There are two schools of thought regarding how the Precision Calibration Sphere should be attached to the mounting tool.

The first method is to glue a complete Precision Calibration Sphere directly to the tool. Any sharp blow will send such a sphere bouncing across the room. Proponents of this method contend that if the sphere is struck such a hard blow, it would be permanently damaged and no longer suitable for use as a calibration device. They feel that, in effect, this method acts as a kind of safety fuse.

Besides the friability of the joint, this method has a couple of other characteristics. For a simple glue joint to have adequate holding power, a large diameter boss is required. This large boss reduces the available spherical surface for calibration use. As the glue cures, tensile stresses are created across the large diameter boss, which can cause considerable distortion of the Precision Calibration Sphere. Using this technique, the gluing procedure is extremely critical: the proportions of catalyst to resin, the cleanliness of the part surfaces - even high humidity in the room - are all important factors.

In the second method, a small diameter steel pin is inserted into a pre-drilled hole in the Precision Calibration Sphere and in the center of the conical cup at the time that the glue is applied. The steel pin raises the sheer strength of the assembly several orders of magnitude. This gives a much tougher assembly that will not fall apart during normal shipping and handling. Using this technique, the gluing procedure is much less critical. The dramatic increase in joint strength allows a much smaller diameter boss to be used, thus increasing the area of the spherical surface available for calibration.

"A" diameter is 1/2 the ball diameter "A" should be 1/4 to 1/3 the ball diameter. "B" should be slightly less than the hole depth. "C" should be the same as the hole depth in the ball.

The hole diameters and depths that we have chosen will not cause significant distortion of the sphere. They are, however, large enough and deep enough to give good holding power. Although we will custom-drill any size hole to any depth you specify, larger, deeper holes can cause considerable distortion of the Precision Calibration Sphere.

We recommend a high shear-strength glue, which cures at room temperature, to attach the ball to the boss of the tool. Using this material, the glue line should be 0.0025 to 0.004 inches (0.063mm-0.10mm) This is equivalent to a diametrical clearance of 0.005 - 0.008 inches (0.127 - 0.203mm) between the holes in the sphere and the boss and the steel pin.

A very high-shear glue for both of these application is supplied under catalog #EG-3000. This glue has a high percentage of filler material giving it a low rate of thermal expansion. Equal volumes of the resin and the catalyst are simply well mixed together and the glue is ready to apply. EG-3000 is a ceramic filled epoxy glue with a 3000 pound per square inch shear strength ( 3000 lb / in^2, 1025 kg/ cm^2 ).

A shallow conical cup should be machined in the tool. The conical surface and the Precision Calibration Sphere are first cleaned with mineral spirits (paint thinner) and then with acetone. These solvents can be purchased from a local hardware store. Be sure to follow safety instructions supplied with these materials. A small amount of the pre-mixed glue is applied to both surfaces. No air bubbles can be allowed in the joint. The surfaces are held together under pressure during curing. The proper steel pin is supplied with each of the UBB and PBB series balls having a pre-drilled hole, except the UBB-39, for which a 0.125 inch (3.18mm) diameter by 0.85 inch (21.59mm) long tungsten carbide pin is supplied.