Arch cutting jig

An arch cutting jig for a hand-held saw having a powered blade, a platform for movably supporting the saw on a face of a workpiece being cut by the blade, and a guide holder for attaching an edge guide in fixed relation to the platform for contacting an edge of the workpiece, the jig comprising:

• (a) a trammel arm having a slot formed therethrough and first and second ends, the first end being formed for fixably engaging the guide holder;
• (b) a clamp assembly fixably locatable on the workpiece, the clamp assembly including a frame having a planar face member for contacting the face of the workpiece, an edge member forming an edge surface for contacting the edge of the workpiece and extending in a plane perpendicular to the face member, the clamp assembly defining a pivot axis being aligned with the edge surface and oriented perpendicular to the face when the clamp assembly is fixably located on the workpiece;
• (c) a pivot member rotatably connected to the clamp assembly on the pivot axis, the pivot member projecting from the face member opposite the edge member, the pivot member having a shank portion and a head portion, the pivot member being received by the slot in the trammel arm;
• (d) a fastener threadingly engaging the shank portion of the pivot member for rigidly connecting the pivot member to the trammel arm, the arm being pivotally connected to the clamp assembly on the pivot axis, a spacer element contacting the trammel arm on opposite sides of the pivot axis for spacing the trammel arm above the face member,
• whereby the pivot member is clamped at a desired location along the slot, the saw being guided in an arc concentric with the pivot axis, the pivot axis being at a predetermined distance of zero from the edge of the workpiece, the pivot member being connectable to the trammel arm at a plurality of locations for defining the corresponding radii of the arc.