 Welcome to the video, Calculating Blank Size for Rolled Sheet Metal. In this video, we'll learn how to calculate the blank size for cylinders in a three-roll pinch roller. A calculator is required for our examples. Calculating Bend Allowances To determine the cut length of a rolled part, we must calculate from the center line, or mean, of the finished product. In the figure to the right, let us assume we wish to roll a quarter-inch carbon steel plate into a six-inch round tube. We would use the formula mean times pi equals cut length to determine our blank size. What would be the mean? First, we need to determine if we wish to obtain the inside or the outside diameter. We would then need to subtract or add from the mean. Let's assume we wish to roll a quarter-inch carbon steel into a six-inch round tube. If the outside diameter, or OD, is to be six inches, the center line diameter would be five and three quarters of an inch. If we use the formula mean times pi equals cut length, then 5.75 times 3.1416 equals 18.06. If the inside diameter, or ID, is to be six inches, the center line diameter would be six and a quarter inches. Using the same formula, mean times pi equals cut length, this turns into 6.25 times 3.1416 equals 19.63. If you did not use the mean, and simply used six inches for the diameter, the cut length would be 18.85 inches. Six times 3.1416 equals 18.85. As you can see, although the calculations for determining the cut length are not difficult, using a center line diameter does make a significant difference as does your choice of having the final diameter be in the inside or on the outside. The formula mean times pi equals cut length will be used for the following review questions. After each question, pause the video and solve the equation on your own. You will need a calculator to determine your answers. First, find the mean and record it as a decimal to only three places. Next, record the answer after multiplying the mean by pi. Question one. Say we wish to roll an eight inch outside diameter with one eighth inch thick sheet metal. What is the cut size? The mean is 7.875 and the answer is 24.740. Question two. We wish to roll a seven inch inside diameter with one 16 inch thick sheet metal. What is the cut size? The mean is 7.062 and the answer is 22.187. Question three. We wish to roll a nine and a half inch outside diameter with three sixteenths inch thick sheet metal. What is the cut size? The mean here is 9.312 and the answer is 29.251. Congratulations. You have completed the video activity calculating blank size for rolled sheet metal.