By using these and a drill press or rig made up of a swamp cooler motor you can cut your own telescope mirror blanks or glass disks for other usages.  Asking $100 for the set.   Sizes they cut are 16", 8" and 12 inch

Also available are 2 very large pieces of 3/4 inch thick plate glass.  The larger piece in front in the photo is on the order of 5 feet by 3 feet in size.