Sheet Metal Circle Cutting

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Cutting circles in sheet metal is a fairly easy task as long as you have the proper tools for the job. You can cut a full circle using either a tin snips or a power tool. Curved tin snips can cut circles in a clockwise or counterclockwise direction. Power tools have attachments that guide the tool in cutting out perfect circles.

Things You'll Need

  • Leather work gloves
  • Safety goggles
  • Tape measure
  • Pencil
  • String
  • Scissors
  • Grease pen
  • Large flat screwdriver
  • Hammer
  • Offset compound tin snips
  • Rotozip
  • Circle cutting attachment

Tin Snips

  • Put on leather work gloves and safety goggles. Place the sheet metal across two saw horses, leaving the cutting area in the space between them.

  • Measure the size of the circle to cut with a tape measure. Divide this measurement by two to obtain the radius of the circle.

  • Cut a piece of string 3 inches longer than the radius. Tie one end of the string around a pencil at the bottom, just above the point.

  • Measure the string length from the pencil point to the radius of the circle; grasp the string at this point. Place a grease pen in the hand that's holding the string, without moving your grasp on the string.

  • Set the pencil point down on the sheet metal and turn the other hand holding the string and grease pen 360 degrees to draw a perfect circle for cutting.

  • Place a large flat screwdriver on the grease pen line on the sheet metal so it is at a 90-degree angle to the sheet metal.

  • Hold the screwdriver in place by the shaft and strike it on the handle with a hammer. This will punch a starter hole in the sheet metal.

  • Insert the cutting tip of an offset compound tin snips in the starter hole. Snip in a circle by squeezing the handles together as you would a scissors. Offset tin snips have the handles above the cutting edges to keep your hand above the surface of the sheet metal. This prevents your hands from getting in between the two sharp sides of metal while you are cutting.

  • Cut the circle out following the grease pen markings on the sheet metal.

Power Tool

  • Put on leather work gloves and safety goggles. Place the sheet metal across two saw horses, leaving the cutting area in the space between them.

  • Measure the size of the circle to cut with a tape measure. Divide this measurement by two to obtain the radius of the circle.

  • Cut a piece of string 3 inches longer than the radius. Tie one end of the string around a pencil at the bottom, just above the point.

  • Measure the string length from the pencil point to the radius of the circle; grasp the string at this point. Place a grease pen in the hand holding the string, without moving the grasp on the string.

  • Set the pencil point down on the sheet metal and turn the other hand holding the string and grease pen 360 degrees to draw a perfect circle for cutting.

  • Place a circle-cutting attachment on a Rotozip and turn the thumbscrew clockwise to tighten it in place. A circle-cutting attachment is a long metal arm with a handle on the end to swivel the Rotozip in a perfect circle.

  • Set the Rotozip down on the edge of the grease pen mark for the circle with the knob of the circle-cutting attachment pressing down on the pencil mark in the center of the circle. Turn the speed to “High” for two-speed models, set on “5” for variable-speed models.

  • Hold the Rotozip with one hand and hold the knob of the circle cutter in place with downward pressure with the other hand. Press the bit directly down into the sheet metal to drill a starter hole.

  • Turn the Rotozip clockwise around the circle to follow the grease pen mark while holding the guide stationary in the center of the circle on the sheet metal. The guide will pivot in a circle holding the Rotozip at the same length from the center of the circle.

Tips & Warnings

  • Offset tin snips with a green handle have a curve in them to cut clockwise circles. Red handle offset tin snips cut circles in a counterclockwise direction.
  • Always wear safety glasses or goggles when using power tools.

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References

  • Photo Credit Photos.com/Photos.com/Getty Images
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