I put in the magnets to hold the lower doors closed. I wanted to do it invisibly so my only choice was to cut a mortise for each magnet from below. The problem is that the magnet must be very close to the surface or there won't be enough pull to hold the doors closed. So the mortise must be cut with one very thin side.
To support the side, I put a caul against the "thin side" to keep from breaking the wood there.
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Then, I chopped the mortise using a 1/8" chisel. The mortises had to be 5/8" deep. The magnets are 1/2" so that's the length of the mortises. This picture shows the mortise finished with a magnet in it. The magnet on the outside is just there to hold the magnet in the mortise forward.
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I used epoxy to glue the magnet in place, and put a plug in the end of the mortise to support the lower part of the mortise (so it didn't break later, in use).
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After the epoxy was cured, I planed the plug down. Since this is the bottom of the door, you won't be able to see the plug.
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I did the same thing on the bottom of the cabinet. This picture just shows the mortises. I plugged them when I did the glue up.
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With that much wood between the magnets, the pull is a lot less than if two magnets were placed face-to-face but it's more than enough to keep the doors closed.
The only thing left is some knobs for the lower doors. I ordered some finger pulls and will install them when I receive them.
Mike