The bend line is the centerline of the bend, that the guillotine brake die should aim at, yes. I was both confused and shocked (by the inaccuracy) the first time I was expected to use the Lockheed tables! The approach I learned was taught to me by a man who fled Germany in 1932 and who's Master's Rating had been gained a couple of years prior to that. They were tabulated by thickness and IML bend radius and never intended to provide accuracy closer than +/- 1/32'nd of an inch. The K-Factor approach dates to WWII and was originally known as Lockheed K-Factors. More sophisticated analysis accounts for these factors. 3 and (B) there is no allowance for the press closing pressure on the stock. Now, the drawbacks to this approach are that (A) the assumption is that the Poisson's Ratio for your materials is closely approximate to. Plugging that into the K-Factor equation gives: K = n/t =. The neutral axis distance from the CL of bend is = t/ln((( r+ t)/ r), where t is the sheetmetal thickness and r is the IML bend radius. 330 looks wrong to me.Ī quick look-up of K-Factor says: K = n/ t, where n is the neutral axis position and t is the sheetmetal thickness. I avoid using a K-Factor whenever possible and I always have to stop and look-up the conversion between it and the more traditional neutral axis shift approach that I learned as an apprentice tool & die maker.
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