|Established in 1952
Tuesday, June 18, 2013
Producing one of a kind or small quantities of spherical gage tips by conventional machining is a difficult and expensive proposition. Setting up a machine to produce a high quality tiny thread against a shoulder is challenging.
It is desirable to have the thread made of a hard stiff material, but machining such a material straight, concentric, and with a good thread forms in a tiny #4-40 or #2-56 thread is an expensive proposition. The solution is simple, and it's inexpensive. By drilling a small concentric hole in a hard steel or tungsten carbide ball by Electrical Discharge Machining ( EDM) and gluing in a length of high quality rolled threaded stock, the problem is solved.
To further enhance the design, a precision nut is added on the top of the ball. If required, a cylindrical spacer can be inserted between the top of the ball and the nut. The design is quite rugged, as the epoxy glue used in the assembly is a ceramic filled material, with a shear strength of 3000 pounds per square inch.
In addition, the axial load developed by screwing the tip onto the gage is applied between the nut and the thread, but not in the glue joint between the ball and the thread.
The measuring force is 100% compressive stress, so there is no tendency to pull the assembly apart in every day use.
The average cost of a ball gage tip is $36.00.
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