As well as the big 3D printed locomotive shells and parts, I often get asked for small parts and this week I wanted to share with you my design for my smallest yet.  I was asked by a fellow modeller if it would be possible to produce an N Scale Re-Railer to super detail his locomotives.

Re-Railers or Rerail Frogs as they are sometimes called come in all shapes and sizes, typically they are metal castings which are designed to be easy manhandled.  The type I will be looking at is a Y shape with a slot in middle which is designed to straddle the rail.  These are usually carried on locomotives, incase of rolling stock derailment, either on the side of the trucks or slung under the chassis.  They work by straddling the rail next to the derailed train car wheel, then the locomotive either pushes or pulls the car so that the derailed wheel runs up the Re-Railer and back onto the track.  Normally a pair of Re-Railers are used because when one wheel comes of so does the other, the Re-Railers are handed and are designed to work as a pair.

A good photograph of the exact Re-Railer I am modeling can be found here on the translation directory.

Modelling the Re-Railer was not the challenge with this project, that came with the actual size and making it printable at 1:160.  A real Re-Railer is barely 1 Meter (39″) long which in N scale is only 6.25mm (0.24″).  My first draft as shown below was an accurate model of the Re-Railer with some of the details over-sized such as the mounting lugs and flanges to make it printable.

However even with the increased sizes the overall part was still unprintable.  The problem lay with the hole in the mounting lug.  In order to get enough material around the hole to make it printable the lugs became unrealistically large, and if the hole was made any smaller it would also not be printable.  To resolve this I also included the mounting bar and corresponding lugs as shown in the images below; these are normally part of the locomotive.

This solved two problems; firstly, by replacing the holes in the lugs with the bar the thickness of the lugs was no longer a problem, and secondly it would be easy to glue the part, once painted, directly to the underside of a locomotive chassis, as illustrated below on one of my DT6-6-2000 locomotives.

However this design was also unprintable, but not by much.  The black mounting bar shown in the images above is technically a wire by the 3D printers definition of parts.  This means it has to be twice as thick in order to survive the post print process and to guarantee that it will arrive in one piece.  Where the bar protrudes out of the mounting lugs is okay because this is classified as a detail and is supported by the thickness of the lug. I didn’t want to increase the size of the mounting bar as again it would become too unrealistic so as a compromise I filled in half of the area between the bar and the main body of the Re-Railer as shown below.

Given the actual size of the part and that it hangs under the locomotive in shadow this will not be noticeable, especially if the raised part of the bar is painted a different color to the filled-in section.

The test print for the Re-Railer has now been completed and is due for delivery later this week.  In a later post I will share with you how it came out and what it looks like on real model.

Having spent the majority of my N scale modeling time in the American arena I have not kept up-to-date with the British N gauge modeling scene. However I’ve recently become involved with the Poole and District Model Railway Society in England who focus on British N gauge modeling and I now have the opportunity to find out what’s been going on.

The Rapido coupling has been an industry standard for more than 30 years in both N scale and N gauge and in this post I wanted to share with you some of the things that can be done to make your older British rolling stock with Rapido couplers look comparable to the new NEM coupled stock.

The majority of American N scale modelers and manufacturers have moved away from the Rapido coupling in favour of knuckle couplings from companies like Micro-Trains, formally Kadee.   British N gauge modelers and manufacturers are now also moving away from the Rapido and using NEM couplers from companies like Dapol and Graham Farish.

The classic Repido pictured below is a very simple but extremely functional coupler.  It allows trains to navigate very tight corners whilst remaining strong and reliable.

Because Arnold-Rapido, the inventors, allowed the design to be freely copied by other manufacturers it soon became the standard for the scale.  As shown above there are many variants to the design but the fundamental parts are all the same. Up until recently Rapido was the industry standard but now technology has moved on and manufacturers have started to introduce new coupling designs which look like the real thing in size and shape.  Initially the new design of couplers still used the Rapido socket and often new rolling stock would come with Rapido couplings installed with the new design coupling in the box to be installed if required.  Now a lot of manufactures only have their new style of couplers fixed to the rolling stock.  With new British stock even the socket has been updated to the new NEM standard socket although the actual Rapido coupling is still in use.

The biggest immediate difference between Rapido and NEM coupled stock is the gap between them.  Below is a photo of some British N gauge coaches made by Graham Farish,  the red GUV or mail express system coaches behind have the traditional Rapido couplers and the Pullman coaches in the front have the new NEM couplers.

There has to be some gap between the coaches to alow them to navigate corners without becoming buffer locked.  This is when the buffers on the corners of the coach touch each other and prevent the body of the coach from swinging.  With full size trains this is not an issue as the buffers are sprung allowing the buffer to compress and the coach corridor connections to touch.

My first solution is to use my fixed link couplings, pictured below. These fit into the standard Rapido socket on two coaches permanently coupling them together.

By using a shorter fixed link the gap between the coaches is reduced, as shown below.  This is ideal for connecting locomotives together, particularly if they share a DCC decoder as with my E7 DCC conversion, but it is not so good for lots of coaches.

For short trains with three coaches or less this would work well but for longer trains with, say ten coaches, it would be very hard to transport them if they were all coupled together.

My second solution is to 3D print a shorter Rapido coupling. The standard Rapido coupling has a shank length of 3.5mm as shown below.

So I re-drew the Rapido in a range of lengths decreasing by 1/2mm at a time.

Because I wanted these to be cost-effective they have been designed to be printed in the Black Strong And Flexible material offered by Shapeways.  This has three main advantages over the Frosted Ultra Detail material in that it doesn’t need cleaning on arrival, it is already black so they are ready to use right out of the packet and it’s cheaper.  The BS&F material does have a rough finish but this just helps to make them look a bit more realistic.

The first test prints have arrived from Shapeways and have already been successfully tested with Graham Farish coaches.  Although I ordered the full range of sizes all the coaches we tested worked best with the smallest coupler which has a shank length of only 1.5mm. Using a pair of these couplers, one in each coach, it reduced the gap between the coaches by 4mm which in N gauge is a lot.  Below are the same Graham Farish GOV coaches as pictured before but the pair on the left have the new 3D printed Rapido couplers installed.

The difference was considerable but a test on a corner was required to check for buffer lock.  We used one of the tightest corners on the club’s N gauge layout for the test and as you can see below it was successful.

Below is a close up on the original Rapido couplings.

And below is a close up on the new 3D printed short Rapido couplings.  You can see that the buffers don’t actually meet.

We also tested the short couplings on some Graham Farish Suburban coaches with equal success.  Again the short couplings are between the left hand pair.

And a close up of the 3D printed ones.

The 3D printed couplings still need to go through a few more tests and I have also made a few tiny improvements to the design to help with the fit into the Graham Farash coaches.  Once complete I will make them available to buy, and I will also offer them for sale in packs of 20 direct from this site.

One of the tests currently going on is looking to see which length 3D printed couplers work best with an N Gauge HST set, but that will have to wait for another post.