Cut Square Crosscuts With a Circular Saw Using a Shop-Made Guide From Scrap 1x4

The Problem

A circular saw crosscut freehand is square for about the first two inches. After that the blade follows the operator, not the line, and on a wide board the far edge finishes several millimetres off — enough that the joint shows.

Guiding the cut off a speed square fixes the squareness but not the length: a speed square only reaches across a 2x, so on anything wider you have to slide it and pick up the cut again. And a plain straightedge clamped to the board is only as square as your setting of it, which means measuring and checking every single time.

The Technique

The jig combines both — a long fence for the saw to ride, and a shorter one underneath that registers against the edge of the board so the whole thing lands square without measuring.

1. Take two pieces of scrap 1x4. One is the rail the saw base rides against, and it wants to be longer than the widest board you'll cut. The other is the fence, a shorter piece that will hook over the near edge of the workpiece.
2. Screw the fence across the underside of the rail at 90°, so the two form a figure-4 with the fence projecting below. Check that angle carefully with a square — every cut the jig makes inherits it.
3. Sit the jig on a piece of scrap with the fence hooked against its edge, and run the saw down the rail to trim off the overhang. The saw now cuts its own reference: the freshly cut edge of the jig's base is the blade line.
4. To use it, mark your cut, set the jig so its trimmed edge sits right on the mark, and hook the fence over the board's edge.
5. Clamp it, hold the saw base tight against the rail, and cut.