I have now taken the plunge to fit all the stock with modified Alex Jackson couplings. My previous post showed pictures of the couplings development and I have now worked out a standard for 3mm scale for myself.
The wire for the hooks is 0.009” spring steel obtained as guitar strings from my local music shop.
I have reduced the tail of the hook to 2mm but left the other dimensions the same as for a 4mm scale coupling. This takes account of the fact that the coupling doesn’t drop as far as it does in 4mm scale
Coupling height is set at 7mm from the top of the rail.
The image below shows how I have adapted the Sprat and Winkle coupling paddle to take the Alex Jackson wire hook.
The paddles are assembled to the base plate and the hook tails folded over to hold them in place, making sure the paddle is free to move up and down.
The assembly is then attached to the centre of the wagon floor.
A loop of 0.33mm brass wire is fitted to the under surface of the headstock and set at the coupling height of 7mm
The wire for the coupling is inserted through the hole in the paddle and soldered in place, using the gauge I showed in my previous post, to get the correct alignment.
Finally I solder a length of soft iron wire [from a paper clip] to the hook wire just in front of the wagon axle making sure it is vertical.
The coupling is now tested after being set to the correct height and making sure it is central in the track. This is done with the gauge shown below.
Note that there are two pins on this gauge, one for 14.2mm gauge and one for the Broad gauge of 21mm.
I have found that some couplings need an extra piece of lead added to the paddle to get the balance right so only one wire drops when passing over the electromagnet uncoupler.
Now to tackle bogies!