I’d been thinking about writing this article for quite some time, but something recently triggered me to do it now. A friend asked to “borrow my drill and a 7/16” bit.” I wanted to be a smart aleck and say something like “A high speed steel bit? A wood bit? A spade bit? A cobalt bit? What kind?????” (I didn’t, though.)
The point is that drills and drill bits are go-to items in every handyman’s tool chest, and bits are intended to accomplish one simple task – drilling a hole. However, their design and composition vary, and selecting the correct one is critical to efficiently accomplishing that goal. This month, I’ll describe just a few of the types of bits that you should have in your tool arsenal. (Trust me, there are more types than I’m showing, but these are the basic ones.)
First of all, let’s cover the simple black oxide spiral steel bit, which does a great job of drilling simple holes in wood or other easily-pierced material. These bits are inexpensive, but quickly dulled. They can be resharpened but are often just tossed away and replaced once worn out. They are easily overheated by forcing them into the material instead of letting them do their job and cutting the wood away. They are not particularly suited for drilling into metal.
High-speed steel bits look essentially like the basic ones but are made of a more durable material. They cut easily into wood but are also suited to light metals. “HSS” is usually stamped on the shaft. These are overall the “most used” set in my possession. HSS bits work well in hand-held drills but also in a stationary fixture like a drill press. If drilling larger holes in metal, it’s helpful to add a drop of oil or drilling paste at the bit’s point of contact to minimize overheating. They can be purchased with various styles of “point” but the ones I like are 135-degree split-points. Those have four cutting surfaces and do not need to have a “punch” made on the metal being drilled in order to center the bit. Ones with 118-degree points have two cutting surfaces and also work well, but are not self-centering. In metal, a prick punch needs to be done so the drill point stays where it’s aimed. Both types do a good job in a drill press as well as in a hand-held situation. These bits are often purchased with a coating like titanium that may help them last longer without dulling. This pic shows a HSS bit with the two cutting surfaces, and the gold color is the titanium component.
For drilling into serious metal (stainless steel, for example) the same style of bit can be used, but it must be made with a harder material like cobalt. Even so, there are two main types of cobalt bits, M35 and M42. The M35 (5% cobalt in the steel) is best for hand-held use. The M42 (8% cobalt) cuts even better into hard materials but is brittle and best used in a drill press to avoid any “wiggle” which might make the bit snap/break. This cobalt bit has the four cutting surfaces mentioned above:
An often overlooked type of bit for drilling into wood is the brad-point. It has an obvious center point to easily locate the bit on the target, as well as cutting surfaces on the outside edges. These bits are not for drilling into metal, but do a great job for woodworkers where accuracy is needed. They work well in hand-held drills, but their real value is in a stationary drill press.
Spade bits are designed to make “quick and dirty” holes. They chop their way through wood without any real concern for accuracy. They are well-suited for situations like making holes in wall studs through which electrical wiring will be run. To avoid poke-through splinters, it’s helpful to run a spade bit into the wood until just the tip begins to protrude through, and then finish the hole from the other side.
I like to use some specialty bits in woodworking projects where pieces will be screwed together. These bits have a profile that is essentially the same as the screw which will be used. That also makes it very easy to slightly countersink the screw head by simply drilling just a tad deeper than “flush” with the surface. Here are two different styles:
Forstner bits have a unique design, and cut a nearly flat-bottomed hole in wood. Although they have a center point for locating, it’s actually the outer edge that does the real cutting. They can be highly accurate in a drill press, and allow the insertion of things like dowels and other pinning pegs to depths greater than other bit styles because of the flat bottom of the hole.
Another specialty bit that is an absolute “must” for the handyman is the carbide bit. That’s the one to use for drilling into masonry. Carbide bits work best in a hammer drill. That drill not only spins the bit but also provides a small hammering effect that helps in the cutting efficiency. Generally, only the tip does the hard work, while fluting on the remainder of the bit shaft functions to help clear the hole.
I hope all your projects go well. Thanks for reading, and happy restoring!
Ed
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