Use the straightedge ruler and measure the size of the device you want to add to the fiberglass. Transfer the measurement to the fiberglass finish using the Sharpie type black marker and identify the corners by a series of small black dots.
Connect the small black dots with a series of straight lines using the straightedge and marker.
Mask the outside edges of the black lines with the blue masking tape. In other words, lay a round of the masking tape around the outside edge of the black line you just made. Depending on the size of the fiberglass surface, you may want to lay out two rows wide of the making tape around the future opening. The masking tape will aid in keeping any scratches on the surface of the fiberglass to a minimum from the table of the jigsaw.
Install the 5/16-inch drill bit into the drill motor and secure the bit tightly into the chuck. Drill a series of holes to the inside of the black line around the marked opening. These holes will allow the jigsaw blade to enter and exit the cut line.
Install the fine-toothed jigsaw blade into the jigsaw. Make sure the blade is set square to the jigsaw's lower table. Place a couple of runs of the blue masking tape on the underside of the jigsaw's table. This will aid in keeping any scratches away from the fiberglass finish.
Place the blade of the jigsaw into the first drilled hole. Start the saw and slowly push the saw to the next hole by following the black line. Allow the saw to do the cutting; do not force the saw blade through the fiberglass.
Continue cutting out the opening by following the progression of the black marker line and the drilled holes. Allow the waste piece of fiberglass to fall from the new opening and pull out the jigsaw.
Use the fine-toothed mill file and, with downward only strokes, clean up any flawed cuts and dress the edge. Do not pull up on the file when applying pressure against the file and the fiberglass, as upward pressure could cause the fiberglass finish to pull loose and create a ragged edge.
Remove the blue masking tape from the fiberglass surface and inspect the opening. You can dress up any irregularities with the mill file.
Things You Will Need
- Straightedge ruler
- Sharpie type black marker
- Masking tape (blue type)
- 5/16-inch drill bit
- Drill motor
- Fine-toothed fiberglass jigsaw blade
- Fine-toothed mill file
- For cutting round holes, you may want to drill the 5/16-inch holes at the 3, 6 9 and 12 o'clock positions around the marked circle.