A jig for guiding a power tool having a cutter bit to cut joint members in workpieces includes a base frame having a tool support surface and a workpiece support surface. A pair of guide arms are releasably attachable to the power tool. A track is formed on the tool support surface adapted to slidably receive one of the guide arms. A template is releasably securable to the tool support surface having guide surfaces engagable by the other of the guide arms. The track and template co-operate to guide movement of the power tool atop the tool support surface. A clamping system is provided for securing workpieces to the workpiece support surface in a position to be cut by the power tool slidably supported on the tool support surface and guided by the track and the template to provide a joint member in one workpiece and a complementary joint member in another workpiece.