How to Cut an Ellipse in a Metal Roof
In order fit a pipe through a pitched metal roof, you need to cut an elliptical hole in the roof's surface. To visualize the reason for an ellipse-shaped hole needed in the metal roof, rest a section of pipe on a piece of paper and trace the circumference of the pipe onto the paper; as you cut out the traced hole, tilt the paper on an angle and place it over the end of the pipe: You will notice that the pipe does not fit through the round hole, as the hole's length is shortened on a pitch--an elliptical hole has to be cut instead.
Set the outline of the ellipse at the location on the metal surface of the roof where you need to cut the hole.
Trace around the elliptical pattern with the sharp-tipped permanent marker, then remove the pattern from the surface of the metal roof.
Put on the safety glasses and leather work gloves.
Insert the 3/8-inch drill bit into the chuck of the variable speed drill motor, then place the tip of the drill bit on the inside of the marker line you placed on the metal roof.
Drill a hole through the metal roof.
Place an 18-TPI jigsaw blade into the jigsaw, as instructed in the tool's operating manual.
Slide the jigsaw blade into the hole you drilled in the metal roof, and align the cutting edge of the blade with the outline of the ellipse.
Depress the trigger of the jigsaw and push the jigsaw along the marked line to start the cut in the metal roof.
Widen the cut in the metal roof by pulling the jigsaw blade back, twisting it slightly inward and pushing the jigsaw blade forward. This method will allow you to cut around the tight corners of the ellipse.
Run the fine-toothed half-round around the elliptical hole in the metal roof to remove the sharp edges left from the cutting process.
Things You Will Need
- Pattern for ellipse
- Sharp-tipped permanent marker
- Safety glasses
- Leather work gloves
- 3/8-inch drill bit
- 3/8-inch variable speed drill motor
- 18 teeth-per-inch (TPI) jigsaw blade
- Fine-toothed half-round file
- Always keep pressure toward the workpiece when you are cutting with a jigsaw. Without constant pressure, the jigsaw will vibrate and jump, either breaking the jigsaw blade or causing you severe injury.
- When working on a metal roof, do not climb onto the roof while wet with rain or condensation, as the surface of the roof will be extremely slippery.