The belt will last for quite a while, but when it starts to slip it's a sign that it's starting to wear out. The slippage you're experiencing is an early indicator that you are heading toward needing a new belt (however it will still run quite a while after it starts slipping). You might want to order one and have it on hand. We can walk you through replacement - it's not too difficult.
Note: It's a good idea to (1) lift the head of the Cimex off the floor when you start up the motor. Also (2) dispense a little solution through the pads while the head is spinning off of the carpet. And (3) start to walk a step forward as you gradually lower the pad gently to the carpet. This will help to take the strain off the belt and help make the belt last longer.
Belt wear is a normal occurrence. It sounds like your belt is closing in on needing to be replaced. Here's what you're looking at, when the time comes...
http://www.excellent-supply.com/Replacement-Belt-for-Cimex-CR48DF-19-inch-Marble-Grinding-Machine-Cimex-Part-40145_p_132.html
Rick Gelinas
