I make quite a few acrylics and I find that if I squirt water into the hole that it keeps the blank cool. Another thing that helps a lot is to hold the vacume hose to the bit so that it is drawering cool air to the bit as it is turning, this helps big time. Back the bit out of the blank very often clearing the debre off it. Extra sharp tools are a must when turning any of the plastics, acrylics. Lastly what I do is to wet sand with water, this does two things, it keeps the blank cool and next it lubricates.
Wayne