Which is Better, a Tapered Bit or a Straight Bit?
This choice depends heavily upon the material you are drilling into and the type of screw you will be using. For wood, the recommended option is a tapered bit, regardless of the shape of the screw, you will be using. Straight bits have typically been used for softwoods and metals, while tapered bits work on virtually every material.
Both of these – straight and tapered bits – are commonly used to create pilot holes that allow you to countersink screws and wood plugs. A pilot hole is not necessary in some cases, but for most projects, you will prevent splitting both sides of the wood.
You don’t have to drill a pilot hole, but if you are drilling into hardwoods or metal, it is highly recommended. Softwood usually doesn’t require a pilot hole, but it can help the wood not to split.
Drill bits attach to your drill with either a hex-shaped shank or the shaft fits straight into the drill. Attaching your drill bit, once you have chosen the right type, should be the easiest part.
All styles of drill bits can be used with a depth stop, a device that controls the depth of your pilot hole. This prevents you from damaging the surface of the wood from the drill side and from busting through on the other side. There are many different varieties of depth stops, from very affordable to much more expensive options.
Things to know before drilling a pilot hole:
- The pilot hole needs to be the same size as the screw body (not the diameter of the screw’s threads). However, when drilling into softer woods, you may need to go down on size for your pilot hole bit to get a better “bite” into the wood.
- You’ll definitely need to use a depth control device with tapered bits. It doesn’t matter quite as much with straight bits because they don’t tend to break through the wood quite as bad.
- The shorter the bit, the more accurate it will be, so if you have a choice between a shorter or longer bit, go with the shorter one. Shorter bits also don’t break as easily, and they are easy to maneuver in tight spaces.
Another rule of thumb when drilling pilot holes is that the smaller and harder the wood is, the more your pilot hole should resemble the screw you will use. So, if you have a tapered screw, use a tapered bit. With a straight screw and hardwood, use a straight bit.
And finally, if the screw is long and will get close to the other edge of the wood, drilling a full-length pilot hole will keep the screw from breaking through the other side. Otherwise, your pilot hole does not need to be the full length of the screw.
Most drill bits are made of high-speed steel, so they are incredibly strong. This is strong enough for wood and most metals.
Materials like hardened steel and stainless will need an even stronger bit, such as cobalt or carbide. Some professional contractors and general handymen work with cobalt bits for added strength, but carbide is mostly used for production drilling, not by the general public.
Both tapered and straight bits can be made of either high-speed steel, cobalt, or carbide.
Drill bit coatings reduce friction when drilling pilot holes and, in many cases, eliminate the need for lubricants which can damage the building material and create an inconsistent adhesion for paints and stains.
A coating can be more beneficial for straight bits since they do not have the natural advantage of tapered bits. Bit coatings can be made of any of the following:
- Black oxide
- Polished screws (aka “Bright”) – not an actual coating, but smooth for less friction
- Titanium nitride (gold)
- Titanium carbonitride (blue-gray)
- Titanium aluminum nitride (violet)
Tapered Versus Straight
At first glance, tapered and straight bits have a couple of things in common:
- Most are made of high-speed steel
- Most have two flutes on the shank
These two qualities make both types of bits suitable for many purposes.
The difference between the two is obvious. Tapered bits get progressively smaller at their tip, while straight bits maintain the same width the whole way down.
Tapered bits were initially invented and produced to work with brass cut-thread screws. These were the preferred fasteners for wood furniture, but are now used almost exclusively for metal structures. Because many of these earlier screws were threaded with a hand lathe, the result was usually a tapered screw, so a tapered bit made the most sense.
Most screws today have rolled threads, cut by a machine for uniformity and added strength since the grain goes in multiple directions. This also means that the screw stays the same diameter for the entire length of the screw.
Therefore, a straight bit can get the job done just as effectively for modern screws.
Advantages of Tapered Bits for Pilot Holes
In general, contractors and do-it-yourselfers prefer tapered bits, and here’s why:
- Tapered flutes tend to cut faster and don’t require as much pressure from the drill to get the hole started. Therefore, you have less chance of the screw slipping and ruining the wood.
- A tapered bit allows for the screw to dig into the wood deeper at the bottom of the hole, creating a firmer connection.
- Tapered bits leave behind a true clearance hole at the top of the pilot hole, which is important if the screws have threads all the way up to the head and/or if splitting is likely (as with cabinets).
However, tapered bits aren’t perfect. One thing you’ll have to watch out for is the countersink on short screws. Because the taper of the screws is more drastic, the hole won’t be completely filled by the screw and will collect dirt and other particles over time.
How to Use a Tapered Bit versus a Straight Bit
The process for creating a pilot hole with a tapered bit or a straight bit is essentially the same.
- Choose the correct bit.
First, decide if you will use a tapered or straight bit. This is a matter of personal preference.
Diameters can be estimated without measurements. Hold them both up and see if the shank can be seen between the threads. If using a straight bit, most pros recommend sizing down one size from the screw you will be using.
- While you are measuring for diameter, go ahead and determine how deep the pilot hole needs to be and add on your depth control piece.
- Measure and mark the spot where your hole needs to be. A pro tip is to mark the spot with an X using two pieces of painter’s tape to help with surface cracking.
- Use your bit or a nail to indent the wood slightly so your bit doesn’t slip when you start to drill.
- Clamp the wood together so the pilot hole will go all the way through and won’t become misaligned before you can get the screw in.
- Hold your drill perpendicular to the wood and drill slowly so you don’t damage the surface of the wood. Going slowly will also help you stop at the right depth.
The choice between a tapered or straight bit is a matter of personal choice for most people. But as long as you follow the steps above, either bit should be successful for drilling a pilot hole.
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