Kind of a simple tool but, as a beginner it helps me a lot. Since I make a lot of dumb mistakes I like to do air tests before I cut anything. But rather than raising my tool up a a bit and setting Z zero before running my gcode, I insert this fake tool to get a better idea of where I screwed up. It is just a Q-tip (fuzzy end clipped off) with a piece of painters tape on one end (so it fits my 1/8 inch collet better) and a piece of adhesive copper tape on the other. I had the tape in my electronics lab which I use to creat a conductive surface on non-conductive parts - such as to make a pressure sensor. But you might glue a bit of aluminum on the dummy tool instead.
The beauty of this thing is that I can use my probe with it to set Z zero. I only loosely chuck it in the collet so that it will slide up when the machine plunges down for a cut. I can put little Sharpy marks on it to see that it moves and even measure the depth of plunge. When I ram into a clamp ( as I did yesterday) the thing just bends. If I ruin it, I can make another one in less than a minute.
