Conical Taper — The Ratio Callout for Conical Surfaces

The conical taper symbol before a ratio states the rate of diameter change along a cone — (D − d)/L — replacing two end diameters with a single controlled value.

Definition

Conical taper is the ratio of the difference in the diameters of two sections perpendicular to the axis of a cone to the distance between those sections — taper = (D − d)/L. The symbol precedes that ratio as the dimension, e.g. 0.125 written after the taper glyph. One value controls the whole conical surface: the slope the tool must hold, stated independently of how long the cone is.

Standard tapers: name the series

Standard machine tapers — the American Standard Self-Holding and Steep Taper series — are usually dimensioned by specifying the taper name and number (a Morse or B5.10 designation) rather than computing a ratio. The diameter at the gage line and the length may also be specified; the taper in inches per foot and the small-end diameter may be shown as reference. The symbol-and-ratio callout is for tapers that are not a named standard series.

The four ways Y14.5 permits

• A basic taper and a basic diameter — the geometric method; a profile of a surface tolerance then controls the surface
• A size tolerance combined with a profile of a surface tolerance applied to the taper
• A toleranced diameter at both ends plus a toleranced length — applicable for noncritical tapers, such as the transition between diameters of a shaft
• A composite profile tolerance

Reading and drawing the symbol

The symbol is a right triangle — closed for taper, open for slope — and the standard requires it be shown with the vertical leg to the left, regardless of which way the actual cone runs on the drawing. The orientation is fixed so the symbol reads as a symbol, not as a sketch of the part. Taper on the drawing may run either direction; the symbol never changes.