Bend Deduction Calculator.
Enter the material thickness, inside radius, bend angle and K factor, plus the two outside flange lengths. The calculator gives the bend deduction and the flat blank length of a part with one bend, in inches or millimeters. It runs in your browser and sends nothing anywhere.
Ordering a bent part? You do not need this: send a STEP of the formed part and we make the flat. Also try the bend allowance calculator.
What bend deduction is.
Most drawings dimension a bent part to its outside corners. Add those two flange lengths and the total is longer than the flat blank you need, because the bend does not use material all the way to a sharp corner. Bend deduction is that difference.
BD = 2 × OSSB − BA with OSSB = tan(A ÷ 2) × (R + T)
OSSB is the outside setback, from the outside corner to where the bend starts, and BA is the bend allowance. The flat blank is the two outside flanges less the deduction: flat = flange 1 + flange 2 − BD.
A worked example
| Input or result | Value |
|---|---|
| Thickness, 16 gauge steel | 0.060″ |
| Inside radius | 0.060″ |
| Bend angle | 90° |
| K factor | 0.44 |
| Outside setback | 0.1200″ |
| Bend allowance | 0.1357″ |
| Bend deduction | 0.1043″ |
| Two 1.000″ outside flanges | flat 1.8957″ |
Measured as straight legs instead, the same part is two 0.880″ legs; the bend allowance calculator gives the same 1.8957″ flat.
Choosing a K factor.
K factor puts the neutral axis inside the thickness, as a fraction from 0 to 0.5. A value of 0.5 would put it dead center; in real bends it sits lower, toward the inside of the bend.
The material, the thickness and how tight the radius is all move it, so no single K factor is right for every part. 0.44 is a common starting value. For an exact number, bend a test strip, measure it and solve the formula for K. Our K factor guide covers the why.
Getting good numbers
- Use the real thickness. 16 gauge steel is 0.0598″, which shops round to 0.060″. Our sheet metal gauge chart lists each gauge.
- Use the inside radius, not the outside one. The inside radius is the outside radius less the thickness.
- Enter the angle bent through. A 90° bend is 90; flanges opening to 135° between them are a 45° bend.
Send the formed part, we make the flat.
You do not have to solve this by hand to order from us. Send a STEP of the finished, formed shape. We produce the flat from that geometry and form it on our TRUMPF TruBend 7036 and 1150 press brakes, so the flat and the bends agree by construction.
The inside radius in your model is a target: the finished radius comes from the closest available tooling for your material and thickness. If a radius is critical, mark it on the drawing so it gets reviewed before we cut.
- Bends up to 96″ long, in 0.020″ to 0.500″ material
- Flange tolerance ±0.030″, bend angle ±1°
- Instant price for bent parts from a STEP file
Common questions
What is bend deduction?
Bend deduction is how much shorter the flat blank is than the two outside flange lengths added together. The formula is BD = 2 × OSSB − BA, where the outside setback OSSB = tan(A ÷ 2) × (R + T) and BA is the bend allowance.
How do I find the flat length from bend deduction?
Add the outside flange lengths and subtract the bend deduction once for each bend. For a 90° bend in 0.060″ steel with a 0.060″ inside radius and K factor 0.44, two 1.000″ flanges give a flat of 2.000″ − 0.1043″ = 1.8957″.
Is the bend deduction the same for every bend?
No. It changes with the material, the thickness, the inside radius and the bend angle, which is why shops keep a value for each tool and material. The finished inside radius comes from the closest available tooling for your material and thickness.
What bend angle do I enter?
The angle the metal is bent through, not the angle left between the flanges. A square 90° bend is 90. A part whose flanges open to 135° between them has a 45° bend.
What K factor should I use?
K factor is the position of the neutral axis as a fraction of the thickness, from 0 to 0.5, and real values sit below 0.5. Material, thickness and how tight the radius is all move it. 0.44 is a common starting value; a test bend on your material gives the exact number. Our K factor guide explains why.
Do I need to send ACP a flat pattern?
No. For a bent part, send a STEP of the formed shape. We make the flat from that geometry and form it on our TRUMPF press brakes, so the flat and the bends agree by construction. See sheet metal bending.
Have a bent part to make?
Upload the formed STEP for instant pricing and lead times. We make the flat, cut it and bend it in one shop.