In my role as Publications Officer for the 2mm Scale Association, I'm currently working on a revamp of the "couplings" chapter of the erstwhile 2mm Handbook. I was intrigued by the reference to Lin-Cup couplings, which I hadn't heard of or seen. So I went back to the June 1976 issue of the 2mm Magazine to read Lindsey Little's original article. His goal of "something inconspicuous, not too unrailwaylike, close coupling, sturdy and capable of being made by a squint-eyed tyro with ten thumbs" sounded promising...
I decided to have a go at making some following the instructions in the article. If nothing else, this would allow me to photograph them for the new handbook. Firstly, here is a photo of a completed coupling, glued to the underside of a Buchanan Kits open wagon. The underside of the wagon is a mess because I had to remove the folded-up coupling "boxes" that I had previously fitted before painting. This illustrates a nice feature of the Lin-Cup: the "gubbins" is all hidden behind the solebars, with only a wire hook protruding beneath. Like an Electra, the hook hangs at a 45-degree angle (when the wagon is upright) thanks to the small lead fishing weight behind the pivot. The headstock of the wagon keeps the wire shank horizontal and hence the hook at the correct angle. Unlike the Electra, the pivot is on a 60-degree(-ish) angle to the headstock, so that when another coupling pushes against it, the hook both rotates both down and towards the vertical, allowing the opposing coupling to snap past.
The coupling seems to have been more utilised in 7mm scale, in the form of the "Lincs" auto coupler (see here). But I haven't seen it during my (comparatively recent) involvement in the 2mm scene.
Although I haven't yet tried them in operational use, I think this coupling has several benefits. Firstly, and importantly for me, it is robust and quite forgiving of misalignment. At the same time, it is probably the least conspicuous 2mm auto-coupling other than the fiddly Alex Jackson. Here is a comparison of wagons fitted with Lin-Cups (right) and Electras (left):
It's hard to see here but with the Electras you can actually see the weights hanging down behind the wheels, as well as the pivot tube beneath the headstocks. There is a further advantage to Lin-Cups not visible here: you could still fit dummy representations of real 3-link or screw couplings, hanging down from the coupling hook. This is not true (I don't think) with Electras, where the delay "dropper" would get in the way. (As yet I haven't found the time to try making 3-links, it has to be said.) The next photo is a comparison with DGs, which prevent you even from fitting the coupling hook:
When it comes to operation, the Lin-Cup lacks the "delayed action" facility of DGs, Electras or Alex Jacksons, where you can uncouple at one location and propel the wagons to another spot without coupling up again. But it makes up for this, I think, by (a) the above advantages and (b) the fact that you can uncouple using simple permanent magnets underneath the track. This works because the only way to uncouple is to reverse the train (taking the tension off the hooks) while over a magnet. Similar to the "Electra shuffle". Here you see two wagons as they would look while pushing along clear track (top) and while over a magnet (bottom):
Notice that the couplings hang down quite a long way - this could be limited by putting some packing under the wagon floor to stop the "weight" end behind the pivot from moving up so far. Here are two end views to show how the coupling hook moves when over a magnet. The magnet here is actually fixed (temporarily) below the wooden base of my test track.
So why are these couplings not so popular? Perhaps there is a fatal flaw that I am yet to discover, but I suspect it is partly the fact that they are not commercially available and you have to make them yourself. This turned out not to be too difficult, but it would be very hard without first spending a little time to make jigs like those recommended in the original article. The first is for bending the "frame" and just consists of two bits of nickel silver soldered together. The hardest part was cutting/filing one of these into the shape of an equilateral triangle, which I did by guesstimating. I've been making the frames from 28swg phosphor-bronze which makes it easy to spring onto the tube.
The second jig is for soldering the steel hook to the tube. A jig is essential here as it has to be soldered at a 30 degree angle in one plane (so that it will pivot sideways) and a 45 degree angle in another (so that it will hang at 45 degrees in the resting position). I found a scrap bit of aluminium angle and followed the instructions in the article, drilling and filing a slot to hold the brass tube. It's hard to see but the section of aluminium against which the hook is sitting is bent up at 45 degrees. For the record, my tubes are 0.8mm (O/D) brass from Albion Alloys, which gives a nice free fit over the p/b frame.
I scribed a mark at "5mm in front of the frame" to guide me, but I found that slightly longer is needed for the wagons I've tried so far, because the coupling hook extends through the headstock and prevents the coupling frame from being fitted right up against the inside of the headstock. The hook is made from the same spring-steel wire (or guitar string) used for Electras. In use, I fixed the hook to the jig with masking tape and held the tail end down with a bit of wood. I used Carr's Yellow Label flux and plenty of solder. A decently-sized soldering iron bit was helpful as the aluminium acts like a heat sink. Here's a close up of a finished coupling, once the fishing weight has been "crimped" on and secured with cyano. It's certainly no harder to make than an Electra, and I'm quite impressed so far.