Sheet Metal Bending Calculator
Bend Allowance (BA): BA = Ο Γ (R + KΓT) Γ (A / 180)
Outside Setback (OSSB): OSSB = (R + T) Γ tan(A/2)
Bend Deduction (BD): BD = 2 Γ OSSB - BA
Flat Length: L = A + B - BD
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What is Bend Allowance and Bend Deduction?
When sheet metal is bent, the material stretches on the outside and compresses on the inside. The Bend Allowance (BA) is the length of the neutral axis through the bend β the amount of material consumed by the bend. Bend Deduction (BD) is the amount subtracted from the sum of the flange lengths to determine the flat pattern length.
How to Use This Bending Calculator
- Select material type β Choose from steel, aluminum, stainless, brass, copper, titanium, or polycarbonate
- Enter material thickness β In inches (e.g., 0.074", 0.125", 0.250")
- Set bend angle β 90Β° for standard bends, or any angle from 1Β° to 180Β°
- Specify inside bend radius β Typically matches material thickness for air bending
- Enter flange lengths β The outside dimensions of each leg after bending
- Use material presets or custom K-factor β Recommended presets from industry data
Understanding the Results
- Bend Allowance (BA): Length added at the bend β helps determine flat pattern
- Bend Deduction (BD): Amount subtracted from total flange lengths to get flat length
- Flat Length: The required blank size before bending β critical for accurate fabrication
- Outside Setback (OSSB): Distance from bend tangent to outside mold line
Material Library (Industry Standard Data)
- Mild Steel: K-factor 0.38-0.40, BD at 90Β°: 0.086" to 0.422" depending on thickness
- 304 Stainless: K-factor 0.34-0.38, BD at 90Β°: 0.079" to 0.462"
- 5052 Aluminum: K-factor 0.37-0.48, BD at 90Β°: 0.062" to 0.442"
- G90 Steel: K-factor 0.36-0.40, BD at 90Β°: 0.061" to 0.129"
- Brass/Copper: K-factor 0.33-0.38, softer materials with lower K-factor
K-Factor Explained
The K-factor is the ratio of the neutral axis location to material thickness (K = t/T). It typically ranges from 0.33 for soft materials to 0.5 for very hard materials. Common values: 0.33 for air bending soft materials, 0.38-0.42 for mild steel, 0.45-0.48 for aluminum. For precise results, use our material presets based on real-world manufacturing data.
Why Accurate Bending Calculations Matter
- β Prevents material waste β get the correct flat length first time
- β Reduces trial and error β saves time and scrap material
- β Ensures proper fit β critical for assemblies and tolerances
- β Professional results β matches industry standard formulas
Frequently Asked Questions
- What is the K-factor for mild steel? β Typically 0.38-0.42 for 90Β° bends with air bending.
- How do I find the correct bend radius? β For air bending, inside radius is typically 1Γ material thickness. Our presets use industry standards.
- What's the difference between bend allowance and bend deduction? β BA is material added in the bend; BD is material subtracted from total flange lengths to get flat length.
- Can I use this for aluminum? β Yes, includes 5052 aluminum with appropriate K-factors.
- What units does this use? β US customary units (inches). All results in inches.