KEVOS® MAKEOS · Strength
C-Frame Throat Check (Curved-Beam Stress, Straight-Beam Comparison, Depth Needed)
Is the throat of this C-frame press or clamp strong enough, how much does the inside corner curvature raise the stress, and what throat depth would meet my allowable?
Check of the throat section of an open-gap C-frame (press frame, punch frame, clamp or hook-shaped bracket) under the working force: direct tension plus bending from the force acting at the gap depth, with the curved-beam stresses at the inner and outer fibres from the neutral-axis shift (as the curved beam tool), the straight-beam combined stress for comparison (as the combined axial and bending stress tool), the curvature factor, and the throat depth needed to bring the inner fibre to your allowable.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Working force across the gap | kN | Force the frame resists across its gap (press tonnage, clamp force). |
| Gap depth (load line to inner face of throat) | mm | Horizontal distance from the line of the force to the inner face of the throat. |
| Throat depth (inner to outer face) | mm | Depth of the rectangular throat section from inner to outer face. |
| Throat width (total plate thickness) | mm | Width of the throat section (total thickness of the side plates for a plate frame). |
| Inner radius of the throat corner | mm | Radius of the inside corner of the throat, measured to the inner face. |
| Allowable stress | MPa | Allowable tensile stress for the frame material and duty. |
Method and formulas
- Moment = P × (a + h ÷ 2) about the section centroid.
- Curved beam: r_n = h ÷ ln(r_o ÷ r_i), e = r_c − r_n; σ_i = P ÷ A + M (r_n − r_i) ÷ (A e r_i); σ_o = P ÷ A − M (r_o − r_n) ÷ (A e r_o) (as the curved beam tool).
- Straight beam σ = P ÷ A + 6M ÷ b h² (as the combined axial and bending stress tool); depth needed found by solving σ_i = allowable.
- Example: the inner corner carries 99.063 MPa against 60 MPa by straight-beam theory (×1.651); a 258.48 mm throat meets 120 MPa.
Limitations
- Rectangular throat; I or T sections need their own neutral-axis shift.
- Static stress; press frames also need a fatigue and gap-deflection check.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a C-frame press or punch frame
- Size the throat of a clamp or bracket
- Show why the inside corner of a frame cracks first
Who it is for
- Machine designers
- Press tool designers
- Design engineers
What you get
- Curved-beam inner and outer fibre stresses
- Straight-beam stress and curvature factor
- Throat depth needed
Interpreting the result
- The tighter the corner radius, the more the inner fibre stress exceeds the straight-beam value.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 212–218, 257–260. Topic reference; no source tables or recommended settings are reproduced.
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