BIZOMAT MAKEOS · Fabrication
Guillotine Shearing Force
What force does it take to shear this sheet or plate, and can the shear do it?
Shearing force for straight parallel blades or inclined (raked) blades, including the machine allowance, compared with the shear’s rated capacity.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Blades | choice | Parallel blades (croppers, punch-shears) or inclined blades (guillotines). |
| Material thickness | mm | Sheet or plate thickness. |
| Cut length (parallel blades) | mm | Length of the cut for parallel blades. |
| Tensile strength | MPa | Ultimate tensile strength of the material from its certificate. |
| Shear strength ÷ tensile strength | Shear strength as a fraction of tensile strength (about 0.7–0.8 for steels). | |
| Blade rake angle | ° | Rake angle of the upper blade (inclined blades). |
| Relative blade penetration at fracture | Fraction of the thickness the blade penetrates before fracture, from the material table (softer materials penetrate more). | |
| Inclined blade factor n | Factor for inclined blades, about 0.75–0.85 for most materials. | |
| Shear rated capacity | kN | Rated force of the shear from its plate or manual. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Blades
- What it is
- Whether the cut is made with straight blades parallel to each other along the whole cut, as in croppers, or with an inclined upper blade that cuts progressively, as in a guillotine.
- Units and format
- Choose one of 2 options from the list: Straight parallel blades; Straight inclined (raked) blades.
- Example
- The form opens with “Straight inclined (raked) blades” selected as a worked example. Choose the option that matches your case.
- Get it right
- Parallel blades use cut length; inclined blades use rake, penetration and the blade factor instead.
What this means: Material thickness
- What it is
- The thickness of the sheet or plate being cut.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Force rises in proportion for parallel blades and with the square of thickness for inclined blades.
- Get it right
- Measure the actual thickness; plate is often thicker than its nominal size.
What this means: Cut length (parallel blades)
- What it is
- The length of material cut in one stroke with parallel blades. Not used for inclined blades.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Force rises in direct proportion.
- Get it right
- Used only for parallel blades; for a guillotine the rake sets how much is cut at once.
What this means: Tensile strength
- What it is
- The ultimate tensile strength of the material being cut, from its mill certificate or material specification.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 3000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 450 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Shearing force rises in direct proportion.
- Get it right
- Use the actual certificate value where possible; it is often above the minimum specified.
What this means: Shear strength ÷ tensile strength
- What it is
- The shear strength of the material divided by its tensile strength, used to turn tensile strength into the shear strength the blades must overcome.
- Units and format
- Enter a plain number with no unit. The form accepts 0.3 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Shearing force rises in direct proportion.
- Get it right
- Enter a fraction, not a percentage. Take it from material data for your alloy.
What this means: Blade rake angle
- What it is
- The angle between the inclined upper blade and the lower blade, from the shear’s manual or setting. Used only for inclined blades.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0.1° to 30°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger rake lowers the force but can twist or bow narrow strips.
- Get it right
- Used only for inclined blades. Enter degrees.
What this means: Relative blade penetration at fracture
- What it is
- How far the blade enters the material, as a fraction of thickness, before the remaining section breaks. Softer, more ductile materials penetrate further. Used only for inclined blades.
- Units and format
- Enter a plain number with no unit. The form accepts 0.05 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Force for inclined blades rises in direct proportion.
- Get it right
- Enter a fraction of thickness, not millimetres or a percentage; take it from shearing data for the material.
What this means: Inclined blade factor n
- What it is
- A correction factor in the inclined-blade force formula that allows for how the material behaves under a raked blade, from shearing data. Used only for inclined blades.
- Units and format
- Enter a plain number with no unit. The form accepts 0.5 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Force for inclined blades rises in direct proportion.
- Get it right
- Used only for inclined blades; take it from the same source as the penetration value.
What this means: Shear rated capacity
- What it is
- The maximum cutting force the shear is rated for, from its nameplate or manual.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 1000000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only changes the utilisation and the pass or fail line.
- Get it right
- Also check the maker’s maximum thickness for this material strength, which can limit before force does.
Method and formulas
- Parallel blades: F = τ × b × t, with τ = ratio × UTS; machine force = 1.3F.
- Inclined blades: F = n × k × UTS × λ × t² ÷ tan φ, with k the shear ratio, λ the relative penetration and φ the rake angle.
- Example: 6 mm plate of 450 MPa with a 2° rake needs about 118.76 kN.
Limitations
- Blade clearance, dull blades and thickness variation raise the force; the 30% allowance covers typical cases only.
- Rated capacity on a shear is usually stated for mild steel of a given strength; scale for stronger materials.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether a shear can cut a plate
- Compare rake angles
- Estimate force for flat bar cropping
Who it is for
- Fabrication supervisors
- Manufacturing engineers
- Estimators
What you get
- Shearing force
- Machine force with allowance
- Utilisation of the shear capacity
Interpreting the result
- Use the machine’s stated maximum thickness for the material strength as well as the force check.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1336–1339. Topic reference; no source tables or recommended settings are reproduced.
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