Accurately Calculate Bend Deduction with Our Calculator & Chart

Looking to master the art of sheet metal bending?

Look no further than the bend deduction method. This straightforward algorithm, also known as the “back-off amount,” is a must-know for any sheet metal fabricator.

But what exactly is bend deduction, and how does it work?

This comprehensive guide from MachineMfg has all the answers. From the neutral axis to the bend angle, bend radius, K-factor, and inside radius, this article breaks down all the factors that can affect your bend deduction.

Plus, it includes a handy formula for calculating the bending deduction coefficient in sheet metal fabrication, as well as a chart and table for reference.

Whether you’re a seasoned pro or just starting out in the world of sheet metal bending, this guide has everything you need to know to take your skills to the next level.

So why wait? Dive in and start mastering the art of sheet metal bending today!

What Is Bend Deduction?

Bend deduction is commonly referred to as the “back-off amount”. It is a straightforward algorithm used to explain the process of sheet metal bending.

The bend deduction method states that the flattened length (L) of a part is equal to the sum of the lengths of the two flat parts extending to the “cusp” (the point where the two flat parts intersect virtually) minus the bend deduction (BD).

Factors Affect Bend Deduction

There are several factors that affect Bend Deduction, including the Neutral Axis, Bend Angle, Bend Radius, K-Factor, and Inside Radius.

Neutral Axis

The Neutral Axis is an imaginary line that runs through the center of the material being bent. It is the line where the material experiences neither compression nor tension during bending. The position of the Neutral Axis depends on several factors, including the material properties and the bend radius.

Bend Angle

The Bend Angle is the angle formed by the two legs of the bend. It is important to note that this angle is measured on the inside of the bend. The Bend Angle affects the amount of material that must be removed in order to achieve the desired flat pattern.

Bend Radius

The Bend Radius is the radius of the arc formed by the bend. It is measured on the inside of the bend. The Bend Radius affects both the position of the Neutral Axis and the amount of material that must be removed in order to achieve the desired flat pattern.

K-Factor

The K-Factor is a property of the material being bent. It determines how much the material will stretch when it is bent. The K-Factor is used to calculate both the position of the Neutral Axis and the amount of material that must be removed in order to achieve the desired flat pattern.

Inside Radius

The Inside Radius is the radius of curvature on the inside surface of a bend. It is determined by both the Bend Radius and material thickness. The Inside Radius affects both the position of the Neutral Axis and how much material must be removed in order to achieve a desired flat pattern.

Bend Deduction Formula

How to calculate the bending deduction coefficient in sheet metal fabrication?

The bending deduction in sheet metal fabrication is a term used in the setting parameters of Solidworks and is also a formula used for many years in sheet metal fabrication workshops. Let’s take a look at the calculation formula in Solidworks.

Lt = A + B – BD

Where:

  • Lt is the total unfolded length
  • A and B are as shown in the figure
  • BD is the bending deduction value.

The bending deduction in Solidworks is only used for the calculation of 90-degree bends in sheet metal.

However, it can also be used for the calculation of non-90-degree sheet metal unfolding, but the bending deduction value for non-90-degree bending needs to be used according to the bending coefficient table.

Each manufacturer has a different table, and there may be errors. Some sheet metal factories may not use non-90-degree bending often.

Today, I will mainly share the calculation method of the bending deduction for 90-degree bending that I am familiar with.

Today, I will share the calculation method for the bending deduction of 90-degree bending that I am familiar with.

There are roughly three algorithms for calculating bending deductions:

  1. 1.7 times the thickness of the material.

Sheet metal factories generally use 1.7 times the thickness of the material as the bending deduction, which is the simplest calculation method for sheet metal unfolding.

However, it is not very accurate. If the precision requirement is not high in sheet metal processing, it can be directly used.

Different materials may also have different values; aluminum plates can be calculated based on 1.6 times the thickness of the material, while stainless steel plates can be calculated based on 1.8 times the thickness of the material.

  1. Bending deduction = 2 times the thickness of the material + 1/3 the thickness of the material.

This bending deduction calculation formula has been summarized by the sheet metal manufacturing industry for a long time and is also a rough calculation method.

The theoretical explanation of this calculation formula is: Sheet metal unfolding = Length A + Length B – 2 times the thickness of the material + 1/3 the thickness of the material’s elongation coefficient.

The calculation starts by adding up the lengths of the shortest straight line and the elongation factor. It is believed that the sheet metal will elongate during the bending process.

  1. Bending deduction = 2 times the thickness of the material – (0.72t-0.075V-0.01).

This formula is derived from a journal article online. Its feature is that it considers the influence of the width of the lower die on the bending deduction.

The test data is derived from experiments on carbon steel plates, and the accuracy of usage for other materials is unknown. I used this formula for the unfolded calculation of a one-time aluminum plate bent with a slot width of 4 times the thickness of the material, and the resulting numerical value was relatively accurate. This formula is very accurate for unfolded calculation of carbon steel plates.

