This crosscut jig is a combination of hardboard and plywood. The dimensions are listed in the drawing below, but I recommend leaving the hardboard extra wide to begin with. Use your circular saw to cut the jig to final width.
By using your circular saw to size the hardboard, this creates a reference edge you can use to align your cuts. After marking your layout line on the workpiece it’s a simple matter to make a clean, square cut.
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