Under track magnetic uncoupling

[Lemosteam]

Recent threads and an inquiry to @bbussey (credit for the idea here) prompted me to try his concept myself as I will be needing some for my logging module. It interested me because I want rustic sand ballast and no obstructions in the track.

I found some 3/4" X 3/8" X 3/32" thick N42 magnets here:

https://www.kjmagnetics.com/proddetail.asp?prod=BC601

Did some coupler testing and took some photos of how I made these into a single 1.5" long X 3/4" wide X 1/16" thick uncoupling magnet. I was also concerned about too short of an uncoupling zone to use which is why I chose the length I did.

Note use only a sliding motion to separate these magnets. ANY upward lift will snap the in half! Don't ask me how I know...

First I arranged the magnets on a flat surface so they attracted at their edges to align the poles to work for each respective rail. Once you can get all four magnet edges to attract, the poles will be correct.



Next I cut a strips off 0.030" thick styrene sheet and the cut 1.5" lengths off of that.




Adhesive is added to the top side of the magnets.



Then the styrene rectangles are secured to the magnets.



The next sequence of pics is the magnet trapped directly under the track. My hope was that the thinner N42 magnets would not have as much attraction to the trip pin as the thicker magnets would and therefore would not have to recess them any more than the overall thickness of the magnets and styrene.  Of course, one could recess the magnet farther down to make the attraction more subtle.



As the truck mounted couplers from an original Kadee hopper pass over the magnet the coupler performs exactly as expected at both ends.







I'm excited, I finally determined how to do this cheaply and effectively, and am very happy with the results.

[mark.hinds]

I'm probably missing something here, but what's wrong with using the standard Micro-Trains under-track magnets (#308 https://www.micro-trains.com/index.php?_route_=tools-amp-accessories/magne-matic-uncouplers/n-scale-permanent-magnet-under-track-308-1-ea-98800171)?  They have about the same footprint, and I mount mine just under the ties. 

Does your solution deliver a stronger magnetic field?  For magnetic uncoupling, stronger is better, in my experience.  This is because coupler operating behavior varies between different coupler installations (one example being the Micro-Trains couplers that come with Intermountain F-units, which are typically "stiffer" than those on my Micro-Trains 40-foot box cars and reefers.  For automatic uncoupling to be worth it, it has to be absolutely reliable, and this is difficult to achieve, which is IMHO why most people don't use it. 

MH

[bbussey]

The K&J magnets are much stronger than the MTL magnets and I've found that all the current brands/styles of magnetic couplers work reliably and equally well.  I've also found that you can bury 1" x 1/2" x 1/16" K&J magnets into the cork 1/8" down next to the track on either side, covered with a 1" x 1/2" x .060" piece of styrene, and it works equally well as having magnets underneath the track.

[Lemosteam]

Yep, unfortunately, my roadbed is already only 1/4" thick, and I don't want to rout half the material away to get a 1/16" magnet 1/16" below the track, and this cost a total of ~$2.50  with the styrene vs ~$7+, thats all.

[mark.hinds]

Yep, unfortunately, my roadbed is already only 1/4" thick, and I don't want to rout half the material away to get a 1/16" magnet 1/16" below the track, and this cost a total of ~$2.50  with the styrene vs ~$7+, thats all.

OK; thanks.  I've been mounting my MT #308 magnets by cutting completely through my 1/2" plywood sub-roadbed, and shimming back up to the correct height to just touch the plastic ties.  (See reply #44 at https://www.therailwire.net/forum/index.php?topic=28831.msg305681#msg305681 ).  This worked fine in my yard scene, but I recently realized that it might adversely affect the structural integrity of my other scenes, which use "ribbons" of 1/2" plywood under the track.  Your thinner magnets might help me out there, especially if they are less than 1/8" thick, as they could replace a short section of the cork roadbed, and might not require any additional cutting / routing of the plywood sub-roadbed at all. 

The K&J magnets are much stronger than the MTL magnets and I've found that all the current brands/styles of magnetic couplers work reliably and equally well. 
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That's good to hear.  My experience is that many non-MT magnetic couplers (e.g. Atlas PS-1s) do NOT work well enough with the MT #308s, even when mounted directly under the ties, as depicted in my link above.  Stronger is better for magnetic uncoupling.  (Note that I do not use ferromagnetic wheels on my freight and passenger cars, and even #308s will excessively attract the stock wheels on many cars). 

MH

[Lemosteam]

"Strength" is relative of course. 

I tested some 1/16" thick N52 magnets that I had lying about and the attraction was so strong that the hopper was being lifted on the far end, being pivoted about the first axle.     Definitely not what I wanted to see, which is why Bryan lowered his to reduce the attraction.

I also did not want to play with air gap as a dimensional factor, which is why I chose the weaker, thinner magnet to be directly under the track.

I will be laying C55 directly atop my birch 1/4 plywood with no cork at all.  this way i simply use a small laminate router (or Dremel with the router attachment) with a straight bit set at a generous 1/16" depth and put in a nice flat pocket for these to be glued into and not be proud of the plywood.

[bbussey]

Glad to see you found a workable solution for thinner roadbed/foundation scenarios.