Sven-Olof,
Can you use your belt sander to flatten the back of a chisel? That was my concern. Also, I suppose what I had in mind was a hand-held belt sander which some people clamp in place and then try to work tools on. What you show might be called a linisher, which are quite useful, but again I did not think they would allow the refinement needed for the back of a blade. Is that incorrect in your experience?