Welcome Geericks, That's a great project you and son are building. Thanks for sharing, we're anxious for more. Tractor Supply carries flat belt, reinforced rubber seems like it's 12" wide by 1/4"thick. They also have clipper lacing and the vise to install the lacing. My mill uses 4" carriage drive belts and after sitting for a while the surfaces rust a bit causing the belts to grab a little until the rust wears away. Afterwards there's little effort to advance the carriage so I'm wondering about the adjustment /alignment, possibly something binding or maybe a crossed cable from the reel to the carriage...