1.Go to a thrift shop
2. Buy a big glass ashtray.
3. Take the ashtray home with you.
4. Break the ashtray.
5. Select the biggest, sharpest shard.
6. Start cutting, being careful not to remove too much.
This technique has been very successful for me in the past. I'm down to a svelte 10X8, and living the female sea cucumbers.