A while back I made a video of my HP ColorPro pen plotter drawing things with its pens. The pens are very cool, but I recently decided it might be worthwhile to investigate using the plotter to cut things up. Initially I thought that it might be cool to turn it into a laser cutter, but since it's not a gantry-type plotter that would be very difficult to do.
Instead I think I'll outfit it with a simple carbide cutting blade like the professional sign-maker plotters use. I did some measuring of my HP's pens, and have determined that a Mimaki type blade holder will probably be the best fit. The length will be just a hair too long, but I bet I can compensate for that by adjusting the blade tension and letting the spring handle the rest.
A pic from some random ebay seller of the blade holder: it's a cheap plastic Chinese knock-off, but the holder itself is very simple, so it shouldn't matter too much how fancy it is. It's cheap enough that I'll buy one and experiment with it.