I’ve used a certain type of circular saw jig to cut straight and accurate lines. All I did was glue and screw a piece of 1×4 to a piece of thin plywood or hardboard. Glue it on a little more than the distance from the edge of the saw base to the blade. When the glue dries, use the circular saw to cut the ply or hardboard to size. Keep the saw tight against the 1×4, using it as a fence. Ne sure the fence is dead straight.
Now when you need a straight line cut with the circular saw, just clamp the edge of the jig at the line and cut away. The fence keeps the blade on the line.
Hope this comes in handy. I can’t take credit for the idea as my dad used to do it back in the 50’s.
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