Watch the power setting trev, Champagne can cavitate and pop the cork if you over cook it
I'd be looking around 50 speed and 10 power for a starting point working down on speed to say 20 before upping the power if the results aren't good enough
Keep your slideways nice and clean when working with glass, it errodes from the surface when engraved and if it mixes with oil can make a nice effective grinding paste

best to keep the air blow on all the time and vac out the machine on a very regular basis
best wishes
Dave