Hi Tom,
I tried exactly the same thing with all sorts of different glues, I think one of the super-glues held out the longest, lasted for a whole 15 minutes 
I have been told by a few people there is a knack to joining the plastic belt, hold a blade in a vice and heat it until it is red hot, slowly slide both ends of the belt over the blade cutting as straight as possible then hold the ends together for a good twenty seconds. I tried and tried and just couldn’t seem to get it but my friend seems to have no problem with it and uses the stuff on a multitude of machines. In the end I bought a leather belt kit from the US e-bay for my watchmakers lathe, it came with glue, instructions and enough belt to do 3 lathes. It works wonderfully and means I wont have to worry about offering sacrificial blades to the gods of belt joining for a long time
Paul.
