The complete body of this
Authenticator™ is machined from a solid 4 inch (101.6
mm) diameter piece of high-tensile stainless steel which is
heat treated to develop its maximum physical properties.
The one inch (25.4 mm) diameter Ultra Precise
Test Sphere is produced from very fine grained high chrome,
high carbon stainless steel. It is hardened to 58 Rockwell C
for wear- resistance and ultra-cold cycled for long term
dimensional stability.
The Ultra Precise Test Sphere is just that,
it is spherical within 2.5 micro inches (63.5 n m) maximum
and has a surface finish that is better than 0.5 micro inches
(12.7 n m) Ra. This is ten times more accurate than high
quality bearing balls. Spheres of this quality are generally not
commercially available.
Unlike tungsten carbide, this material has
good uniform electrical conductivity which is so important
for spindle bearing evaluation with capacitance gages.
The exact position of the Ultra Precise Test
Sphere is adjusted by a four screw wobble plate. The flexure
of this wobble plate is affected through an
integrally-machined ligature that achieves a careful balance
between flexibility and rigidity. The advantage of the four
screw adjustable wobble plate over a three screw wobble plate
is simplicity. There are no vector displacements to try and
interpret, simply loosen the screw corresponding to the most
positive displacement of the sphere and tighten the opposing
screw. When approaching the final setting, the tension on the
screw corresponding to the low point of the sphere is simply
increased and an entirely elastic bending achieves the final
movement of the sphere.
There are eight precisely-drilled holes
oriented around the outer edge of the flange of this device
that allow it to be securely clamped to the face of a spindle
using four or more socket head cap screws.
The same eight holes allow this device to be
rigidly attached to an extension shaft or magnetic adapter.
In this way, one device can be used in a multitude of
applications. There is a concentric counter-bore in the back
of the flanged Authenticator™. This counter bore
locates the shaft adapters concentric to the axis of the
ultra-precise sphere.
Each Authenticator™ has an individual
identification number permanently marked on its body.
An individual polar chart recording
documenting the roundness of the Ultra Precise Test Sphere is
supplied with each Authenticator™.
The Ultra Precise Test Sphere is attached to
the body of the Authenticator™ in a manner that
provides an ultra low electrical resistance between it and
the body. This is extremely important when using capacitance
gages for the critical evaluation of the spindle
characteristics.
The Ultra Precise Test Sphere is not just
glued to the body. A steel pin extends deep into a hole in
the sphere and into the body to achieve an extremely strong
connection. In order to preserve the dynamic balance of the
device, all details are maintained very symmetrical and
dimensionally balanced and constant. Each one of the four
socket head cap screws used to adjust the wobble plate are
carefully machined to give them exactly the same
mass.
