The barbeque grill has a gentle concave curve inside. The scoop works better for removing ashes if it has a curved front. A radius of about 10 1/2 inches is just right.
The center line marks on the license plate from step 2 are used here to align the plate so the radius can be drawn accurately. I aligned the center line marks with a seam in the table on which I was working. This seam serves to extend the center line so I can use an improvised compass to make an arc on the license plate. Then I used masking tape to secure the license plate on the table. The highest point of the arc is 5 5/8 inches above the bottom edge of the license plate. Mark that near where the center line would run through the license plate. Measure from that point beyond the bottom of the license plate until you arrive at a point on the table seam 10 1/2 inches below the top of the arc. I have placed a piece of masking tape there and marked the center from which the radius for the arc begins. I simply measured and marked a series of short dashes 10 1/2 inches from the center point. Then I made a solid line by hand to define the arc.