After I retired, I soon learned that my skill (if I ever had any!) with a circular saw was not very good because I cannot reliably follow a line to cut a board square. To solve this embarrassing problem, I made a simple jig to hold the saw square to the board. Then I found I could never remember the exact dimension I needed to place the jig from the cut so it would be on the correct side of the line!
Step 1: Make a Jig
The jig I made was simply two pieces of wood. The larger piece is a 3/4" x 8" x 12" (approximately). The 8" dimension MUST be as perfectly parallel as possible. The smaller piece is 3/4" x 1 1/2 " x 9". Once cut and smoothed, the smaller piece is attached to the larger piece using glue and screws at EXACTLY right angles to each other as in the picture. In use, the jig is clamped to the board to be cut and the saw base is butted against it resulting in a nice square cut.
Step 2: Where to Clamp the Jig?
But where should the jig be clamped? How far to either side of the line to achieve an accurate length? It was a PITA to try to use my tape each time to get the correct dimension.
To solve this problem, I simply cut into a board part way, stopped the saw, and marked the edges of the base on the board.
Then I measured the distances on either side and the width of the kerf.
Step 3: Mark Your Jig
Then I took the measurements and used a permanent marker to mark the jig as shown in this picture.
Now I can easily set and clamp the jig on either side of the cut and compensate for the kerf to make square and accurate cuts.
I'm also thinking that I could make 2 or 4 accurate blocks that could be placed on the measured line to place the jig without measuring twice but then again, that's a lot of pieces to keep track of.
Always use tools SAFELY! At a minimum, safety glasses and ear plugs/muffs are a must. Take care.
I'm sure there are many ways to do this. Comments are welcome.