Trefoil

I read about the Trefoil long ago (I can't find the article now), and recall that it was invented in the 1960s, but it wasn't until 2004 that I had the equipment to make one of my own. This was my first milling project to use a rotary table, and I found that I needed to do a lot of clamping and unclamping to deal with the four centers of rotation. When I was done, I realized that two stacked rotary tables would have made the job much easier.

I milled my trefoil from 12.7 mm. 6061-T6 aluminum plate. It is rigged in the same manner as the Free-Run mode on the more recent Yates Belay Slave, Baechli, and similar devices. It works, of course, but like all small devices, tends to overheat. The Trefoil tends to rotate so that the standing line slot is vertical, which pushes the carabiner to the side where it tends to trap the rope. If one brakes too hard, the carabiner may shift into a rather low-friction position. I don't have much temptation to make this my primary rappel device, but it is an interesting historical curiosity.