We all know that drills have their limitations when it comes to the size of the holes they can drill. But what happens when you need to do some bigger wood boring?
As a teenager, I decided to replace the limp, rotting plywood back deck on an old perch boat. With relative ignorance in the way of tools, and struggling to get my junior man card, I went to work ripping out the carpet and unscrewing the now rusted fasteners. It's not a big deal to cut the new board and install it. The problem comes when I need to reinstall the base. It's bolted on, but also sits down a few inches through the 2-1/2" hole.
Looking back trying to cut that #$%&*@! Hole… what am I thinking? I started with the biggest bit in the center and then tried to work my way out with the handsaw. When that didn't work, I tried drilling holes in a circle and attaching the points with the same blunt handsaw. I did end up putting it in there, but it took MUCH longer than it needed, man, is it ugly !
If I knew what to look for with spade bits, hole saws, and self drills, I'd probably be fishing all afternoon instead of cursing and sweating. Luckily, I'm much smarter now, both with the tools and with my English. I'm here to pass on this wisdom and some help from the Milwaukee Tool and its accessories.
Spade bits will meet your smallest wood drilling needs. In fact, the smallest spade bits can be in the same range as standard wood drill bits. Commonly called spade bits (or variations thereof), spade bits are between 1/4" and 1-1/2" in diameter
Spade bits, such as the Milwaukee Flat Boring Bits, are shaped like paddles. The pointed or threaded tip guides the bit into the wood and through the cut. The sharp edge of the drill can take out small wood chips and pop them out of the hole. Spade bits up to 1 inch in diameter (and sometimes larger) are designed to be used in high speed mode. The largest spade bits usually require a low speed mode to deliver the required torque to the bit.
A good, sharp spade bit will allow you to cut with minimal downforce on the bit. You can put extra pressure on it to drill faster, but it's not necessary. Especially with larger drills, if the drill has a side handle, you'll want to use that. Today's drills generate a lot of torque, and the drill can get stuck, causing the drill to twist your wrist or elbow sorely. Some spade bits have a 1/4" hex shank that you can attach to an impact driver. Spade bits are less expensive than other wood drilling options.
When to Use Spade Bits
A spade bit like the Milwaukee Flat Bit is an excellent choice for cutting holes up to 1 inch in wood that does not require finishing. Breaking through with a shovel bit can be pretty ugly, though. If you plan to have one side as a finished surface, drill into that side and let the breakout happen on the side you can't see. Once you need to drill holes longer than an inch (and you're no longer drilling at high speed with a spade bit), it's time to look at a hole saw.
Drilling carpentry with a hole saw
Hole saws come in three basic designs. You typically use diamond grit hole saws in tile, masonry and glass applications. Bimetal works on metal and is often used in wood applications. We have found that carbide reaming knives are effective for cutting through wood. I'll focus on these next. You can usually find this drill bit as small as 1 inch. Instead, they extend all the way to about 6 inches.
The hole saw consists of two parts, the mandrel and the hole saw. Collectively, we usually refer to the whole thing as a hole saw. The arbor has a threaded coupling, and sometimes a locking coupling, around the bit that holds the saw in place. The pilot bit guides the cut. Milwaukee's Big Hawg Hole Cutters actually feature replaceable spade bits. This reduces the amount of friction against the core, which increases cutting efficiency.
Because hole saws are much more complex as a system than spade bits, they are designed to be able to change hole saws around the same arbor. This saves money. Hole saws require more torque than spade bits, so the shaft must be thicker to avoid damage. For most hole saw systems you will need a 1/2 inch drill bit.
A hole saw works by cutting off only the circumference of the hole, rather than chewing up the entire hole like a spade or Forstner bit. This can result in you needing to remove the solid core or plug from the saw when you're done.
Carbide and bimetal
Look at the teeth of a hole saw to see the difference between a carbide drill wood boring and a bi-metal universal design. Hole saws have 2, 3 or 4 carbide teeth depending on diameter. You can actually sharpen these teeth as they become dull over time. To give you an idea of the sharpening cycle, the Milwaukee Big Hawg hole cutter can drill up to 600 holes before sharpening is required. Bi-metal hole saws… well, I don't grind all those teeth. In fact, we advise you not to try it.
While you can certainly use bi-metal hole saws, they will drill 10 times slower than carbide hole saws designed for drilling in wood. Let the hole saw and drill do the work and you should be able to drill at high speed most of the time. For larger diameter holes, reduce RPM (speed) and use higher drilling torque.
When to Use a Hole Saw
Hole saws such as Milwaukee's Big Hawg Hole Cutter are great for drilling rough holes from 1" – 6". It's possible to get a bigger hole saw (Milwaukee Big Hawg up to 6-1/4"), but at this point you really need to go with a typical 1/2" drill and you'll start to need more specialized equipment.
Like a spatula, a hole saw is a rough-cut woodworking drilling accessory. Breakouts leave a rough edge where you'll need to sand or cover the finished work. Like a spatula, drill from the side you intend to use as the finished surface. This hides the breaking side.
Wood drilling with self-feeding drills
Self-feed drills typically handle hole sizes between 1 and 4 5/8 inches. Don't confuse these with Forstner bits that start as small as 1/4 inch.
Self-feeding bits have outer teeth that cut the circumference like a hole saw and radial blades that cut out the core like a spade bit. The result is a cleaner finish, which neither style can do alone. The self-contained drill also has a threaded tip to pull the drill through the wood. The threaded tips on the Milwaukee Switchblade Self Feed Bits protrude more than the threaded tips of the Forstner Bits to act as a guide and pull the bit forward. They are often favored by contractors who don't care about simply creating recessed holes.
Most self-feeding drills are constructed in a way that allows you to sharpen the radial blades. The Milwaukee Switchblade Self Feed Bits go one step further. By adding a removable cutting edge, these drills save time while delivering the same fine finish. The removable blade, like the Milwaukee blade, uses hardened steel. You still get a lot of life out of it. When they wear down instead of sharpening, just swap them out.
Like a hole saw, a self-feed drill requires a lot of torque to bite a hole. You will need a 1/2" drill bit to accommodate larger diameter shafts. If you're using a cordless model, you'll also want to keep a spare battery nearby. Only with the smallest diameter you can drill in high speed mode with a self-feed drill. You'll be doing most of your cutting in high torque mode.
When to Use a Self-Feeding Drill
Since self-feeding drills fall under the umbrella of spade drills and hole saws, it can be confusing not knowing when to use them. Forstner drills are finishing drills used by woodworkers and carpenters to clean through or recessed holes in wood. However, self-powered drills are purely about getting power through wood as fast as possible. For applications such as under-cabinet lighting, a jig and hand drill with a Forstner drill will suffice. When precision is your goal, you'll find that most woodworkers turn to drill presses that use Forstner bits and avoid self-feed bits. However, general contractors, remodelers and plumbers will be looking for the threaded tips found on the Switchblade Self Feed Bits in Milwaukee.