I also created a cutting guide to go along with the cutting grid. The original inspiration for it came from Shop Notes Issue 19, pages 16-19. The same article (slightly expanded) also appears in The Ultimate Jigs & Fixtures Handbook, pages 38-43. The edge of the cutting guide is cut with the circular saw, so you can just line it up and cut. No measuring away from the cut line. This particular cutting guide "captures" the circular saw so that it can only move along the cut and not side to side.

I drew up the parts in Rhino, my new CAD program. Here's what it should look like assembled. Bigger...

Here's what it looks like exploded. The 3-D model is available in Rhino, DWG, DXF, and 3D Studio. The Rhino file is the native file, all of the others are exported. Bigger...

This is a rendering of the assembled Cutting Guide. The 3-D model is available in Rhino, DWG, DXF, and 3D Studio. The Rhino file is the native file, all of the others are exported.

The cutting guide splits into a 5 foot piece and a 4 foot piece. The really cool thing is that you can guide the circular saw with one hand, which is quite useful when cutting across a 4x8 sheet into two 4x4 sheets or two 2x8 sheets. Bigger...

Here's a picture of the cutting grid that I built. Bigger...

Here's a photo of the 5 foot portion of the cutting guide being used to cut a piece off the end of a piece of plywood. Bigger...

This shows the operator's view of the cutting guide. The aluminum angle has some UHMW slippery tape on the inside and the two knobs allow the pressure on the guide to be adjusted. The knob to the rear of the saw holds the saw to the guide (the front portion slides under a permanent lip). Bigger...

Another view, this time from the side. Bigger...