- Use M=F×L to screen cantilever root moment.
- Bolt spacing and bearing faces strongly affect joint load.
- Holes, bends and reinforcement must support one load path.
- Dimension from functional datums and prototype-test the worst case.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
Define Load Cases First
Record load magnitude, direction, point of action, impact/vibration, cycle count and consequence of failure. A first-pass cantilever moment is M=F×L: a 100 N load located 200 mm from the mounting face creates 20 N·m static moment before impact and safety factors. For changing loads, check reverse, lateral and torsional cases.
Treat the Fastener Pattern as a Loaded Joint
A small bolt-pattern lever arm creates higher bolt tension for the same overturning moment. Increasing vertical spacing and adding a bearing face against the support can outperform a larger bolt. Check bolt tension/shear, hole bearing, edge tear-out, preload, slip and tool access. Where slots provide adjustment, align them with assembly variation and avoid uncontrolled slip along the primary load direction.
Protect Bend Roots and Hole Edges
Use an inside radius achievable with stable tooling. For mild steel, r≈1t is a practical DFM starting point; stainless and hard-temper aluminum generally need more, subject to material data and test bends. As a conservative initial screen, keep hole-center-to-material-edge distance around ≥1.5d unless calculated otherwise. Screen hole-edge-to-bend-tangent distance near r+2t, then confirm against the actual V-die and hole geometry.
Reinforce the Moment Path
A gusset should connect the loaded arm to the mounting face and reach the high-stress root. Beads and return flanges should cross the flexible zone. A gusset placed in a low-stress area adds cost without reducing root stress. Avoid abruptly terminating reinforcement at a peak-stress location, which can create a fatigue hot spot.
Dimension from Functional Datums
Use the mounting face as datum A, a locating edge as B and a third feature as C. Control the hole pattern from A|B|C rather than chaining from several cut edges. Specify formed angle, mounting-face flatness and post-finish hole/slot requirements. For welded brackets, separate pre-weld part dimensions from post-weld assembly CTQs.
VALIDATION CHECKLIST
- Static, impact, fatigue and misuse load cases
- Root stress, overall deflection and local buckling
- Bolt group, hole edge, weld and bearing face
- Tooling, bend sequence and fastening access
- Worst-direction prototype load test and permanent-set record