△ Taper / draft
Taper / draft · Indicadores dimensionales · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “1:20 draft or Morse taper” states a taper / draft requirement.
What controls
Callout for the inclination of one surface relative to another or to an axis, expressed as a ratio of the change in size to the length, or as an angle. The ratio and the angle describe the same thing but are not read the same way: a ratio always refers to a given length, and you must note whether it applies to the full diameter or to one side only, because the result differs by a factor of two. It is used both for functional tapers and for draft angles on molded or cast parts.
How to verify
On functional tapers, the practical method is to measure two diameters a known distance apart and calculate the inclination, or to use gauge balls or precision rollers on the taper to determine the angle accurately. To check actual contact on a mating taper, blue it against the mating part, which shows where it really bears. CMM measurement fits a cone and returns angle and position, which is the most complete method.
Common mistakes when interpreting it
- Applying a per-side taper ratio as if it were on the diameter, or vice versa.
- Checking the angle without verifying actual contact of the fit against the mating part.
- Measuring the draft angle relative to a part axis instead of the direction of pull.
How to get it in the workshop / if it comes out of tolerance
Before programming, clarify whether the ratio is on the diameter or per side, and over what length it is measured: this is the most expensive misinterpretation with tapers. On mating tapers, what matters is not just the angle but the resulting axial position, because a small angular error shifts the seating a long way. And with draft angles, remember they are measured relative to the direction of pull.
Contact at only one end of the taper when blued: the angle does not match the mating part; correct it before going any further, because cutting deeper will not fix it. Correct taper but seating displaced axially: the error is in the starting diameter, not the angle. And if the taper comes out barrel-shaped or concave, check rigidity, wear and finishing strategy.
Alternative symbol:1:10
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Other symbols in Dimension indicators
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