Measuring female tapers

[mklotz]

A traditional method for measuring a female taper has been to use two gage balls of appropriate diameters. Insert the smaller into the taper and measure its depth below the taper mouth. Repeat with a larger ball. Knowing the ball diameters and the derived separation between their centers, calculating the taper is simple...

or use the FTAPER program from my site.

Most hobbyists probably won't have a set of ball gages; they're expensive and only infrequently used. Thankfully, there's a simpler, slightly less accurate way to make the measurement.

Machine the end of a suitably-sized rod (I prefer brass so as not to mar the taper walls) to a diameter (d2) that will fit into the taper near the mouth. Measure this diameter carefully with a micrometer and note the value. Insert the rod until it contacts the bore and measure how far it has penetrated (h2). Some means of holding the rod parallel to the bore of the taper will be needed while the depth measurement is made.

Now, turn down the d2 diameter a bit to a value (d1) and repeat the above to establish the depth h1.

The half angle of the taper is then given by...

taper half angle = arctan[ 0.5 * (d2 - d1) / |h2 - h1| ]

where the vertical bars, "|", denote absolute value.