Things You'll Need
White correction pen
Variable speed angle grinder
Diamond core hole saw bit
Onyx is a rare material used for high-end countertops. The soft stone requires the use of a diamond core bit. Drilling a hole through onyx requires careful planning and the right equipment. Common masonry bits are no match for the stone material, and using one risks damaging its surface. Applications that require drilling holes in onyx are usually associated with kitchen and bathroom countertop installation. Modern under-mount sinks require that the faucet be installed through the countertop versus traditional methods where the faucet is attached to the sink. Some applications require drilling several holes through the material to accommodate additional sprayers and soap dispensers.
Mark the location of the hole and its diameter on the onyx using a white correction pen in the applicable size. Holes for faucet applications are typically 1 1/4-inches in diameter.
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Install the diamond core hole saw bit onto the drill or variable speed angle grinder. Professional installers use the angle grinder because of its adjustable speed, which makes the tool superior to a standard drill when starting the hole.
Grip the angle grinder firmly while running at half speed and carefully lower the diamond core bit onto the hole location. Maintain a firm grasp on the tool to avoid it taking off and marring the surface of the onyx. Increase the speed to about 75 percent if necessary and continue cutting the hole until you break through the onyx.
Remove the bit from the hole, being careful that the onyx plug inside the bit does not fall out and damage countertop surface, sinks or flooring.
Slightly move the angle grinder a circular motion during drilling to wallow out the hole. This prevents the onyx core from becoming lodged in the diamond core bit.
The diamond core bit gets extremely hot; avoid touching it or placing it on a surface to prevent damage. Onyx is an expensive material; without moderate skills, working with the material is best left to professionals.