I needed one of these for cutting some thin tubes so I made one over the holidays for myself!
I found the idler wheel on an old piece in printing machinery but it's just a .120 wall tube that I added some contour to. The contact wheels are just aluminum bar threaded in the end for a paragon hole saw arbor. The tensioning trolly rides on long shoulder screws that allow belt tensioning with no tools.
The main frame just clamps on the quill like a seat post clamp.
I made it to fit standard hardware store belts and used pieces of material on the shelf so I could see if it works and it does just fine. The low quality belts are sort of a drag and I may have to turn down the contact wheels when I get some decent X backed belts.
29 1028 by frankthewelder, on Flickr
29 1026 by frankthewelder, on Flickr
29 1032 by frankthewelder, on Flickr
29 1033 by frankthewelder, on Flickr
29 1034 by frankthewelder, on Flickr