Bending Radius Calculator

Welcome to our comprehensive Bending Radius Calculator, an essential tool for engineers, fabricators, and designers working with sheet metal. Accurately calculating bend parameters is crucial for creating precise parts and avoiding material waste. This calculator helps you determine the Bend Allowance (BA) and Bend Deduction (BD), which are fundamental for developing accurate flat patterns for bent components.

Understanding Key Bending Terms

To use this calculator effectively, it's important to understand the terminology used in sheet metal fabrication:

• Material Thickness (T): The gauge or thickness of the sheet metal you are bending.
• Bend Angle (A): The final angle of the bend after the material is formed. For a standard L-shape, this is 90 degrees.
• Inside Bend Radius (IR): The radius of the curve on the inside surface of the bend. This is determined by the tooling (the punch tip) used in the press brake.
• K-Factor (K): A dimensionless value that represents the location of the neutral axis within the material's thickness. The neutral axis is a theoretical line that does not stretch or compress during bending. The K-Factor varies based on material type, thickness, and bending method, but a value of 0.44 is a common starting point for steel.
• Bend Allowance (BA): The length of the arc along the neutral axis. This is the amount of material you must "allow" for the bend itself when creating a flat pattern.
• Bend Deduction (BD): The amount you must subtract from the total length of the outside flange dimensions to get the correct flat pattern length. It compensates for the material stretching during the bend.

Calculate Bend Allowance & Deduction

function calculateBend() { var materialThickness = parseFloat(document.getElementById("materialThickness").value); var bendAngle = parseFloat(document.getElementById("bendAngle").value); var insideRadius = parseFloat(document.getElementById("insideRadius").value); var kFactor = parseFloat(document.getElementById("kFactor").value); var resultDiv = document.getElementById("result"); if (isNaN(materialThickness) || isNaN(bendAngle) || isNaN(insideRadius) || isNaN(kFactor)) { resultDiv.innerHTML = 'Error: Please enter valid numbers in all fields.'; return; } if (materialThickness <= 0 || bendAngle <= 0 || insideRadius < 0 || kFactor <= 0) { resultDiv.innerHTML = 'Error: Values must be positive. Inside Radius can be zero.'; return; } if (bendAngle >= 180) { resultDiv.innerHTML = 'Error: Bend Angle must be less than 180 degrees.'; return; } // Convert bend angle from degrees to radians for JavaScript's Math functions var bendAngleRad = bendAngle * (Math.PI / 180); // Calculate Bend Allowance (BA) // BA = Angle * (IR + K * T) var bendAllowance = bendAngleRad * (insideRadius + (kFactor * materialThickness)); // Calculate Outside Setback (OSSB) // OSSB = tan(Angle / 2) * (IR + T) var outsideSetback = Math.tan(bendAngleRad / 2) * (insideRadius + materialThickness); // Calculate Bend Deduction (BD) // BD = 2 * OSSB – BA var bendDeduction = (2 * outsideSetback) – bendAllowance; resultDiv.innerHTML = '

' + 'Bend Allowance (BA): ' + bendAllowance.toFixed(4) + '' + 'Bend Deduction (BD): ' + bendDeduction.toFixed(4) + '' + 'Units are the same as your input units (e.g., mm or inches).' + '

'; }

How The Formulas Work

The calculations are based on established geometric principles for sheet metal bending:

Bend Allowance Formula:
BA = (π/180) * Angle * (IR + K * T)
This formula calculates the length of the arc at the neutral axis, which is the true length of the material required to form the bend.

Bend Deduction Formula:
BD = (2 * OSSB) - BA where OSSB = tan(Angle/2) * (IR + T)
This formula first finds the "Outside Setback" (OSSB), which is the distance from the corner vertex to the tangent point of the bend on each leg. It then subtracts the Bend Allowance from twice the OSSB to find the total amount the flat pattern must be shortened.

Practical Example

Imagine you need to bend a piece of 2mm thick aluminum sheet to a 90° angle. The tooling you are using creates an Inside Bend Radius of 3mm. For aluminum, a typical K-Factor is 0.41.

1. Enter 2 for Material Thickness.
2. Enter 90 for Bend Angle.
3. Enter 3 for Inside Bend Radius.
4. Enter 0.41 for K-Factor.

The calculator will provide:

• Bend Allowance (BA) ≈ 6.0005. This means the length of material within the bend itself is 6.0005mm.
• Bend Deduction (BD) ≈ 3.9995. If your two outer leg dimensions were, for example, 50mm and 50mm, your flat pattern length would be (50 + 50) – 3.9995 = 96.0005mm.

Frequently Asked Questions (FAQ)

What is a good K-Factor to start with?

The K-Factor is highly dependent on the material, its thickness, and the bending method (e.g., air bending, bottoming, coining). However, here are some common starting points:

• Soft materials (Aluminum, Copper): 0.33 – 0.41
• Mild Steel: 0.42 – 0.45
• Stainless Steel / Harder materials: 0.45 – 0.50

For maximum precision, it's best to perform a test bend on a scrap piece of material and calculate the exact K-Factor for your specific setup.

What is the minimum bend radius?

The minimum bend radius is the smallest radius you can create without the material cracking on the outside of the bend. This limit is primarily determined by the material's ductility. Softer, more ductile materials can handle a "sharp" bend (a small radius, sometimes even 0), while harder, less ductile materials require a larger radius. Always consult the material supplier's datasheet for recommended minimum bend radii.