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# Formula for rod bend length

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 aduetto (Mechanical) 30 May 12 17:12
 Hello,I would like a general formula for calculating the length of a bend in steel (and aluminum?). I know that a precise formula would take into account various properties, but neither me nor my Harbor Freight bender need that level of precision.My immediate project is to bend (e.g. 90 degrees) cold roll rod, probably 3/8" od, to make planter box holders for my wife. I would like to calculate the approximate length of material needed for each piece. I didn't find help in Machinery's Handbook so I turn to you folks. I like to put things in spreadsheets, so this formula would join the sheet metal formula.I realize I could bend some rod, measure it, and life happily every after -- but my spreadsheet would continue to have a gap.Thanks,Alex
 pmover (Mechanical) 30 May 12 19:17
 how many degrees is the bend and what is the bend radius? you should be able to find formulas online to assist you - search arc length, but remember, there is an inner radius and outer radius.hope this helps.-pmover
 StephenA (Civil/Environmental) 31 May 12 8:10
 The length of a 90 degree bend is 90 divided by 360 times Pi times D (= 1/4xPixD) where D is the mean diameter of the bend in the rod.Similarly you can use any number of degrees as a ratio of the total circumference (360 degrees) Stephen ArglesLand & Marinewww.landandmarine.com
 aduetto (Mechanical) 31 May 12 8:38
 Thanks guys! I'll run with this formula.
 MiketheEngineer (Structural) 31 May 12 10:47
 Try one and adjust as necessary - from specs provided above
 IRstuff (Aerospace) 31 May 12 12:27
 Obviously, the accuracy of the equation goes up with bend radius. However, for tight bends, the material is in compression at the inner radius, and in tension at the outer radius.There's a nice discussion about this subject: http://www.condor-rebar.com/news-articles/2011-03-calculating-length-of-bent-bars.html
 aduetto (Mechanical) 31 May 12 14:24
 Thanks IRstuff, I didn't find that one during my Google adventure. I'll also add that one to my spreadsheet as an enhanced formula.
 dgallup (Automotive) 14 Jun 12 9:17
 Most CAD programs will do this for you. They will come with values for the neutral axis Y & K factors for different materials. They will give you a false sense of scientific method and accuracy. The reality is that the result is highly process dependent and most shops have developed their own values from trial and error. Especially error. ---------------------------------------- The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

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