The stock belt on my 1340GT did work on both the low and high speed pulleys, unfortunately it immediately started to disintegrate. I have been using the Gates Tri-Power notched belts and they have worked very well, I did find that I needed both a BX24 and BX25 size belts for both pulley ratios (although I currently use mine as a single speed on the low speed speed pulley combination). The stock belt is somewhere in between the two. As there are many variables as to how the belts are sized and sit in the pulley, not all belts are the same exact size, so there is some trial and error until one finds something that works. It has been recommended that link belts may not be the optimum solution in this application, from what I understand they are unidirectional. Fine for saws and drill presses running in a single direction, but not optimal for bidirectional belted machines. I have used the Gates for 3+ years, I have had almost no wear or sheading, they run very smooth and wrap very well around the smaller motor pulley without taking a set.
http://www.in-lineindustries.com/education/manuals/accu-link-belt-instructions/
http://www.gates.com/products/autom...d-accessory-belt-drive-system/tri-power-belts
If using a VFD with the stock motor, then I suggest using a single pulley ratio and using the VFD maximum frequency to achieve the same top speed. You can flip the motor pulley, so that the larger motor pulley lines up with the larger headstock pulley. You will need a longer belt. This with running the motor to 90Hz will give you the same top speed as before, no belt changes. If the motor is changed to an inverter type, then one can use a 2.5-2.7" motor pulley and run the motor to 120Hz, which is what I do.
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