Get a miterbox like the one in your pic ... looks like my Stanley. Use a knife ... set the black cam clamp in the holes to make a slice of the required thickness.

Slice ... remove slice ... slide the stuff up til it hits the clamp ... Repeat

Bill Drissel Grand Prairie, TX

Get a miter box like the one in your picture. Using a knife set the black cam clamp in the holes to make a slice of the required thickness.

Slice. Remove slice, slide the stuff up until it hits the clamp. Repeat.