It might be heat shock. If you're starting with a really cold piece of glass and suddenly warming it unevenly with resistance wire that's embedded in the sub-plate, you could be setting up thermal stresses that the glass can't handle. You might try warming it gently with a heat gun set on low before turning it on.
Andrew Werby
www.computersculpture.com
Qidi X Plus 3 Paper thin first...
Yesterday, 01:15 AM in General 3D Printing Discussion