Constructing a circle with steel rod requires specialised tools designed to create an even roll on thicker metal materials. Using improper methods to create the steel rod circle will lead to an uneven circle. Uneven rolled circles cause problems when you need a circle to fit a specific opening or object. Performing correct math will ensure the size of the circle finishes at the correct diameter and the ends of the circle meet tightly together.

Enter the diameter of the required steel rod circle into a calculator. Multiple the diameter entered in the calculator by 3.142. Subtract the whole number in front of the decimal point and multiply the remainder by 16 to convert the decimal to 16ths of an inch. For example, a diameter of 6 inches multiplied by 3.142 equals 18.852. Subtract the whole number -- 18. Multiply .852 by 16 for a 13.63, or 7/8 inch.

Pull a tape measure along a length of steel rod. Mark the length you determined earlier on the surface of the steel rod with soapstone.

Cut the steel rod to length by sawing the rod at the soapstone mark with a hacksaw.

Push one end of the cut steel rod in between the top holding roll and the lower-front pinch roll of a sheet-metal roll. Turn the pinch-roll height-adjustment knob until the end of the rod slips in between the two rolls. Turn the rear-bending roll knob until the rear-bending roll sits in line with the top of the lower pinch roll.

Turn the roll handle clockwise to send the steel rod through the roll. Raise the height of the rear-bending roll to curve the steel rod. Continue sending the steel rod through the roll and raising the rear-bending roll until the two ends of the steel rod touch.

Push up on the release handle located on the left side of the roll. Push the pinch-roll lifting handle toward the ground. Slide the steel rod circle out of the sheet-metal roll.

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Weld the ends of the steel rod to strengthen the circle.