Poking a ⅜-in. bit into wood is simple enough. Place the bit on the mark, sight the drill from two directions at 90 degrees to make sure it is straight, and drill away. A hole in flat metal plate is simple enough, with the added step of center punching the mark to discourage the bit from wandering. The center bit of a hole saw will guide it true. But there are trickier cases, where the drill wants to wander everywhere but where you want it. They all have simple solutions.
DRILLING STAINLESS TUBING
Commonly, you want a hole drilled exactly through the center and out the other side. Starting the first hole, the bit walks off to the side. You can’t use a center punch because it is unsupported and won’t respond well to a hammer blow. You could buck or brace the reverse side with a thinly padded but heavy steel block, but you might dent the tubing or loosen the deck fittings. Coming through the other side, you face the problem of alignment; sight as carefully as you like, it never comes through perfectly square.
A V-drill guide solves both problems. Slide the guide over the bit, place the bit on the mark, slide the guide down to the tubing, and secure the guide to the tubing with a c-clamp. Add a drop of cutting oil (see “Drilling Stainless” sidebar below) and drill away. I like to start with an ⅛-in. pilot hole for larger sizes, and then re-drill once the pilot hole is through both sides. Stainless is prone to work hardening, and I can easily get enough pressure on an ⅛-in. drill to make good chips. The larger drill will benefit from the pilot hole, allowing it to cut more quickly. Finally, my V-drill guide only goes up to ¼-in., but the larger drill will happily follow a pilot hole. There are many brands from about $15 to $30.
Sailrite sells the clamp-on Drill Steady Guide for $69.95. While rock steady, it is limited to ⅛-in. bits and ½- to 1 ⅛-in. tubing. It is a nice specialty tool for railings and dodgers.
STARTING A HOLE SAW WITH NO CENTER
A common homeowner case is drilling ceramic tile using a diamond hole saw to install a shower handhold or replace a faucet. Tile hole saws don’t have a centering bit. The most common boater case is increasing the size of an existing thru-hull.
A common suggestion for the boater case is to mount two hole saws concentrically on the same arbor, the inner saw riding on the existing hole and the outer saw cutting the new hole. This assumes you have both sizes, that the new hole will be concentric with the old hole, and that the arbor will mount two saws (some will and some won’t). Alternatively, you can cut a plug (you can cut it with a saber saw—it does not need to fit perfectly) for the old hole or secure a scrap to the other side, and use that to guide the centering bit of the hole saw. For small holes, you can drive in a tapered bung to hold the centering bit. The guide scrap or tapered plug can be removed as soon as the hole saw has a good start.
A common suggesting for the tile saw (no centering bit) problem is to start the saw on an angle using very light pressure. Once a groove starts to form, you use that groove to support the saw as you slowly straighten the saw. The diamond blade is very fine and doesn’t grab when placed lightly on the tile. Of course, with bad luck the diamond saw can skate across the tile, leaving and ugly scar, a pretty strong disincentive for me. In the case of a conventional hole saw, the blade will instantly grab and jump. Monster manly couldn’t hold in place. You could try running it backwards. But there is a better way.
Cut a scrap of plywood to fit the work area. If it fits tightly against a neighboring fitting or bulkhead, so much the better, but as long as it is at least 8 inches on a side, holding it with a hand, foot, or even duct tape is be enough. Drill the required size hole through the scrap. Then place the hole in the scrap over the circle marked on the hull and secure in place. Start with a light touch and the pre-drilled hole in the scrap will guide the hole saw. Another advantage of the method is that no centering bit is needed, which is handy if there is something on the other side you would rather not put a hole in. When drilling fiberglass, keep the saw wet with a spray bottle of water; this will cool the blade, and unlike oil, not interfere with subsequent bonding.
REMOVING BROKEN STUDS
If even a fraction of an inch of the stud is exposed, cut the top off square, flip the V-drill guide over, and drill a starter cone in the stud using a drill that matches the stud and guide diameter. Remove the guide and finish drilling either with a root diameter drill.
If the stud is broken off below the surface, it is more complicated. Better screw extractor kits include drill guides that drop in the hole and center the drill. I’ve never had much luck with the extractor part on seized studs, but the guides are handy. If the threads are deep enough and the stud is broken reasonably straight, just placing the root bit in the hole can work. In a bind, I have made a guide from a short piece of the same stud, clamped in a drill press vice and drilled for a pilot bit. I then cut it short length and threaded it into the hole, using it as a guide for a pilot hole.
If you are perfect you might be able to pick the threads out with a tap and reuse the hole. More likely, you will be installing a Helicoil.
