Derek Cohen (in Perth, Australia)
Hi Charles

The glass does not need to be 1m long. That's just the length of the glass plate I have.

My cast iron plates for diamond paste are only 6" long (made from old Stanley planes).

The glass was acquired some years ago for general lapping, including restoring/building planes. The long length does, however, speed up lapping time on blades (less back-and-forth). The down side it that glass can bend/flex, and it becomes essential that it is well supported on a flat surface.

Regards from Perth

Derek