Adjustable Miter Guide for Circular Saw

for my next project I need to be able to make reliable repeatable cuts on bigger sheets of plywood so I decided to make a miter box. This one will cut up to 18" wide stock

I used circular saw, drill, clamp, speed square, 2×4", plywood, old door from entertainment centre, 1 1/4" screws and dowel

I had some parts from an old entertainment centre and they tend to stay straight as long as they stay dry. The first thing I did was to make a saw guide using a 3" strip off the entertainment centre door 28" long and screwing it to 1/4" plywood about 32" long. My saw has a 4" offset so I cut the plywood 8" wide so I could cut it straight with the guide. I started with a 24"×24" sheet of 1/2"plywood. I cut a 2x4 11 1/2" long and used my saw guide to cut it down the middle to make 23". I cut a 2" strip from the edge of the door 23" long and screwed it to the cut sides of the (now) 2x2s. I set them upside down to make sure the top was flush, clamped, counter sunk and screwed them together. Don't put a screw near your cut line or you will be making a trip for a new blade. I screwed it down flush to one edge of the plywood and screwed down a 48" long 2x4 flush to the opposite edge. I screwed the saw guide down to the 2x2 making sure to leave enough overhang so that I can swing it to 45° both ways

I used my speed square to set 90° and 45° both ways clamped the saw guide down at each setting and drill a 1/4" hole all the way through then took 2" of 1/4" dowel and glued it into a hole in 1" dowel cut about 1/2" thick to use as a lock peg. Most of my work will be with 1" thick material or less but I built this to be able to handle up to 1 1/2" thick and adjust the sacrificial material as required