Can you machine polish glass?
If you mean to polish out scratches, it can be done, but is generally not worth doing. It requires special and expensive products to do it, which are generally only used by jewellers and people rectifying antique glass.
This makes it expensive, and the results are generally not all that good. You can remove a scratch or even a light chip, but you create a distortion in the glass making a fish-eye lens effect.
It is generally better to replace the glass, even though this can be expensive, you will at least completely rectified the problem rather than just trading it for another.