Back to the Basics:
Contact Points: Truncated or Not?
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Gagemaker uses contact point (or contact ball) gages to inspect lead, taper, height, and
pitch diameter on nearly any type of thread. Generally, these gages require two contact
points. Our points are interchangeable, one set of points often can be used on different
types of inspection gages. For best results, we still recommend one set of points for each gage.
Our contact points are carbide spheres precision ground to tolerances of +0.0002". This method produces a more accurate radius than the traditional grinding down of a barrel to create a ball.
While we do offer straight shank contact points, threaded shank points are our most common, as all of our contact point gages use threaded points. Threaded shanks are broken into spherical and truncated points.
While most of our points are spherical*, truncated points are used to measure pitch diameters of certain straight threads, primarily Acme, Stub Acme, and the modified Stub Acme threads.
Truncated points ensure contact on the flanks at the pitchline, just as if using a mic-over-wire method. Non-truncated points would bottom out on the thread's root (no longer touching the flanks at the pitchline).
*UN Series, Metric, 7x45 Buttress, and nearly all tapered threads (tubing & casing and rotary shouldered connections) use spherical points in measuring most thread elements.
Note: Remember when setting a gage with truncated points to set on the truncated surface of the point. Our set-to-flat values compensate for the truncation.
Look for more Gagemaker's Back to the Basics in the months ahead!