The usual method of plunge-cutting with a circular saw is to lock in the depth of cut, retract the blade guard and use the leading edge of the baseplate to pivot the saw into the material. That’s how I do it for rough work, but for finish cuts, there’s a better way.
First, loosen the depth lock and raise the blade to maximum height. Now set the base of the saw flat on the work surface, and with the depth lock still disengaged, retract the guard and lower the blade into the work. In this scenario, you’re using the saw’s depth mechanism to make the plunge. If you team up the saw with a straightedge or other guide, precise cuts are possible. What’s more, you can plunge a bevel cut this way, something you can’t do using the other method.
To control the depth of these cuts, which in finish work is not only desirable but also sometimes downright critical, cut a wedge-shaped block from a scrap of 2x. Then drill and countersink a couple of holes through the bottom of your saw’s baseplate in the vicinity of the motor housing. Lock in the desired depth of cut, and slide the block between the base and the motor housing until just snug. Drive a couple of screws to secure the block, and you’ve got your depth stop.
Arne Waldstein, Housatonic, MA