Hole enlargement apparatus

A method of enlarging the diameter of an existing hole in a workpiece for use in conjunction with a conventional large hole cutter of the type having a cylindrical cup having a toothed peripheral rim, a hub axially secured in a bottom portion of the cup, and a pilot bit axially and removably secured through the hub and cup, comprising the following steps:

• replacing the pilot bit with a drill bit replacement shaft having a hub end portion and an opposite disc end portion, said disc end portion having a disc retention means;
• selecting a guide member having a disc portion dimensioned to matingly fit within the existing hole, a rim portion connected to a rear portion of the disc portion adapted to seat on the workpiece around the hole to align and maintain the disc portion in the hole, and a disc center guide opening dimensioned to slidingly accept a shaft the diameter of the pilot bit;
• sliding the selected guide member onto the drill bit replacement shaft;
• then sliding a disc bias means onto the drill bit replacement shaft to bias and maintain the disc portion into the existing hole;
• and then,
• inserting the shaft through and securing the shaft in the hub carrying the toothed cup having the desired diameter of the enlarged hole;
• and then,
• fitting the guide member into the existing hole so that the rim portion seats around the existing hole;
• and finally,
• applying forward rotational thrust to the drill bit replacement shaft thereby biasing and maintaining the guide member in the existing hole and cutting the enlarged hole with the rotating peripheral teeth;
• so that after the enlarged hole is cut through, the guide member is retained on the drill bit replacement shaft.