Better and Cheaper Magnetic Uncouplers
a.k.a. "Stronger uncoupling magnets"
Yes, you can make your own magnetic uncouplers, and they just might be the most effective uncouplers you'll ever use. In fact, they work so well that you can use them with body-mounted Micro-Trains Nn3/Z couplers. But perhaps the best part is that they cost less than a dollar per uncoupler. All you'll need to buy is Radio Shack #64-1879 (or equivalent) one-inch rectangular ceramic magnets. Two magnets make one uncoupler.
Figure 1: Positioning the magnets
Because they are mounted under the track, it's obviously easier to install these uncouplers before tracklaying. Leave a one-inch gap in the roadbed where an uncoupler will be located. You may need to carve a slight depression in the subroadbed so that the magnets sit flush with the top of the surrounding roadbed. Apply adhesive to the slot (I use Liquid Nails), and place two magnets side-by-side with their long sides together such that they naturally attract and the joint between them follows the track centerline. Then lay the track right over the magnets.
To install an uncoupler in existing track, you'll have to carve out a one-inch slot in the roadbed beneath the track to accommodate the magnets. You may find it easier to remove the ties along with the section of roadbed, then make new ties from scrap ties or strip styrene and bond them to the surface of the magnets with CA before installing them. Apply adhesive to the slot, then slide the magnets sideways into position. Make sure they fit flush against the track.
Since these uncouplers are totally hidden, you'll probably want to mark them so they can be spotted by operators. You could simply paint the ties a slightly lighter or darker color, as if they are very old or just replaced. Or you could place a realistic detail nearby, like a small stack of used ties, a couple of rusted-out barrels, a figure, or any interesting item that's appropriate to find along the track.
In the photo above, I marked the uncoupler with a Preiser figure. Note that the boxcar has a body-mounted Micro-Trains Nn3/Z coupler, while the locomotive has a standard M-T coupler. This is not a mistake; not only can you mix and match couplers, but the uncoupler will properly uncouple and "set" (position for delayed uncoupling) both types. In fact, it is not necessary to maintain strict trip pin height tolerances; I've seen trip pins function properly that were as much as 1/8-inch above the rails.
Sometimes you may not want an uncoupler "live" at all times, such as one that is located on a mainline. In this case you can cut a hole beneath the track and mount the magnets to a block on on a hinge. The uncoupler can then be raised and lowered by a motor drive such as a Tortoise switch machine, or by simply pulling a string!
Figure 2: Installing uncouplers that can be deactivated
IMPORTANT NOTE: These uncouplers may or may not work with Accumate couplers; also, they have not been tested with McHenry couplers.