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Hinged uncoupling magnet for Kadee couplers




The area for the dismantlers (the top level) has a Kadee #308 uncoupling magnet underneath the straighter leg of the turnout. This was the only location where the track was straight enough to get reliable delayed uncoupling. The under-track magnet is much stronger than the between-the-rails magnet, and on a previous layout I found the #308 would interfere with wagons with steel axles. So I decided to try a hinged installation for the new layout, to let me drop the magnet out of the way when it wasn't wanted. Kadee provide the original idea for a hinged installation in their instructions for the #308, so this write-up is my application of their idea.


It is easy to cut away the foam board track bed to make a rectangular hole, much easier than for a plywood track bed and this is a definite advantage of using foam board:



I blanked off the hole with a sheet of 0.030 inch styrene sheet. This makes a surface for ballasting, and is thin enough to not interfere with the operation of the magnet.


The hinge is brass. I have no idea whether a steel hinge (ferrous) would interfere with the magnet, but I'm not keen to find out the hard way. So the hinge is a brass one. I fixed the first hinge onto the intensifier plate with Araldite. This should have worked, but after playing a hot air gun onto the job to make the glue flow, some glue went inside the hinge mechanism and I ended up pulling it apart and cleaning up the intensifier plate with thinners.


I drilled two M2,5 holes in the intensifier plate to line up with my second hinge, and tapped the holes M3. Secured the hinge with two M3 machine screws, set with Loctite 601 and then cut to length and ground flush. This has worked.


By a fluke of good fortune, I could cut one edge of the hole in line with an existing baseboard support. I glued a piece of stripwood onto this support to make a location for the hinge. The hinge is fixed onto the stripwood with small brass screws. The first time I did this, the hinge locked solid. Perplexed, I undid the screws and realised the mounting surface was slightly uneven, and the screws were distorting the hinge out of shape and causing binding. So now, the hinge is shimmed away from the wood with two crinkle washers. This works too.



The magnet seemed reluctant to drop down under the force of gravity, so I glued on 6 grams of lead in a small block. Then I discovered the magnet was sliding on the intensifier plate, and rubbing on the edge of the hole. I fixed the magnet into position with some double-sided sticky tape. So I now had a magnet which would always drop down, and worked well for uncoupling when I held it up.


I added a spare M3 nut onto the intensifier plate with a drop of Araldite. This makes a location to tie on a length of cord to pull the magnet up. The cord passes through a hole in the baseboard frame opposite.


I had a Ratio signal lever to hand and I made a mounting for this on the baseboard. Unfortunately this lever had nowhere near enough throw, so the magnet would not drop far enough to stop interfering with the couplings. So I made a new lever myself:



The lever is a length of mild steel strip from my scrap box. This strip already had a 4 mm hole through its centre. I used a tapered reamer to open up the hole to accept a stack of three M2 plain washers and an M2 crinkle washer. The outer support is scrap of strip brass, drilled and tapped M2 at one end, then a 1.5 mm hole for a pin, then cut to length and given an offset bend. The M2 machine screw is put tight into the brass strip, then passed through the four M2 washers inside the lever and the baseboard frame, and secured with two locknuts and Loctite. The bent piece of brass gives the lever two end stops, and most of 2 inches of throw.


I tried some fine cord to complete the linkage but I couldn't persuade the knots to stay tight, even after putting drops of Superglue onto them. I ended up with a length of 15 lb fishing line. This passes through two screw eyes on its way from the magnet to the lever.


When the magnet is dropped, a coupler above the 'hinge' side still gives a tiny twitch, and it would have been better to hinge the magnet along the short side, across the width of the track. Nevertheless, the whole thing does seem to work reliably. The layout does not have a fascia to fix controls, so the lever had to go in the middle. Most of the lever will be hidden by the landscape, but if I am careful I can leave the bottom accessible from underneath in case I have to put in a new length of fishing line.


This was all rather more long-winded than I expected, but I'm especially pleased with the lever.


- Richard.


  • Informative/Useful 2


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