BIZOMAT MAKEOS · Manufacturing
Countersink Depth and Breakthrough
How deep is this countersink, and will it reach the opposite face?
Resolve axial cone depth from pilot diameter, mouth diameter and included angle, then compare it with material thickness.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Pilot-hole diameter | mm | Finished cylindrical pilot-hole diameter. |
| Countersink mouth diameter | mm | Required diameter at the entry face; at least the pilot diameter. |
| Included cone angle | ° | Full included cone angle, verified from the tool and drawing. |
| Material thickness | mm | Axial thickness from the entry face to the opposite face. |
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: Pilot-hole diameter
- What it is
- The diameter of the straight through hole that the countersink cone starts from, as finished.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 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
- A larger pilot makes the cone shallower for the same mouth diameter.
- Get it right
- Use the finished hole size, not the drill point or a nominal clearance size you have not checked.
What this means: Countersink mouth diameter
- What it is
- The diameter of the countersink where it meets the entry face, the widest part of the cone, as required by the drawing or the screw head.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger mouth diameter makes the cone deeper.
- Get it right
- It must be at least the pilot diameter; measure at the surface, not where a chamfer edge looks finished.
What this means: Included cone angle
- What it is
- The full included angle of the countersink cone, measured across both sides of the cone, as marked on the countersink tool or drawing.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0.01° to 179.99°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller included angle makes the cone deeper for the same diameters.
- Get it right
- Use the included angle, not the half-angle from the axis; check it matches the screw head angle.
What this means: Material thickness
- What it is
- The thickness of the material from the entry face to the opposite face, along the hole axis.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the cone depth, only the remaining material and the breakthrough check.
- Get it right
- Measure the actual sheet or plate at the hole; nominal sheet thickness can differ.
Method and formulas
- h = (mouth − pilot)/[2 tan(included angle/2)]. Remaining thickness = thickness − h.
- Mouth diameter at just-through depth = pilot + 2 × thickness × tan(angle/2).
- Example: 6 mm pilot, 12 mm mouth and 90° included angle gives 3 mm depth, leaving 2 mm in 5 mm material.
Limitations
- Ideal coaxial cone and cylindrical pilot; burrs, runout and tolerances are excluded.
- Zero or negative remaining thickness is reported as breakthrough. Positive remaining material is not proof of adequate strength.
- This is geometry, not a fastener-seat standard or a counterbore calculator.
- Default values are worked examples, not recommended settings or material properties.
Typical uses
- countersink geometry
- remaining wall
- breakthrough
Who it is for
- Machinists
- Design engineers
What you get
- Axial depth
- Remaining axial thickness
- Mouth diameter at just-through depth
Interpreting the result
- Confirm the drawing uses the included angle.
- Verify a trial part and assess the minimum-thickness tolerance condition.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 852–853. Topic reference; implementation and examples are original, and no source tables are reproduced.
- Method: right-triangle geometry of the cone half-angle.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.