I have a 15x15 cm heating resistor from my current printer (printing area: 12x12 cm).
I would like to switch to a glass bed and to rework my printer to increase the printing area to 20 cm (22x22 cm glass plate).
Would it be possible to use the old heating resistor placed only in the centre? this way I would have a smaller heated bed for ABS and a bigger one for PLA.
Would the glass crack due to non uniform heating? This is because glass has a conductivity of less than 5 W/mK, therefore the hot area will stay hot and basically never really spread the heat to the surrounding area. So the frame will be cold and the center hot, causing stresses.