KEVOS® MAKEOS · Geometry
Bolt Circle Layout (Coordinates, Ligament, Edge and Wrench Clearance)
Where do the holes of this bolt circle go, is there enough metal between holes and to the edges, and will a socket fit between the bolts?
Layout of equally spaced holes on a bolt circle: angular step, adjacent centre chord and the coordinates of each hole (as the bolt circle tool), the ligament between neighbouring holes, edge distances to the outside and bore of the flange, whether the socket or wrench fits between neighbouring bolts, and the most bolts the wrench clearance allows on this circle.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bolt circle diameter | mm | Diameter of the circle through the hole centres. |
| Number of holes | Number of equally spaced holes. | |
| Angle of the first hole | ° | Angle of the first hole from the X axis, anticlockwise. |
| Hole diameter | mm | Diameter of the holes. |
| Flange outside diameter | mm | Outside diameter of the flange. |
| Flange bore (0 = solid) | mm | Diameter of the central bore (0 for a solid cover). |
| Socket or wrench clearance diameter | mm | Outside diameter of the socket or the swing clearance the wrench needs at each bolt. |
| Least ligament between holes | mm | Least metal you accept between neighbouring holes. |
| Least edge distance (hole edge to flange edge) | mm | Least metal you accept from a hole to the outside or bore edge. |
Method and formulas
- Step = 360° ÷ n; chord = BCD sin(180° ÷ n); hole i at (BCD ÷ 2) (cos θ_i, sin θ_i) (as the bolt circle tool).
- Ligament = chord − hole diameter; outside edge = (OD − BCD) ÷ 2 − d_h ÷ 2; bore edge = (BCD − ID) ÷ 2 − d_h ÷ 2.
- Socket fits if chord ≥ socket diameter; most bolts = ⌊180° ÷ sin⁻¹(socket ÷ BCD)⌋.
- Example: 4 holes on 100 mm are 70.711 mm apart with 59.711 mm ligament; up to 12 bolts leave room for the socket.
Limitations
- Equally spaced holes; unequal patterns need individual angles.
- Coordinates from the bolt circle centre; add the part datum offsets.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Lay out a flange or cover bolt pattern
- Check a design for wrench access
- Program hole positions for drilling
Who it is for
- Design engineers
- CNC programmers
- Drafters
What you get
- Angular step, chord and coordinates
- Ligament and edge distances
- Wrench fit and the most bolts it allows
Interpreting the result
- Wrench clearance, not ligament, usually limits the number of bolts on small circles.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 686. Topic reference; no source tables or recommended settings are reproduced.
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Open the Bolt Circle Layout (Coordinates, Ligament, Edge and Wrench Clearance) calculator
