The idea to ‘float’ the fixture is based on the idea that you don’t want to use one part of the belt sander all the time. Instead, we’ll be able to move the fence when we want to use other parts of the sandpaper, thus preserving more of it in the future. I also wanted to be able to take the fixture off very easily. There are times where I have very large surfaces I want to sand off but don’t want to be hindered by a permanent structure. This easily allows me to remove the fixture at any time and put it back in just a couple steps.
The operation is very simple: We don’t press against the fence, we simply use it as an index, allowing us the ability to hold it upright and know when we are at a 90. If you plan on really pushing into the fence, you’ll want to make the walls a lot wider on the edges to support the added stress.