While working on my Space hulk Terminators, I'm magnetizing their feet so they can be placed on round bases for use in games of 40K. I touched on this briefly in my post about Brother Noctis, but I figured I'd show the process in more detail.
Since every model's feet are space differently, you'll need to make some adjustments when drilling the holes. Ideally, you want to have the magnets in the base set in two of the existing peg holes. If that's not possible, then use one of the holes and an open area. Check the fit on the bottom of the base to see which holes best match with the model's feet.
The rare earth magnets are 1/8-inch in diameter, so use a similarly sized drill bit to drill out the holes. Start by putting a hole in the model's foot and one in the base, through the peg hole.
To put the magnet into the model's foot, apply a dot of super glue to the top magnet in a stack. Press the magnet into the hole, leaving about 1/16 inch protruding.
Hold the magnet in place until the glue sets, then pull the rest of the magnet stack away. I find this method easier than trying to use tools or my fingers to hold the magnet; fingers are too fumbly and the magnet sticks to metal tools.
Drill out the other hole in the base.
To line up the spot to drill in the other foot, place the model on the base with its magnet in the first hole, and position the second foot over the other hole.
Then drill up into the foot through the bottom of the base. If it's difficult to hold the model steady, add a tiny dab of super glue to the feet. Use just enough to hold it in place and allow you to pop it apart when you are finished.
Now you have two perfectly positioned holes in the base and in the model's feet.
Glue the second magnet into the other foot. Then, add your basing material to the base, taking care to keep the holes clear.
To attach the magnets in the base, put them on the model's feet.
Then, stand the model on the base, with the magnets in the holes. Even with the thickness of the sand, the magnets will be at the proper depth to make contact with the model. This method also ensures you won't accidentally glue them with the magnetic poles the wrong way around.
Add some super glue from underneath.
Then fill the holes with some ballast (sand) to give the magnets more surface area to adhere to and prevent them from sliding down.
Once the glue holds on the sand and magnets, pop the model free.
And there you have it– perfectly positioned magnets for interchangeable bases.