I posted a how-to thread years ago, but even if it’s still here somewhere, the Photobucket pictures won’t be.
I used these 3/8x 7/8x 2 inch magnets. I broke them in half, but you can use them whole. I’d recommend that.
Heres a simple picture of some of the components.
Pretty simple really, I used 3/8 Evergreen Styrene tube, glued it to a strip of flat styrene as wide as the magnet and as long. You can contact cement that to the magnet. THE MAGNET MOUNTS ON IT’S EDGE, NOT FLAT! They are polarized over the EDGES. Fill the magnet end of the styrene tube about 1/2 inch deep, and put a length of piano wire in it. I coiled that end of the wire, optional. You can see on this one I had to lengthen the piano wire. You want this wire to be flexible.
I use plywood blocks to mount this gizmo to the subroadbed with a sheetrock screw. Drill the screw holes so the screw can turn inside the block.these holes work best near a corner of the block, but far enough from it that the block mounts flat up unser the subroadbed. Don’t tighten real hard art first. Once placed under the track, pivot the block to and fro until the magnet raises and drops freely.
A 7/16 hole is drilled in the center of the block and 7/16 K&S brass tube inserted into it. The magnet-tube is simply dropped into the brass tube.
NOTE! My roadbed and subroadbed add up to 1 1/4 thick; 3/4 thick subroadbed, 1/2 thick homasote roadbed. However thick your roadbed and subroadbed is you have to allow the magnet to drop at least 3/8 below the lifted position.
In resting position: