I wonder what size drive belts bridgeport used on the boss mills?   I'd be shocked to find they are as small as XL's.

On my BTC-1 which is basically a series 1 servo machine, Bridgeport used L sized belts on the X,Y, and Z. Now the Z on this machine is the quill. An L sized belt is massive overkill on the quill. I am doing a conversion on the knee to use Rays method of tool compensation and I will use an L sized belt just because I already have the belts and pulleys.
 I do believe that an XL belt would work fine because of the limited speed of the belt when driving the knee. Power of the motor and the load is only one of the factors involved in belt selection. Speed of the belt drive is a major one and the slower you go the lighter the belt can be. Speed contributes to heating of the belt which degrades the rubber. The other item to consider is the amount of time running at speed. Unless you are build a super high speed machine that will always move at 300 ipm all day long, the belt will spend a fair amount of time just sitting while the other axis move. Hope this helps.


Mike

The belt on my knee drive is an XL, and it works fine, shows no sign of wear, even after using the knee as the Z axis for the last year.

Regards,
Ray L.