I also have this machine, I've been working on it for a week now. One thing I have noticed - the RW torque as applied to the supply reel (leftmost) needs to be strong because the take-up reel (rightmost) is highly frictional. The main clutch at the rear must be able to generate high-slip friction. The small square belt I use is 37.5mm diamter x 1.5mm x 1.5mm; a slack belt won't be able to transfer the torque as applied by the motor pulley. Although, I think a 38mm ... 40mm diameter is okay, but *1.2mmx1.2mm* thickness is no good.
