Back in July, I shared with the second part in my design of a dummy knuckle coupler for OO gauge rolling stock.  You can find the post here.  Since then the first prints have been through several tests and they performed very well.  In this post I’ll show you the small changes I made to the design and share with you how to get some.

The original design, as shown below, was printed in both Shapeways clear Fine Detail Plastic and the Black Versatile Plastic.  The Black Versatile Plastic turned out to be so good I’ve carried on with only this material.  Not only is it strong, but as it’s already the right color, they’re ready to use.

The original design was for a dummy knuckle coupling which would work with Kadee couplings as well as each other.

The first issue I had with them, albeit a small one, was with the knuckle section.  As the actual knuckle, unlike the Kadee, doesn’t swing, and it tended to grip on tight curves.  I opened the jaws slightly to allow a bit more movement.  This solved the issue.

The second issue was due to height.  As I’ve said in other posts about couplings, despite there being the NEM standard regarding couplings and height, different manufacturers have positioned their coupling pockets at different heights. Some seem to be high and some low, which leads to the situation of an uncoupling, especially on gradients as the rolling stock crosses the transition from flat to inclined.  My first answer was to offer three different types, as shown below; high, standard and low.

However given there may be a few different lengths, this makes for a large number of different couplings to manage.

A much simpler idea was to make the knuckle 2mm bigger.   By moving the top up by 1mm and the bottom down by 1mm all versions are covered.  The wings either side of the knuckle were also removed as they performed no real purpose.

This new design was 3D printed on sprew in the Black Versatile Plastic.  The sprew helps reduce the cost of the parts.

The Bachmann OO Class 66 has, what I consider, to be a correctly positioned NEM socket, that is, it’s in the middle of all the rolling stock I’ve tested.  The new coupling fits perfectly and doesn’t look too out of place.

Compared to a standard Kadee in another Class 66, the new coupling looks okay, even if it’s a bit deeper.

The two coupled perfectly and as you can see the new coupling sticks up and down by 1mm, ideal if the coupled item of rolling stock has its NEM socket out of place.

This coupling length is based on a Kadee No. 19. which works well for most items, although I found Hornby coaches ended up with a larger gap between them than I liked, so a shorter version will be designed soon.

For now, these are available in packs of 10, 25, 50, and 150 and you can find them using the links below.

OO NEM Dummy Knuckle Coupling (Large) x10

OO NEM Dummy Knuckle Coupling (Large) x25

OO NEM Dummy Knuckle Coupling (Large) x50

OO NEM Dummy Knuckle Coupling (Large) x150

Once the length of a shorter coupling has been finalized, to reduce the gap between Hornby coaches etc, I will share this with you too.  But now it’s back to the drawing board as I have several projects to wrap up which I’ll also share with you in due course.