Parametric NEM 362 pocket

Introduction

I have several pieces of rolling stock (and the odd locomotive) that have their NEM 363 slot at either a non-standard height or depth relative to the buffers. Quite a few of these are Bachmann vehicles (they seem to be allergic to following standards), but other manufacturers are guilty too. This means that the NEM 362 pocket that is fitted is then not matching the spec.

This pocket can be used to correct for these errors in a couple of ways:

• Shortening or lengthening the NEM 362 box so that it sits the correct distance relative to the vehicle's buffers.
• Extending the NEM 363 “dovetail” vertically up, thus dropping the NEM362 box down to the correct height.

Of course it can also be used as a cheap standard NEM pocket, as the ones you can buy off-the-shelf are very expensive for what they are.

Print

These print nicely on my MK3S+. I used Sunlu PLA+, which seems to be more than strong enough. Some points I learned whlist iterating the design:

• The 0.3mm chamfer on the bottom edge is to counter-act the inevitable elephant's foot. Without this, the bottom will flare out and the dovetail will not push into the slot on the model easily, if at all.
• Ironing helps smooth the top of the bottom edge of the box, which helps the coupling slide in a bit easier.
• 0.1mm layer height is worth it - the smaller layer lines looks better in my opinion, and they don't take very long to print anyway.
• You will need to fettle the bottom of the top edge of the box, as the filament tends to droop down a bit when the printer is bridging over the empty space. I used a square miniature needle file for this - it took about ten seconds per pocket to clean this up.

Adjusting

I've included the Fusion 360 model file is included in case you need to tweak. Some examples of adjustments your can make:

• To produce a really short pocket to fit something with very short distance between the NEM 363 slot and the buffers (e.g. the Rapido Lion or Loriot):
  • Set stemLength to 0.01mm (setting to 0 breaks the extrusion, but 0.01 won't show on the print). This will save 1.5mm.
  • Reduce boxLength to whatever you need*.
  • Cut your coupling's tail back to be the same as what you set boxLength to.
• To produce a pocket for a vehicle that has the NEM 363 slot set too high (e.g. Bachmann MTA):
  • Set heightOffset to the distance you need to drop the pocket down by.

Other tweaks you can make include:

• Reducing slotDepth to reduce the amount of vertical play the coupling has. For example, Kadee NEM couplings have a shank that is 1.5mm deep, so I dropped this a little bit to stop them moving up and down.
• Adjusting tailAngleSpec in case the NEM 363 slot on your model is a bit different. The spec actually calls for 65°, but I found 58° gave me dimensions that matched most manufacturer's pockets.
• Reducing stemWidth and stemBarDepth to make the stem flexible. I don't see the need to do this, as I don't think the stems on RTR NEM pockets actually bend much when in use, but this might be useful to you.

* Note: If you are fitting Kadees, the rule of thumb I follow is to have the the inner face of the knuckle roughly in-line with the buffers heads. This typically means the vehicle can then be reversed through second-radius (438mm) trackwork without buffer-locking. You may need some trial-and-error here though!

Included models

As well as the standard pocket, I've included STLs for each custom box I've printed. As I print more, I'll keep adding them to this listing. The custom STLs are:

• nem362pocket-nem363mount-custom-rapido-loriot. Used when coupling a Rapido Loriot to other rolling stock with couplings set at standard depths.
• nem362pocket-nem363mount-custom-rapido-loriot-lion. Used on both the Lion locomotive and the Rapido Loriot when these two are coupled together. Whilst the Lion's NEM 363 slot is much closer to the buffers than the Loriot's, I found I couldn't shorten the box below 3mm, otherwise the Kadee knuckle would hit the cosmetic coupling and “she won't couple”. So I compensated for this by using 3mm for both vehicles. This means the couplings are offset relative to where the two vehicles meet, but it doesn't matter in a special train like this.
• nem362pocket-nem363mount-custom-rapido-secr-6wheel-brake. Another Rapido vehicle that doesn't use the standard NEM offset depth.

* Note: The custom boxes above are all intended to be used with Kadee #17 couplers.