[{"data":1,"prerenderedAt":145},["ShallowReactive",2],{"content:guides:bend-allowance-k-factor:en":3},{"slug":4,"category":5,"locale":6,"title":7,"subtitle":8,"metaDescription":9,"intro":10,"sections":13,"designTips":75,"applications":83,"pricingLeadTime":109,"faq":111,"cta":127,"keywords":128,"image":136,"related":140},"bend-allowance-k-factor","guides","en","Bend Allowance and K-Factor Explained","How to calculate flat pattern length for sheet metal bends, with a worked example and typical K-factor values","Bend allowance and K-factor explained with formulas, a worked numeric example and typical values for mild steel, stainless and aluminium sheet.",[11,12],"Bend allowance is the length of material consumed by a bend, and the K-factor is the ratio that locates the neutral axis inside the bend so a flat pattern can be calculated before cutting. Get either wrong and a bent bracket comes out 2-5 mm short or long on its flange, which is the most common rejection cause CutLinq sees on customer-supplied flat patterns.","This page gives the standard formulas, typical K-factor values by material and bend radius, and a worked example so you can check your own flat pattern or your CAD software's unfold before sending a DXF for quoting.",[14,42,65,70],{"heading":15,"paragraphs":16,"table":19,"bullets":41},"The neutral axis and why K-factor exists",[17,18],"When sheet metal bends, the outer surface stretches and the inner surface compresses. Somewhere through the thickness there is a neutral axis that neither stretches nor compresses; K-factor is the position of that axis expressed as a fraction of thickness measured from the inside surface (K = t_neutral \u002F t_total). A K-factor of 0.44 means the neutral axis sits 44% of the way through the material from the inside face.","K-factor is not a fixed material constant. It depends on bend radius relative to thickness, on bend angle, and on the process (air bending versus bottoming or coining), so software defaults are a starting point, not a guarantee.",{"headers":20,"rows":24},[21,22,23],"Inside radius \u002F thickness","Typical K-factor (air bend)","Notes",[25,29,33,37],[26,27,28],"R \u003C 1x t (sharp bend)","0.33-0.38","More material compression",[30,31,32],"R = 1x t to 2x t","0.40-0.44","Most common range for sheet 1-6 mm",[34,35,36],"R = 2x t to 4x t","0.44-0.48","Larger, gentler bends",[38,39,40],"R > 4x t","0.48-0.50","Approaches simple mid-plane assumption",null,{"heading":43,"paragraphs":44,"table":47,"bullets":41},"Formulas: bend allowance and bend deduction",[45,46],"Bend allowance (BA) is the arc length of the neutral axis through the bend: BA = angle_radians x (R + K x t), where R is the inside bend radius, t is thickness and angle is the bend angle in radians (angle_degrees x pi \u002F 180). Flat pattern length = sum of flange lengths (measured to the tangent point) + BA for each bend.","Many CAM systems instead use bend deduction (BD), which is subtracted from the sum of the outside flange dimensions: BD = 2 x (R + t) x tan(angle\u002F2) - BA. Bend deduction is more convenient when flanges are dimensioned to the outside of the part, which is how most drawings are toleranced.",{"headers":48,"rows":52},[49,50,51],"Term","Formula","Used when",[53,57,61],[54,55,56],"Bend allowance (BA)","θ(rad) x (R + K·t)","Flanges measured to bend tangent",[58,59,60],"Bend deduction (BD)","2(R+t)·tan(θ\u002F2) - BA","Flanges measured to outside corner",[62,63,64],"Setback (SB)","(R+t)·tan(θ\u002F2)","Locating the bend line from a corner",{"heading":66,"paragraphs":67,"table":41,"bullets":41},"Worked example: 90° bend in 3 mm S235JR",[68,69],"Part: an L-bracket, 3 mm S235JR, inside radius 3 mm (R = t, a typical air-bend radius), 90° bend, flange legs 40 mm and 60 mm measured to the outside corner.","Step 1: K-factor for R = 1t is about 0.42 (from the table). Step 2: BA = (90 x pi\u002F180) x (3 + 0.42 x 3) = 1.5708 x 4.26 = 6.69 mm. Step 3: BD = 2 x (3+3) x tan(45°) - 6.69 = 12 - 6.69 = 5.31 mm. Step 4: flat length = 40 + 60 - 5.31 = 94.69 mm. Cut the blank at approximately 94.7 mm before bending.",{"heading":71,"paragraphs":72,"table":41,"bullets":41},"Where K-factor tables go wrong",[73,74],"Software default K-factors (commonly 0.44 for all bends) are only accurate near R = 2t. For sharp radii