 4.3mm in diameter for the larger and 3.4mm for the smaller.  The PA12 may work with some of my larger gears and I’ll give it a go with a later order.

But for now my primary material for gears is still the Smooth Fine Detail.

Alco C-855 N Scale Replacement Lifters

Sometimes trains get damaged, I’m sure it’s happened to most of us at some time.  And there’s always that one point on a model which is more prone to getting damaged than the rest.  On my C-855 shells it’s the lifters at the rear of the model.

The C-855 has four lifting points to allow the whole body to be lifted off the trucks.  There are two in the nose and two at the rear. The nose lifters can be seen below; there’s a recess behind the hole to allow a lifting shackle to be attached.

The rear lifters are raised up on posts.  This is to keep all four lifting points at the same height.  On the real locomotive the posts would have been thick heavy metal but in N Scale acrylic they’re a little thin.  And it’s these that are likely to break if the shell is dropped.

If you can find the broken part it’ll fix right back on with a drop of superglue as this material usually breaks with a clean edge.  Injection moulded parts tend to distort when they break so fixing them back on can be harder.

But if you can’t find the part a replacement is needed so I’ve created a set of four lifting posts as the C-855B has four posts because it has no nose.

The set has two left and two right hand posts and they are all 3D printed on a ring which makes them a single part and therefore cheaper to print.  I’ve made them longer than normal so they can be shortened to the right length depending on where the break is.  As the material is hard these will not cut like injection model plastic but can easily be filed or sanded to get them to the right length.

The replacement C-855 lifters can be found here.

EMD DD35 with Body Mount Couplers – Part 3

Back in January of 2019 I shared with you my test print for an EMD DD35 with body mounted couplers in N Scale.  You can find the post here.  This week I thought you’d like to see what it looks like with a bit of colour.

The shell, as pictured below, is stark white having been 3D printed in Shapeways’ Fine Detail Plastic, also know as FUD (Frosted Ultra Detail).

With the pilots 3D printed as part of the body, the only two parts are the main shell and the fuel tank.  This locomotive will be Southern Pacific 9900.

But, as with most SP locomotives this one won’t stay this clean for long as it’s going to be weathered.

Weathering can be done in many different ways, and to many different levels.  This locomotive will be weathered with enamel paints using an airbrush, and typical for the SP it will bit fairly grubby.

The locomotive will now need a good wheel clean to remove any paint, as it always gets on them, and then it’ll be ready to run.

The DD35 kit with body mounted couplers is available here.

Sad News From The Deeping Model Railway Club

This week I have some sad news from the Deeping Model Railway Club.

For the last twelve years they have held the Stamford Show and this year it was to be on the 18th of May 2019 at the Stamford Welland Academy.  As with most of the shows I attend, and the one I organize for the Poole & District Model Railway Society, most of the traders and larger layouts set up the day before.  Unfortunately in the early hours of the morning the premises was broken into and the layouts and trade stands were destroyed.

The secretary for the Market Deeping Model Railway Club has set up a crowd funding page in which he says:

“Market Deeping Model Railway Club needs your help to rebuild. We have held our annual show in Stamford for the last 12 years. Months of planning goes into the show and years of work goes into building the layout. Imagine our horror and grief when we were greeted by this scene of absolute devastation on the morning of 18th May 2019. Some of the models on display are irreplaceable and whilst money cannot possibly replace the hours of painstaking effort that has been so wantonly destroyed, we would ask that you make a donation, no matter how small, to help us get back on our feet. Please accept our thanks in advance.”

The link to the crowd funding site is below.


Links to news stories in the press:

Deepings Nub news 


The Rutland and Stamford and Mercury 


I hope the The Deeping Model Railway Club can rebuild and recover from this devastating incident.

Choosing The Right Speaker For Your Sound Decoder

This week I have a ‘how to’ post to share with you about speakers and the importance of choosing the right one.

Sometimes I get locomotives in for repair which have been fitted with a DCC sound decoder and the sound simply doesn’t work.  There are several reasons for this and hopefully it’s something simple like a broken wire.  But sometimes the wrong speaker has been used and it’s damaged the decoder beyond repair.

