Tube Bending Calculator
Work out the degree of bend, wall factor, arc lengths and cut length for a round tube, and get a starting point for mandrel and wiper die selection.
Tube and bend
Results
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– Tooling starting point
Mandrel: –
Wiper die: –
A rule of thumb based on degree of bend and wall factor. Material, ovality and wall-thinning limits and the machine all change the answer. Send us your part print for a tooling recommendation.
Cut length for a multi-bend part
Enter each straight between bends, measured tangent to tangent, and each bend angle. All bends use the centerline radius above.
This is the theoretical length at the tube centerline. Tube stretches slightly during bending, so production cut lengths are usually confirmed with a test bend.
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Save these results as a PDF to share with your team or attach to a quote request.
How the calculator works
Degree of bend is the centerline radius divided by the tube OD. A 3 in CLR on 1.5 in tube is a 2D bend. The smaller the number, the tighter and harder the bend.
Wall factor is the tube OD divided by the wall thickness. Thin-wall tube has a high wall factor and needs more support from the tooling to keep its shape.
Arc length is the length of tube that goes around the bend: radius × angle × π ÷ 180. The calculator works it out at the centerline, the outside of the bend and the inside of the bend.
Outer wall stretch is how much the outside of the bend lengthens compared with the centerline: OD ÷ (2 × CLR). The inside of the bend shortens by the same amount. Higher stretch means more wall thinning on the outside and more risk of wrinkles on the inside.
Degree of bend and wall factor together decide what tooling a bend needs. Read more in our tube bending machine buying guide and bending tooling pages, or work out tube weight with the tube weight calculator. For structural checks, use the section modulus calculator. Have XYZ coordinates from a print? Convert them with the XYZ to YBC converter, and when you know your tooling needs, request a tooling quote.
Frequently Asked Questions
What is the degree of bend (D of bend)?
Degree of bend is the centerline radius divided by the outside diameter of the tube. A 1D bend has a CLR equal to the tube OD and is very tight; bends of 3D and above are generally easier to make.
What is wall factor in tube bending?
Wall factor is the tube OD divided by its wall thickness. A 2 in tube with a 0.065 in wall has a wall factor of about 31. The higher the wall factor, the thinner the wall relative to the diameter and the more likely the tube is to wrinkle or flatten without a mandrel and wiper die.
How do I calculate the cut length of a bent tube?
Add the straight lengths between bends to the centerline arc length of every bend. Each arc length is the CLR × bend angle × π ÷ 180. Because tube stretches a little during bending, confirm production cut lengths with a test part.
When do I need a mandrel to bend tube?
A mandrel supports the inside of the tube at the bend to stop it flattening or wrinkling. It is usually needed for thin-wall tube, tight bends, or both. Thick-wall tube bent on a generous radius can often be bent without one.
What does a wiper die do?
A wiper die sits against the inside of the bend just behind the bend die and stops the tube from wrinkling where it is compressed. It is typically used on thin-wall tube and tight-radius bends.
Does springback change the bend angle?
Yes. Tube springs back slightly after it leaves the bend die, so it has to be bent a little past the target angle. The amount depends on the material, wall and radius. CNC tube benders store springback compensation for each material and part.
Need a bender or tooling for this part?
Tube Form Solutions supplies SOCO CNC tube benders and custom bending tooling, with sales and service from Elkhart, Indiana.