Andy, looks like a DT, or double taper collet.
See this
Angles mean little in specs for tapers, for two reasons.
Remember these are mostly age old specifications and they didn't have CMM machines 100 years ago
Most angle measuring instruments or tools are too broad or are NOT sensitive enough to measure precise matching tapers.
Its like using a ruler to measure .001" dimensions
For example: Tapered bores are easily measured with standard instruments for the past 150 years, and using several different methods can confirm the actual taper.
Physical tapers are measured to the fourth decimal place.
The tangent of 1 degree is .017" per inch , so you would need to read to 1/170 th of a degree to match that level of precision.
If you had a Angle vernier dial, you could only do 1/17th of a degree, or 10 times less accurate.
To get an idea on this, note that some tapers are expressed in inches per foot, like .125" per foot- far superior to angular dimensions.
Also realize that today, we talk about decimal degrees....not used until recently with the digital revolution.
In the old days, it was degrees, hours, and minutes........ Can you imagine reading the taper at 3 degrees,27 min,21 seconds- Much easier to say .0604" per inch
Rich
See this
Angles mean little in specs for tapers, for two reasons.
Remember these are mostly age old specifications and they didn't have CMM machines 100 years ago
Most angle measuring instruments or tools are too broad or are NOT sensitive enough to measure precise matching tapers.
Its like using a ruler to measure .001" dimensions
For example: Tapered bores are easily measured with standard instruments for the past 150 years, and using several different methods can confirm the actual taper.
Physical tapers are measured to the fourth decimal place.
The tangent of 1 degree is .017" per inch , so you would need to read to 1/170 th of a degree to match that level of precision.
If you had a Angle vernier dial, you could only do 1/17th of a degree, or 10 times less accurate.
To get an idea on this, note that some tapers are expressed in inches per foot, like .125" per foot- far superior to angular dimensions.
Also realize that today, we talk about decimal degrees....not used until recently with the digital revolution.
In the old days, it was degrees, hours, and minutes........ Can you imagine reading the taper at 3 degrees,27 min,21 seconds- Much easier to say .0604" per inch
Rich
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