Most manufactures supply speakers with their decoders, but as they often don’t know what you intend to fit it in, the speaker is a generic size, and in N scale this is never going to fit.  There are all sorts of sizes available as well as shapes as you can see below from this selection I had in my bits box.

Two of these speakers are supplied with ESU V4.0 decoders, the smaller speaker comes with the V4.0 Micro.  However, both are fairly large and it can be struggle to find room for them in many locomotives.  So they are often swapped for smaller speakers.  These then become available to be used with other decoders, after all they’re good speakers, but now there’s a potential problem which could damage the decoder, because they may not be compatible.

Speakers are measured in wattage, this is how much power they can handle, and impedance, which is the property of a speaker that restricts the flow of electrical current through it.  This is measured in Ohms.  If you put too many watts through a speaker, you normally just blow the speaker.  But if the impedance of the speaker is too low then more power is used in the amplifier than sent to the speaker and the amplifier over heats and blows.  The amplifiers on DCC sound decoders are ‘solid state’ which means they are made from electrical components only, no form of valves or vacuum tubes as you used to get in guitar and stereo amplifiers, but given how small the sound decoders are that is not surprising.  But this means there really is no tolerance for getting the impedance wrong.

Some speakers, such as the ones used by ESU with their V4.0 decoders have both values written on the back; 1.5w and 4Ohms.

If this speaker was used with a standard Digitrx, Zimo or Hornby TTS sound decoder it would blow the amplifier right away as these decoders are normally only rated at 8 Ohms.  The lower the Ohm value the more power runs through the amplifier.

All sound decoder manufactures should list, either in the decoder manual or on their website, what the max Ohm value is for their product.  But what if you have a speaker and you don’t know what the Ohm value is?  This can easily be measured with a multi meter which can read Ohms.  Below you can see I have the multi meter set to read up to 200 Ohms and when connected to the ESU speaker it is reading 4.3 Ohms.

So now you can select the right speaker to go with your sound decoder.  But going with the smallest isn’t always the best idea.  Normally the smaller the speaker the quieter it gets and it will have less bass.  One of the best ways to increase the volume and bass, without electric amplification, is to add a chamber to the speaker for the sound to reverberate in.  Putting a speaker inside a locomotive shell will do this naturally as the shell forms a box.  But the shell will not be airtight and as a speaker makes noise by pushing air the increase in sound will be small as the air escapes.  Adding a chamber directly to the speaker is the best way and the ESU speaker I measured earlier has just this.  The speaker clips into the box.  But due to the screw holes in the speaker plate and the wire holes it still isn’t airtight.

Digitrax supply their N Scale speakers with a pull-off strip which leaves a sticky surface around the speaker.  It can then be stuck to the chassis or inside of the shell.  But this doesn’t leave a lot of air for the speaker to push against.

I like to use cell phone speakers for my N scale locomotives as cell phones can be very loud!  Below is a Zimo sound decoder with a 8 Ohm speaker.  When soldering the wires onto your speaker remember that a speaker has a large magnet in it so as the soldering iron gets close make sure to hold the speaker down so it doesn’t jump up and attached itself to the iron.  They tend to get very hold and melt very quickly; don’t ask me how I know this!

In cell phones the speaker normally sits over a cavity and is stuck on to form an airtight box.  This is why some phones sound very loud and appear to have good bass.  I 3D print boxes to go with the speakers in different depths depending on how much room I have to work with.

This particular sound decoder is going into an old Rivarossi Challenger and that has lots of room in the tender so I’ll be using the larger box.

I use superglue to fix the speaker but it’s important not to get any on the actual speaker.  So, using the speaker bag, I put some superglue down and rub the box in it ensuring I get some glue on all sides.

Then I place the box onto the speaker and hold it till the glue sets.  Being superglue this doesn’t take long.

The speaker is now ready to fit into the tender and it will be considerably louder than any of the speakers in the first picture.

The thing to remember is to check the impedance.  Most new decoders now support 8 Ohm speakers, ESU going up to 4 Ohm. But a lot of older decoders, even ESU, may be 32 or even 100 Ohm only.

If anybody is interested in 3D printed speaker enclosures or cell phone speakers please get in touch via the contact page.