Explanation: t is the actual thickness of the sheet metal, and nominal thickness should not be used for calculation. The above two methods have rough calculations and are not strict in thickness requirements. This formula needs to be calculated based on the actual thickness measured by calipers.

V is the width of the slot in the lower die during bending. Generally, 6-8 times the thickness of the material is taken as the slot width. The actual amount used is calculated according to the actual usage, for example: using 10 lower die bending for 1.5.

There are many methods for calculating bending deductions, including formulas based on the neutral layer theory. This formula is not conducive to actual sheet metal processing, so it is not mentioned here.

The above three methods are the most practical and simplest sheet metal bending deductions or unfolding calculation methods suitable for sheet metal factories.

Bend Deduction Calculator

Other related calculators:

Bend Deduction Chart

Sheet metal material bending deduction table

VDie width
w
Bend RadiusT30°45°60°90°120°150°180°90°double bend outer layerHMinimum size of Z-bend (Z)
8.012.0R10.60.20.50.91.00.70.20.31.96.010.0
0.80.30.61.01.60.80.30.42.2
10.30.71.11.70.90.30.52.5
1.20.40.81.32.21.10.40.62.8
R20.60.20.50.91.60.70.20.31.9
0.80.30.61.21.80.80.30.42.2
10.30.71.22.00.90.30.52.5
1.20.40.81.42.31.10.40.62.8
10.014.0R11.50.71.21.62.51.30.50.73.27.011.0
R21.50.61.01.52.71.30.50.73.5
12.016.0R120.61.32.03.41.70.60.94.48.513.0
R220.91.42.03.61.70.60.94.5
16.026.0R12.50.71.52.44.32.20.81.15.612.020.0
30.81.72.85.12.80.81.35.8
R22.50.81.62.54.82.30.91.16.2
31.02.03.05.22.81.01.36.4
22.032.5R141.02.43.56.53.31.1  16.026.0
R241.22.64.06.83.51.1  
32.050.0R151.23.24.88.64.61.4  24.038.0
61.53.54.59.55.01.8  
R251.53.45.08.84.51.6  
61.83.85.59.85.22.0  

Explanation:

  • T: Material thickness;
    V: Lower die groove width;
    W: Lower die width;
    α: Internal angle after bending;
    H: Minimum distance from the bending center of the die to the edge of the material;
    Z: Minimum size of Z-bend.
  • Unfold formula: L = A + B – K; (A, B: Outer dimensions of the part; K: Material bending coefficient);
  • Expanded size of flattened steel plate: L = A + B – 0.45T;
  • Expanded size of pressed steps: L = A + B – 0.3T;
  • Minimum size of Z-shaped bend: Z = W/2 + 2T + 1;
  • The deduction coefficients for cold-rolled steel plate, aluminum-zinc coated plate, stainless steel plate, electrolytic plate, and aluminum plate are the same;
  • According to the current upper die conditions of the company, the bending coefficient of upper die R1 is suitable for cold-rolled steel plate, aluminum-zinc coated plate, and stainless steel plate; The bending coefficient of upper die R2 is suitable for aluminum plate, copper plate, electrolytic plate, etc.

Mild Steel Bend Deduction Chart

Formula0.2t0.4t0.6t0.8t1.0t1.2t1.4t1.6t
Angle155°
~165°
145°
~155°
135°
~145°
125°
~135°
115°
~125°
105°
~115°
95°
~105°
85°
~95°
Thickness
(t)
15°~25°25°~35°35°~45°45°~55°55°~65°65°~75°75°~85°
0.5 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 
0.6 0.12 0.24 0.36 0.48 0.60 0.72 0.84 0.96 
0.8 0.16 0.32 0.48 0.64 0.80 0.96 1.12 1.28 
1.0 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 
1.2 0.24 0.48 0.72 0.96 1.20 1.44 1.68 1.92 
1.5 0.30 0.60 0.90 1.20 1.50 1.80 2.10 2.40 
2.0 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 
2.5 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 
3.0 0.60 1.20 1.80 2.40 3.00 3.60 4.20 4.80 
4.0 0.80 1.60 2.40 3.20 4.00 4.80 5.60 6.40 
4.5 0.90 1.80 2.70 3.60 4.50 5.40 6.30 7.20 
5.0 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 
6.0 1.20 2.40 3.60 4.80 6.00 7.20 8.40 9.60 

