Patent ID: 7258513

Claim:
A depth limiting device for generating a hole in a workpiece, enabling precise seating of a countersink insert having a countersink portion within said hole at a precise desired depth, comprising: a stop collar comprising a shell having an open end portion and a workpiece engaging portion extending along the open end portion thereof for contacting a workpiece; a spindle extending axially through the shell, the spindle including a first end extending from the exterior of the stop collar for attachment to a hole forming apparatus, and a second end interior to the stop collar having a centrally located hole forming bit retaining portion having an integral countersink portion for precisely receiving the hole forming bit therein in a fixed depth limiting position, wherein the attached hole forming bit projects through the open end portion of the stop collar at a predetermined length corresponding to the desired depth of the hole in the workpiece to enable insertion of the countersink insert precisely matched to the hole therein; and isolating means operatively associated with the stop collar for isolating rotation of the stop collar from the spindle, said isolating means comprising a rotatable annular carriage body and a bearing assembly contained within the annular carriage body for preventing the spindle from moving axially within the stop collar during operation of the hole forming apparatus, and for isolating the rotation of the spindle from the stop collar whereby the stop collar ceases to rotate when contacting the workpiece without generating sufficient frictional contact to mar or otherwise damage the workpiece.