BIZOMAT MAKEOS · Quality
Dovetail Measurement over Rods
What should the measurement over (or between) rods read for this dovetail?
Measurement over rods for a male dovetail or between rods for a female dovetail slide, with a check that the rods touch the flanks below the edge.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Dovetail type | choice | Male for the tongue, female for the slot. |
| Dovetail angle (flank to base) | ° | Angle between flank and base from the drawing; 60° and 55° are common. |
| Width at the base corners | mm | Male: width across the base corners (narrowest). Female: width across the bottom corners of the slot (widest). |
| Rod diameter | mm | Measured diameter of the gauge rods or pins used. |
| Dovetail depth | mm | Height of the flank from the base to the edge. |
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: Dovetail type
- What it is
- Whether you are measuring the male dovetail (the tongue, measured over two rods) or the female dovetail (the slot, measured between two rods).
- Units and format
- Choose one of 2 options from the list: Male (tongue) – measure over rods; Female (slot) – measure between rods.
- Example
- The form opens with “Male (tongue) – measure over rods” selected as a worked example. Choose the option that matches your case.
- Get it right
- The width input means a different edge for each type, so set this first.
What this means: Dovetail angle (flank to base)
- What it is
- The angle between the sloping flank of the dovetail and its base, as given on the drawing.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 1° to 89.999°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the flank-to-base angle, not the angle from vertical or the included angle between two flanks.
What this means: Width at the base corners
- What it is
- The theoretical sharp-corner width at the base: for a male dovetail across the corners where the flanks meet the base (narrowest), for a female slot across its bottom corners (widest).
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The reading over or between rods changes by the same amount as this width.
- Get it right
- Use the sharp-corner drawing dimension; corner reliefs or radii do not change it.
What this means: Rod diameter
- What it is
- The actual diameter of the gauge rods or pins placed in the dovetail corners, both the same size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure the rods themselves; a small rod size error is multiplied in the reading.
What this means: Dovetail depth
- What it is
- The height of the dovetail flank, from the base up to the top edge. The tool uses it to check that the rods touch the flanks below the edge and to give the width at the top.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 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.
- Get it right
- If the rod contact point is above this depth, choose smaller rods.
Method and formulas
- Male: x = a + D(1 + cot(α ÷ 2)). Female: y = b − D(1 + cot(α ÷ 2)), where α is the dovetail angle and D the rod diameter.
- Contact height on the flank = (D ÷ 2) cot(α ÷ 2) sin α; it must be below the dovetail depth.
- Top width = base width ± 2h cot α.
- Example: a 60° male dovetail 50 mm at the base with 10 mm rods measures 77.321 mm over the rods.
Limitations
- Sharp corners are assumed; corner relief or radii do not change the reading provided the rods do not touch them.
- Rod diameter errors enter the reading multiplied by (1 + cot(α ÷ 2)).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Machine and inspect dovetail slides and gibs
- Write an inspection dimension for a drawing
- Choose a suitable rod size
Who it is for
- Quality inspectors
- Toolmakers
- Metrology technicians
What you get
- Measurement over or between rods
- Width at the top edge
- Rod contact height on the flank
Interpreting the result
- Choose a rod so that its contact point is clearly below the edge and clear of any corner relief.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 682. Topic reference; no source tables or recommended settings are reproduced.
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