If all the detractors in this thread could stop the self-congratulatory back-slapping (Darwin award references in particular) and actually explain EXACTLY and in detail why this homebrew innovation is so dangerous, I think this argument could be put to bed with much better effect.
I think we can all agree that regardless of whether the tool is made by a manufacturer or an end-user, sharping knives with power equipment is inherently more dangerous than using a hand tool, such as a stone or a strop. Yet Richard J, every time I turn around you are recommending these paper wheels to people without knowing their level of experience with power equipment. Assuming that the knife is being held so that the edge is not leading against the rotation of the wheel, i.e., in a stropping direction, how is it then that the homemade cardboard wheels pose inherently more danger than the wheels your buddy makes and you consistently recommend?
Let's say the homemade wheel isn't perfectly true, well in such a case, which would be immediately apparent before actually using it on a knife, the knife still wouldn't be thrown into your leg and at worse would bounce up and down a little. Let's also imagine that one of the inner laminated cardboard circles becomes delaminated and unbound from the arbor, even then it would just remain stationary while the others spun, more likely posing a fire hazard, if ignored, and not be in danger of hurling the knife across the room. I'm not denying that your friend's cardboard wheels are a superior product, I just haven't read anything in either of these threads that warrants such dire warnings. I'm all ears.