Stainless Steel Bend Deduction Chart

Formula0.3t0.5t0.7t0.9t1.1t1.3t1.5t1.7t
Angle155°
~165°
145°
~155°
135°
~145°
125°
~135°
115°
~125°
105°
~115°
95°
~105°
85°
~95°
Thickness (t)15°
~25°
25°
~35°
35°
~45°
45°
~55°
55°
~65°
65°
~75°
75°
~85°
0.5 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 
0.6 0.18 0.30 0.42 0.54 0.66 0.78 0.90 1.02 
0.8 0.24 0.40 0.56 0.72 0.88 1.04 1.20 1.36 
1.0 0.30 0.50 0.70 0.90 1.10 1.30 1.50 1.70 
1.2 0.36 0.60 0.84 1.08 1.32 1.56 1.80 2.04 
1.5 0.45 0.75 1.05 1.35 1.65 1.95 2.25 2.55 
2.0 0.60 1.00 1.40 1.80 2.20 2.60 3.00 3.40 
2.5 0.75 1.25 1.75 2.25 2.75 3.25 3.75 4.25 
3.0 0.90 1.50 2.10 2.70 3.30 3.90 4.50 5.10 
4.0 1.20 2.00 2.80 3.60 4.40 5.20 6.00 6.80 
4.5 1.35 2.25 3.15 4.05 4.95 5.85 6.75 7.65 
5.0 1.50 2.50 3.50 4.50 5.50 6.50 7.50 8.50 
6.0 1.80 3.00 4.20 5.40 6.60 7.80 9.00 10.20 

Bend Deduction Chart for Cold Rolled Steel Plates at Various Angles

  1. The following table shows the deduction factor for each 5-degree angle increment from 90 degrees outward: (180°-n°)÷90°×(deduction factor at 90°).
  2. The inside bending radius is uniformly set to R0.2, and the gap distance is set to G0.2.
No.Angle
/Thickness
0.8 1.01.21.52.02.53.04.05.0
103.003.604.005.007.008.4010.0014.0020.00
252.923.503.894.866.818.179.7213.6119.44
3102.833.403.784.726.617.939.4413.2218.89
4152.753.303.674.586.427.709.1712.8318.33
5202.673.203.564.446.227.478.8912.4417.78
6252.583.103.444.316.037.238.6112.0617.22
7302.503.003.334.175.837.008.3311.6716.67
8352.422.903.224.035.646.778.0611.2816.11
9402.332.803.113.895.446.537.7810.8915.56
10452.252.703.003.755.256.307.5010.5015.00
11502.172.602.893.615.066.077.2210.1114.44
12552.082.502.783.474.865.836.949.7213.89
13602.002.402.673.334.675.606.679.3313.33
14651.922.302.563.194.475.376.398.9412.78
15701.832.202.443.064.285.136.118.5612.22
16751.752.102.332.924.084.905.838.1711.67
17801.672.002.222.783.894.675.567.7811.11
18851.581.902.112.643.694.435.287.3910.56
19901.501.802.002.503.504.205.007.0010.00
20951.421.701.892.363.313.974.726.619.44
211001.331.601.782.223.113.734.446.228.89
221051.251.501.672.082.923.504.175.838.33
231101.171.401.561.942.723.273.895.447.78
241151.081.301.441.812.533.033.615.067.22
251201.001.201.331.672.332.803.334.676.67
261250.921.101.221.532.142.573.064.286.11
271300.831.001.111.391.942.332.783.895.56
281350.750.901.001.251.752.102.503.505.00
291400.670.800.891.111.561.872.223.114.44
301450.580.700.780.971.361.631.942.723.89
311500.500.600.670.831.171.401.672.333.33
321550.420.500.560.690.971.171.391.942.78
331600.330.400.440.560.780.931.111.562.22
341650.250.300.330.420.580.700.831.171.67
351700.170.200.220.280.390.470.560.781.11
361750.080.100.110.140.190.230.280.390.56
371800.000.000.000.000.000.000.000.000.00

Determining Flange Lengths and Total Length

You can use our sheet metal bending calculator for free to quickly calculate important parameters in sheet metal bending, including the K-factor, Y-factor, bend allowance, bend deduction, arc length, and unfolding flat size.

FAQs

1. What is Bend Deduction? 

Bend Deduction is a value used to explain the process of sheet metal bending. It is defined as the material you will have to remove from the total length of your flanges in order to arrive at the flat pattern. The flange lengths are always measured to the apex of the bend.

2. How is Bend Deduction Calculated? 

Bend Deduction is calculated using a formula that takes into account several factors, including material thickness, bend angle, inside radius, and k-factor. The formula for Bend Deduction incorporates both the Outside Setback and Bend Allowance.

3. What is the difference between Bend Allowance and Bend Deduction? 

Bend Allowance is an approximation of the bend’s total length. It is measured along the neutral axis of the material. By definition, the bend deduction is the difference between the bend allowance and twice the outside setback.

4. What is a Bend Deduction Calculator? 

A Bend Deduction Calculator is a tool that helps you calculate the correct values for your sheet metal bending projects, ensuring accurate results and minimal waste.

5. How does a Bend Deduction Calculator work? 

A Bend Deduction Calculator calculates bend allowance/deduction based on material thickness, bend angle, inside radius, and k-factor. You input your parameters and the calculator processes these variables through the equations to determine the Bend Deduction.

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About The Author

4 thoughts on “Accurately Calculate Bend Deduction with Our Calculator & Chart”

  1. Hello,

    I have been struggling to find the bending duction formula
    Is it possible to supply the bending duction formula given above?

  2. Satish Walimbe

    Is your “BEND DEDUCTION CALCULATOR” valid for M.S. Cold Rolled Sheet, and S.S.-304 Sheet too?

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