under 1x thickness, using 0.44 overestimates the flat length and the flange comes out short after bending. For stainless steel, which work-hardens more than mild steel, K-factor runs 0.02-0.03 lower than the equivalent mild steel bend at the same radius because the material resists compression on the inside face more.","For critical assemblies, CutLinq recommends bending a first-article sample and adjusting the flat pattern by measurement rather than trusting a single K-factor for the whole range of bends on a part.",[76,77,78,79,80,81,82],"Use inside radius equal to material thickness as a default for mild steel; it gives a predictable K-factor near 0.42-0.44.","For stainless steel, use inside radius of 1.0-1.5x thickness to reduce cracking risk on the outer fiber.","Never specify a bend radius smaller than the material thickness for aluminium 5754 or 6061-T6; it will crack.","Dimension flanges to the outside corner on drawings; it maps directly to bend deduction and avoids ambiguity.","State the K-factor or bend allowance table you used on the drawing if it differs from CutLinq's default, so first-article checks match.","For a part with many different bend radii, request a first-article sample before committing to a production run.","Add ±0.5° angle tolerance and ±0.3 mm flange tolerance as a realistic press brake capability, not a stated zero tolerance.",{"headers":84,"rows":88},[85,86,87],"Industry","Example parts","Typical material",[89,93,97,101,105],[90,91,92],"Sheet metal enclosures","Chassis, covers, brackets","DC01, S235JR 1-3 mm",[94,95,96],"HVAC ductwork","Transition pieces, plenum boxes","Galvanised DX51D 0.6-1.5 mm",[98,99,100],"Machine guarding","Bent panels, access doors","S235JR 1.5-3 mm",[102,103,104],"Signage frames","Cabinet returns, mounting brackets","Aluminium 5754, stainless 304",[106,107,108],"Furniture and fit-out","Legs, brackets, shelving","DC01, 304 stainless 1-2 mm",[110],"Bending cost is driven by the number of bends and setups (each new bend orientation needs a tool change or a re-clamp), by part length (parts over about 2 metres may need a second operator or a special tool), and by tolerance (angle tolerances tighter than ±0.5° require slower, checked bending). A DXF with correct flat pattern and clearly marked bend lines avoids a design review delay; expect laser-cut and bent brackets in 3-5 working days across Egypt, the UAE and Saudi Arabia.",[112,115,118,121,124],{"q":113,"a":114},"Can CutLinq calculate the flat pattern from my 3D model instead of a flat DXF?","Yes, send a STEP file of the bent part and we unfold it using our own K-factor tables rather than trusting the K-factor baked into your CAD software, which reduces first-article mismatches.",{"q":116,"a":117},"Why did my flange come out 2 mm shorter than designed?","This is almost always a K-factor mismatch: your flat pattern assumed a K-factor higher than what the actual bend radius and material produce. Send us the flat DXF plus the intended bend radius so we can check before cutting.",{"q":119,"a":120},"Is K-factor different for stainless steel than mild steel?","Yes, stainless work-hardens more and typically needs a K-factor 0.02-0.03 lower than mild steel at the same radius, meaning slightly more material is consumed by the bend.",{"q":122,"a":123},"What bend radius should I use if I have no preference?","Use an inside radius equal to material thickness for mild steel and aluminium up to 6061-T6, and 1.0-1.5x thickness for stainless steel and harder tempers, to avoid outer-fiber cracking.",{"q":125,"a":126},"Do you provide a K-factor table I can use in my own CAD software?","Yes, ask us for our bend allowance reference table by material and thickness when you submit a design for quoting, so your unfold matches our press brake data.","Upload your flat DXF or bent STEP file, and receive a binding quote within 12 hours.",[129,130,131,132,133,134,135],"bend allowance formula","k-factor sheet metal","flat pattern calculation","bend deduction","press brake tolerance","sheet metal unfold","sheet metal design guide",{"src":137,"alt":7,"width":138,"height":139},"guides\u002Fbend-allowance-k-factor.jpg",1400,933,[141],{"category":142,"slug":143,"title":144},"processes","sheet-metal-bending","Sheet Metal Bending and Forming",1790793880318]