Type 3 couplings

This style of coupling is based loosely on the type fitted to many Hudson Hunslet diesels, albeit simplified by making it with a single slot rather than two.

I started with my usual rough sketch, which after making a couple of prototypes ended up being re-drawn in something-angle projection;

(With no apologies to any engineers, real or model, who've stumbled upon this page - I make things rather than worry about proper method.)

With the Unimat 3 set up as a mill and a piece of 6mm dia. brass set up in a dividing head the basic shape can be milled;

To mill the slot I use a .5mm slot drill with the work held in a collet chuck clamped to the saddle;

A .4mm hole, for the coupling pin, is then drilled, but left blind;

The last machining operation is to turn a 1mm dia. locating spigot on the rear and then part-off;

Before each part is parted-off the buffer face needs to be filed to a gentle curve. Here's the almost-finished result;

Now they can be fitted with a pin, .4mm brass wire cyano'd in place with 2mm left protruding.

After much deliberation I've decided to use a coupling height of 6mm for my 006 stock. To set the height for these couplings I first turned a 4.75mm height gauge to mark the centre of the coupling (coupling height minus half the coupling, 1.25mm);

Once a 1mm hole is drilled on the centreline the coupling can be tried in place;

And checked with a second gauge, turned to 6mm;

The finished coupling is a result of quite a lot of work, but to my mind the right coupling can make a loco.

These are destined for 006, for 009 the coupling needs to be lengthened to 3mm.

Paul.