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Bending Formulas

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Unfolding Formulas

I was sent several pages of unfolding information last week. Since we do say, “If you have a k-factor chart you would like to share with others, email to me”. Well someone did.

I sat down with all eight pages and reviewed the details. While several pages are dedicated to calculating the Back Gage distance for the press brake, buried throughout each page is the standard formula for Bend Allowance. He probably doesn’t recognize it. But when you check the math, that’s what it is.

I see this a lot. People will tell me they have their own formula and it is different. Yet when you break it down, it is still the standard formula. They may have filled in the Angle as 90 or unknowingly set the k-factor to 1/3, but the formula is the same. Here it is for those who don’t know it.

Bend Allowance = Angle * (PI / 180) * (Radius + K-factor * Thickness)

Remember we have a page with these formulas. Here is a link: Bending Formulas

There are also a few pages to determine the minimum die opening. I found these to be interesting and did not see anything to say they will not work.

What I really liked, was the chart of Bend Deductions. It is a classic. In the title block, it was approved 10-15-35, so you can tell how old it is. It covers 90 degree bends for a number of different thicknesses and radii from 1/32 to ½. Yes, they are shown as fractions. People did not have computers or even calculators back then.

I did take my calculator and reversed the numbers to see what the k-factor was that they used. I was very surprised. It is always in the neighborhood of .5, sometimes bigger and sometimes smaller. But since the bend deductions are written to 3 decimal places, I kind of expected a different range for the k-factor. Well it does say “For Rough Work Only – Accuracy Not Guaranteed”.



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