BIZOMAT MAKEOS · Power Transmission
Keyseat Depth and Measurement over Key
What depths should be measured when cutting this keyseat in a round shaft?
Chordal height at the keyseat edge, keyseat depth at the shaft centre-line, the measurement from the bottom of the keyseat to the opposite side of the shaft, and from the top of the key to the opposite side.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Shaft diameter | mm or in | Shaft diameter at the keyseat. |
| Key width | mm or in | Width of the key (and keyseat). |
| Keyseat depth at the side (from the edge) | mm or in | Depth of the keyseat measured at its side wall (from the key standard, e.g. t₁ in ISO or half the key height for square keys). |
| Key height | mm or in | Height of the key. |
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: Shaft diameter
- What it is
- The diameter of the shaft where the keyseat is cut, measured before cutting.
- Units and format
- Enter a number in mm or in: millimetres or inches, as long as every length uses the same unit. The form accepts 0.000001 mm or in to 100000 mm or in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 mm or in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the same unit for every input; the tool works in mm or inches alike.
What this means: Key width
- What it is
- The width of the key and of the keyseat slot cut for it, across the shaft.
- Units and format
- Enter a number in mm or in: millimetres or inches, as long as every length uses the same unit. The form accepts 0.000001 mm or in to 10000 mm or in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 mm or in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A wider key raises the chordal height Y, so the measurement S falls.
- Get it right
- It must be smaller than the shaft diameter; take it from the key standard for the shaft size.
What this means: Keyseat depth at the side (from the edge)
- What it is
- How deep the keyseat goes measured at its side wall, from where the wall meets the shaft surface down to the flat floor.
- Units and format
- Enter a number in mm or in: millimetres or inches, as long as every length uses the same unit. The form accepts 0.000001 mm or in to 10000 mm or in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 mm or in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- S falls one for one as the depth increases.
- Get it right
- This is depth at the side, not at the centre line; the key standard gives it (t₁ in ISO).
What this means: Key height
- What it is
- The overall height of the key, from its bottom face sitting on the keyseat floor to its top face.
- Units and format
- Enter a number in mm or in: millimetres or inches, as long as every length uses the same unit. The form accepts 0.000001 mm or in to 10000 mm or in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 mm or in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The measurement over the key rises one for one with key height; S does not change.
- Get it right
- Use the actual key, which can differ from the nominal height in the standard.
Method and formulas
- Chordal height Y = (D − √(D² − w²)) ÷ 2.
- Depth at centre-line = Y + t.
- S = D − Y − t (micrometer over the shaft from the keyseat floor); T = S + h (over the fitted key).
- Example: a 12 mm keyseat 5 mm deep in a 40 mm shaft measures 34.079 mm from its floor across the shaft.
Limitations
- Flat-bottomed keyseat; Woodruff keyseats are circular and have their own tables.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set the cutter depth when milling a keyseat
- Inspect keyseat depth with a micrometer over the shaft
- Check the key projection
Who it is for
- Machinists
- Quality inspectors
- Maintenance fitters
What you get
- Chordal height
- Depth at the centre-line
- Bottom of keyseat to opposite side of shaft
- Top of key to opposite side of shaft
Interpreting the result
- Measure S with a micrometer across the shaft to the keyseat floor.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2460–2486. Topic reference; no source tables or recommended settings are reproduced.
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