Anyone who uses a power drill regularly will be aware of how quickly drill bits can become dull with use. Replacing a dull drill bit with a new one is the easiest way to have a sharp drilling implement when one needs one. However, buying a new drill bit every time one becomes even remotely blunt can lead to a build-up of useless drill bits languishing away in a drawer somewhere, or worse, lead to them getting binned which is not exactly environmentally friendly!
Sharpening dull drill bits instead of throwing them out is, by far and away, the better option to solving this problem. Traditionally, drill bits are sharpened on a bench grinder freehand. However, this requires a good deal of skill and experience to get right and can make getting consistent results difficult. Fortunately, there are a range of drill bit sharpeners and drill bit sharpening aids out there that can make the drill bit sharpening process an easy affair.
In this article, we look at the common types of drill bits that DIYers and tradesmen will likely encounter. We then investigate what drill bit sharpeners and sharpening aids are available on the market to give those old drill bits a new lease on life.
Common drill bit types
There are three common drill bit types that are used by DIYers and tradesmen. These are:
Twist drill bits
Most twist drill bits are used for drilling into either wood, metal or plastic. The two most common materials they are made from are High-Speed Steel (HSS) or Cobalt Steel (usually referred to as just “Cobalt”).
High-Speed Steel or HSS bits are the de facto standard for drill bits today and are named as such to differentiate them from the old high-carbon steel bits that were the predominant type used during the mid-20th Century. HSS bits are primarily used for wood drilling but can also be used to drill into metal. However, metal drilling with HSS bits is not as effective as some specialised metal drilling ones, such as Cobalt bits. At the same time, ordinary HSS bits tend to dull quicker than their metal drilling counterparts.
Cobalt bits are steel bits with a certain amount of the element Cobalt incorporated into them making them harder and longer-lasting when drilling into harder materials. As a result, Cobalt bits are usually the preferred drill bit type used to drill into metal. The addition of Cobalt, however, makes the drill bit more brittle and vulnerable to snapping, so care needs to be taken with Cobalt bits to ensure that not too high a lateral force is applied to them when in use.
118º or 135º
Twist drill bit cutting tips can be sharpened to different angles for different applications. The two most common angles that are found in the vast majority of today’s twist bits are 118º and 135º. Somewhat counterintuitively, the 135º angled drill bit tip is shallower than the drill tip with a 118º angle and provides a better drilling surface when dealing with harder and smoother materials such as metal. Therefore, it can be generally thought that 118º drill bits are made for drilling into wood, while 135º drill bits are designed with metal drilling in mind. As a result, most Cobalt drill bits, which are generally made for metal cutting, possess the shallower 135º point angle.
One final twist drill bit-specific adaption primarily used for metal drilling is the split point. Most HSS drill bits (that are not specifically made for metal drilling) will have a regular point angle. However, metal drilling bits, such as Cobalt bits will usually have a split centre point where two different bit reliefs extend out from the tip on each side. Split points help prevent a bit from “walking” across a surface when first starting to drill (particularly important for smoother metal surfaces). In addition, the mechanism of drilling action of the split point also makes it easier to drill through harder materials like metals.
Masonry drill bits
Masonry drill bits, as their name implies, are bits used to drill into masonry materials such as brick and concrete. These drill bits invariably have a small slice of Tungsten Carbide brazed into the centre of the drill tip to produce the masonry cutting surface. As a result, masonry bits are also often referred to as “Carbide bits”. Masonry or Carbide bits will usually have a cutting surface tip angle of 132º for optimal drilling.
SDS-plus (SDS+) drill bits are essentially the same as ordinary masonry bits when it comes to their drilling tip structure. However, the shanks of SDS+ drill bits are different from ordinary masonry bits as they have to be able to facilitate the hammering action of SDS+ drills.
Brad-point drill bits
Brad-point drill bits are similar to HSS twist bits in that they are usually made from high-speed steel and are designed primarily to be used for drilling into wood. Brad-point drill bits, however, exhibit a very different tip geometry to twist bits, where the centre point of a Brad-point bit protrudes significantly (see image below). This protruding centre point greatly enhances hole placement accuracy when drilling into wood as it can be more easily aligned and kept in place at the location where the drill hole is required. Importantly, when sharpening Brad-point bits, the angle between the protruding centre tip and the peripheral cutting edge is 90º.
Drill bit sharpeners
When it comes to sharpening these different types of commonly-used drill bits, it probably comes as no surprise that different types of sharpening mechanisms are required. As a consequence, this is a major differentiating factor between the different types and brands of drill bit sharpeners that are available on the market.
The most commonly available drill bit sharpeners are shown in the table below, along with the size and type of drill bit each is capable of sharpening. Some sharpeners can handle only twist drill bits while others can also sharpen masonry and/or Brad-point bits. Therefore, it is important to know what kind of drill bits you will be using before deciding on which sharpening tool is right for you.
Drill bit sharpeners in the UK