A: To drill a hole that wide and deep through stone — especially a particularly hard type such as quartz — is a job for a core-drilling bit impregnated with diamond abrasive and a drill that feeds water down through the bit to keep the tip cool and rinse away debris. You might be able to find a countertop manufacturer who will cut the hole for you, because these fabricators use diamond core bits to cut holes for pipes to faucets. However, the bits they typically use are just a few inches long, enough to go through countertops.
Companies that specialize in concrete drilling and sawing are a better fit for a job like yours. They typically drill through basement walls, concrete floors and ceilings, and other concrete and stone surfaces to create pathways for pipes and anchor holes for railings. Diamond Core Drilling and Sawing in Riverdale Park, Md. (301-277-5100; diamondcore.com) takes on small jobs like yours. Manager Bob Haithcock said that if you brought the rock to the company’s shop, the cost would be just the shop fee, billed at $75 an hour. It should take less than an hour, but you would probably need to make separate trips for delivery and pickup. This is the kind of service the company fits in when the shop isn’t busy with bigger jobs, Haithcock said.
For a single hole in one rock, going to a company such as Diamond Core makes the most sense. But if you need holes in multiple rocks or if the rock you want to use is too big to transport, you could explore other options, including renting a drill and a bit and doing the work yourself, assuming you’re relatively handy and strong. Many Home Depot stores (including those in Washington and Hyattsville, Md., but not Alexandria, Va.) rent a Hilti core drill rig that can be used either in a stand, like a drill press or as a handheld tool, which is how you’d probably use it for a job like yours. The price is $79 for up to four hours, or $113 a day, plus bit rental at $9 a day. The drill weighs about 18 pounds. You would also need work gloves, boots, and eye and ear protection.
If you were drilling only a shallow hole, there are ways to rig up a water-cooling system for a diamond bit without having to get a drill that feeds water into the bit. For example, you could press plumber’s putty into a ring around the area and fill that with water to create a puddle around the bit. But because you want to drill eight inches deep, this won’t work. The tip would be dry.
Hammer drills and rotary hammers (also known as rotary hammer drills) can also drill through some types of rock, and they’re great for making holes in concrete. Both types provide a hammering action that helps the bit work. But quartz is much harder than many rocks, and it often has a structure that consists of “a bunch of crystals pushed together,” said Ethan Currier, an artist who often drills into stone to create garden artwork (203-364-7146; ethancurrierart.com). “You’d risk blowing it up” if you tried to drill through quartz with a tool that delivers a hammering action, he said.
Or, taking an entirely different approach, you could decide to forgo trying to drill into stone and instead create a stonelike anchor made of concrete. Mold the concrete around a piece of PVC plastic pipe that will become a sleeve your birdhouse-supporting pipe can slip through. PVC piping is rated by its inside diameter, but test first to decide whether your pipe will slip easily through three-quarter-inch PVC, or whether one-inch diameter pipe would work better. A two-foot-long piece of three-quarter-inch PVC pipe is $1.60 at Home Depot. Tape over the ends of the sleeve pipe before you add the concrete mixture so you don’t accidentally plug the pipe or get gunk inside.
Carbide Drill Rock Bit
For a mold, find a cheap large bowl and invert it. A cardboard box also works as long as you support the outside, perhaps with sand piled into a larger box. Spray the mold with cooking oil first so you can slip out the concrete or peel away the cardboard later. Embed bits of broken china or tile for a decorative effect if you wish. An 80-pound bag of Sakrete High-Strength Concrete Mix costs $4.55 at Home Depot, but if that’s too much for you to lift, buy almost any kind of concrete mix that comes in a smaller bag. Just check the label to make sure it’s suitable for pouring into a mold as deep as you’re using.
To make sure you buy enough concrete mix, multiply the length, width and height of your mold in inches to determine its volume in square inches. If you’re using a bowl or other round shape, measure across the rim from the center to the edge to get the radius. Multiply that by itself three times, then by 3.14 (pi) and two-thirds, or take the no-math option and use an online calculator; find one by typing “volume of half a sphere” into a Web search engine.
Whatever anchor you’re using, be careful not to pound the support pipe far into the ground where you might hit a buried water or power line. To check on whether that’s an issue, call 811 or file an online request via the “homeowner” section of Call811.com three days before you want to do the installation.
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