Some of our players have serious back issues. We began to help them by making our own “magnetic” jacks that can be lifted with a magnetic boule lifter. Our players liked the magnetic jacks, and asked if we could make a magnetic throwing circle, too.
As we experimented with making a magnetic circle, we discovered that a magnet needs to be able to hold a circle from two different directions. When the circle is lying flat on the ground and we drop the magnet down on to it, the magnet needs to grab on to the circle’s top, wide, flat side. Then, as the circle is lifted up off of the ground, the circle’s center of gravity shifts until the circle is hanging free, vertically, below the magnet. At that point, the magnet needs to be able to hold the circle by its narrow edge. As we lift the circle, the magnet needs to be able automatically to shift from holding the circle in the first way to holding it in the second.
We found two designs that could do this.
(1) A nut on a string
We used a short length of string to tie a piece of iron hardware (in this case, a nut) on to the circle. Our magnet grabs the steel nut, and the flexibility of the string allows the circle to hang from the nut in any direction that gravity pulls it.
(2) A steel button
We added a rounded steel button to the edge of the circle.
When the circle is lying flat on the ground, the magnet grabs the top of the button.
Then, as we lift the circle off of the ground, the circle’s center of gravity shifts and the magnet slides across the rounded top of the button and onto the edge of the button, until the circle is hanging from its edge.
To make the button, we went to the hardware store and purchased a 1/4-inch “screw post” (aka “post and screw”) and some steel washers of two different sizes.
We drilled a hole near the edge of the circle, and used the screw post to attach two steel washers to each side of the circle. Because the washers are of different sizes, they create a rounded profile. The edges of the largest washers extend slightly past the edge of the plastic circle, so that when the circle is hanging from the magnet, the magnet is in direct contact with the edge of the washers.