Plunge saw

A plunge saw or plunge-cut saw is a type of hand-held circular saw which differs from a regular circular saw in that it can plunge into the material to a predetermined depth during the cut. In other words, the depth-of-cut is not fixed and often can be adjusted to be just slightly over the thickness of the board being cut. This property also allows a plunge saw to cut shallow grooves into the workpiece, if necessary. Compared to traditional hand-held circular saws, plungs saws are said to increase operator safety, as well as allowing for reduced splintering and tear-out.
Plunge saws vs. track saws.
Plunge saws usually come with a track system which lets them slide on a guide rail during operation, allowing the operator to perform long and accurate cuts. For this reason, plunge saws are sometimes called track saws. However, any type of hand-held circular saw with attachments for guide rails can be categorized as a track saw, and this feature can thus also be found on some regular circular saws without the plunge-cut feature.
History.
The German power tool manufacturer Festool introduced the first guide rail in 1962, and patented and released the first plunge-cut saw in 1980.