What is the equation for minimum blank size?

What is the equation for minimum blank size?

• A. M = ED + 2(d) + 2mm
• B. M = ED - 2(d) + 2mm
• C. M = ED + d + 2mm
• D. M = ED + 2d

Answer: (A)

When planning a lens blank, you must ensure there is enough material around the finished edge to allow edging, beveling, and mounting. The finished edge diameter (ED) is the size that the lens must ultimately reach. To create a suitable blank, you add material on both sides for the edging process (two times the bevel allowance, represented by 2d) and a small extra buffer (2 mm) for mounting and finishing tolerances. So the correct formula is M = ED + 2d + 2 mm. This ensures the blank has adequate material on all sides for proper shaping and secure mounting. The other options either omit the extra margin, undercount the bevel allowances, or add material on only one side, which would not provide enough space for the necessary finishing steps.

When planning a lens blank, you must ensure there is enough material around the finished edge to allow edging, beveling, and mounting. The finished edge diameter (ED) is the size that the lens must ultimately reach. To create a suitable blank, you add material on both sides for the edging process (two times the bevel allowance, represented by 2d) and a small extra buffer (2 mm) for mounting and finishing tolerances. So the correct formula is M = ED + 2d + 2 mm. This ensures the blank has adequate material on all sides for proper shaping and secure mounting. The other options either omit the extra margin, undercount the bevel allowances, or add material on only one side, which would not provide enough space for the necessary finishing steps.