Stainless has a well-earned reputation for being hard to drill. Because of its high nickel content, it work hardens if it gets hot. At first you are drilling away, then the chips stop, the bit starts to squeak, and you are done. The bit dulls and even a fresh, sharp bit may not push through the hardened surface you created. To avoid this you must keep the bit cool (lubricant and low speed), use a sharp bit, and keep enough pressure on it to make good chips constantly. Lubricant and coolant. Oil will reduce friction and heating. Specialized cutting oils containing sulfur or chlorine further improve cooling and extreme pressure lubrication. But my favorite is the water soluble cutting oil, Anchorlube All-Purpose Metalworking Compound. It costs $16 for an 8-oz. squeeze bottle. Slow down. Heat is your enemy. You also don’t want to exceed the speed where you can keep enough pressure on the bit to make good chips. With a cordless drill, the slow speed is best. If you feel the drill speed up or if chip production slows for even an instant, stop and figure out what you are doing wrong. Slower is faster, if it avoids hardening the steel, ruining the bit, and either scrapping the part or spending time and money on new high dollar drills trying to push through the hard spot. Pilot hole. Unless you are using a drill press and can maintain the pressure and cutting rate required by bigger drills, use a nominal ⅛-in. pilot drill first (adjust slightly to the size of the final drill). By removing the center, the larger drill will cut more quickly and will require considerably less pressure to keep cutting well. Sharp drill. Unless the hole is quite small and you are drilling with a press, start with a new cobalt drill. The harder the better. And remember that your fancy new drill can be ruined before the first hole is finished if you forget about cooling, lubrication, going slow and keeping the pressure on. Drill press. This is always best, since you can apply firm pressure, drill straight, monitor the progress, and apply coolant/lubricant with your free hand (clamp the work in place). Bits will last longer and breakage is reduced. If you do any metal work, a drill press and bench grinder are your primary shop power tools. 
Using a Sharpie. Hold the marker at 90 degrees to the surface. Fail this and the mark will be off. If the hole is larger than the marker, work it in a circle while still holding it carefully vertical, so that it traces the edges of the hole. You will later mark the center of the circle, perhaps using a scribe. Using a Drill. Need greater precision? Drill very lightly, just enough to make a mark, using a drill the size of the hole in the hardware, not the fastener. Then remove the hardware and drill using the proper size. But sometimes there is not enough room for the drill. Using a transfer punch. The best method for metal or wood is a set of centering punches, with diameters that match the size of the hole in the fastener you are trying to install. For gel coat, either keep the punches razor sharp and wobble slightly (it will make a scratch), tap lightly, or place a dab of contrasting paint on the tip. Still not lining up? Drilling oversized is one option, but don’t go crazy. Another handy tool when there are multiple holes is a tapered punch. Place it in one of the holes, lever it around until one of the fasteners goes in, and then move on to the next. If there are three or more fasteners and they are properly drilled, this works every time. This is how iron workers pin girders in place to insert the bolts without risking their fingers.
Tapping threads is not difficult, it just requires concentration and following a few simple rules. Drill the hole straight using the correct tap drill size, which roughly matches the root diameter of the bolt (the diameter at the base or root of the threads). Look up the size for the bolt diameter, thread standard, and material. You can usually get close enough with a 1/64-in., stepped drill kit. Lube the full length of the tap, place the guide over the hole, and twist the tap with considerable down pressure at the same time. You should feel the threads catch within one turn and catch well within two revolutions, after which you can ease up on the pressure. With most materials you should back the tap out ½-turn about every 2 to 3 turns to break the chips to prevent jamming and thread damage. In thin metal and spars, you can generally skip this step, since they fall through. In deeper and blind holes, it makes sense to back the tap out entirely every 5 to 8 revolutions and blow all of the chips out using a small hose. Poking the chips through the flutes with a stiff wire works for thick plate. The rules for dies (external threads) are very similar, though poking the chips through with a wire is preferred to running the die off. I don’t use dies often; it is normally simpler and often cheaper to buy an over-length bolt you can cut to size. Sometimes dies are used to “chase” damaged threads, but a thread file is often handier in larger sizes and has the advantage of not removing material. See “File Away You Pipe Thread Problems.” Summary. An extension of “measure twice, cut once” is making sure you cut exactly where you measured.
Thank you for the excellent article! Having acquired an 18 year old boat a couple of years ago and almost never hiring out for repairs and maintenance I have struggled with several of the things you mention here. The methods you discuss are sure to help me on future projects. FYI, I figured out the method of using a drilled scrap of plywood as a template to drill a larger hole while replacing my deck mounted windlass switches on my on. I was very proud of the results! You definitely have to be resourceful if you own an old boat and are not wealthy.
The Sailrite guide looks suspiciously like an electrical ground clamp meant to attach a ground wire to a water pipe. Amazon has one for $7. Search “ground clamp for wire”. Not exactly the same.