Sheet material, even stored flat, can develop a slight bow over time. As it is used for small jobs and pieces are taken out of the material, bowing may become a greater issue, making it difficult to get a good quality engraving. Sometimes you need to flatten the material.
Heavy and flat, yet relatively small, objects can be used to flatten sheet material on the laser table. I use steel bars that were cut to length. You can use a metal saw, welder, or plasma cutter to cut them. The metal bars are available at most hardware stores.
In the photo, you will see two sizes of bars. One is 1?2″ square and the other is 1?4″ X 1 1/2″. The choice allows me to use a size that fits and stays out of the way of the laser’s auto focus plunger.
Image courtesy Bob Hagel, Eagle’s Mark