A Beginner's Guide to Drill Bits


After watching my Drill 101 video and being a master driller, now it’s time you got up to speed with drill bits - how to use them, which one you'll need for what project, and my tips for their use with rawl plugs. If you use the wrong drill bit for a project, you could damage not only the bit (which could be a costly loss!), but also your project/wall, so it's important you learn all about them and their use!


The four most common bits you’ll need as a DIY-er are a masonry bit, a dowel bit, a twist bit, and a tile bit, however, there is a wider range of bits I will cover in this post so that you can become a pro! Drill bits from different brands of course may differ in appearance slightly but have the same main characteristics to help you distinguish between screwdriver, wood, metal, tile, and masonry bits.


Screwdriver Bits


These bits, when used in a drill, enable you to drive screws into materials (particularly wood) with ease, fast. They have a hexagonal shank which means you can usually use the same set in a handheld screwdriver as well as your drill. You’ll usually also get an extending arm in your set which means you can get into hard-to-reach spaces to drive in those screws, like when putting up shelf brackets and the drill head is too big to get the right angle on the screw.



There are also screwdriver drill bits that share the same hexagonal shank but feature a spiral twist bit. These are mostly used for creating small pilot holes and therefore usually only come in small sizes.


Twist Drill Bits


The pointed end of these bits cut through the material and the spiral length allows the material to be drawn out of the hole and keep the bit straight as you drill. They can be used on several materials including wood, metal and plastics and will likely be your most used type of bit. They come in two types, defined by the metal they are made from – HSS or Carbon Steel.


HSS stands for High-Speed Steel. These bits are primarily used when you have a job that requires you to drill through metal, though they can be used in any material, it just means they can withstand high temperatures caused by friction. Most HSS twist bits are gold in colour thanks to the Titanium nitride coating which increases their hardness and gives them an almost self-lubricating property when drilling into metal.


Carbon Steel bits are specifically made for drilling wood and should never be used to drill metal as they would just shatter.

Twist bits come in sizes ranging from 0.4mm, up to 12mm+, but are only really designed to drill small holes with not much debris output. The tinier sizes, like the screwdriver drill bits to create pilot holes, snap easily, so extra care is required when drilling. If drilling a larger hole or drilling into hardwood, withdraw the bit occasionally to remove the debris and not clog up the hole. Also, personally, when working with wood, I prefer using dowel drill bits or for larger holes, Forstner bits, as explained below.


When drilling a hole for a rawl plug, select a bit the same size as the widest part of the plug. Packs will usually tell you which size to use and even have a gauge on them so you can make sure you’re using the correct size drill bit and screw for the plugs.


Tile Drill Bits


When drilling through ceramic tile, porcelain, or even glass, a standard drill bit will not suffice and will crack and chip the material. For this, you’ll need something diamond-tipped or a bit with a spear-like point to prevent damage. Due to the delicate nature of these materials, you want to use these bits at a slow speed and light pressure. These usually range in sizes from 3mm to 10mm. When using these to cut glass, it’s also a good idea to use some white spirit on the bit and hole to prevent it from heating up.


You can also get diamond grit hole cutters in sizes ranging from 6mm to 50mm, a bit like a hole saw. These are to be used with water to prevent overheating – so keep the bit wet. You can get ones that core into the tile and cut a neat plug out too.


Masonry Drill Bits


Quite obviously from the name, these are used for drilling into masonry – so brick, concrete, quarry tiles, stone, and breezeblock. They feature a large cutting tip which helps the bit melt through the material. These are best used at a slow rotational speed to prevent overheating and can be used in hammer mode and in gear 1 for tougher jobs. You will need to pull out the bit from the material often to prevent dust build-up as this can make drilling more difficult and cause overheating. These bits range in size from 4mm to 16mm and can come in huge lengths of up to 400mm to enable you to drill through walls – for example, if you want to feed the wiring through your house’s exterior wall to power a light or even to connect a satellite dish.

Again, when you’re wanting to add a rawl plug to the hole, ensure you have drilled straight without any wobble as this could cause the hole to widen and the plug to be loose. You want to use masonry rawl plugs that widen at the end as you drive a screw-in, holding it in place. Again, you want the plug to be snug. A good way to ensure you drill the right depth, is to hold the plug against the drill bit, add some masking tape a little futher than where the plug comes up to and drill up to that point - then you'll have the perfect depth hole and prevent your plug getting lost in the hole - an annoying occurrence if your screw doesnt quite reach far enough to grip onto the plug deep in the hole. You always want your plug to be flush with the entrance of the hole.


Wood Drill Bits


It’s not often you’d need a wood drill bit for walls, as you can drive screws straight into wooden studs for a superior hold, but when working with plasterboard or on other building projects, you’ll come across a few different types of wood bits to get the job done right.


There are also other common types of wood drill bits you may come across for your projects: a countersink, a countersink with a clearance drill bit, a flat wood bit, a plug cutter, a hole saw and a Forstner bit.


Dowel Bits


These standard wood or dowel bits (spur point bits) have a sharp point on the end to help grip the wood when beginning to drill. They also have a sharp double-bladed thread which helps keep the hole straight and clean when drilling through the timber. These can be used to drill fast through the timber of any type as well as plasterboard (and even some plastics) and are mostly used for drilling holes for dowels when a clean parallel hole is required. The sizes for this drill bit range from 3 to 10mm.

When drilling through plasterboard, it’s a good idea to go one size (half a size would be better) lower with your drill bit than your rawl plug, so that it is a snug fit, for example, if you have a 7mm rawl plug, I’d use a 6.5 or a 6mm and hammer the plug into the wall. Having a loose plug will affect the stability of the object you’re fastening to the wall.


Countersinks


First up, let’s look at the two types of countersink bits. These are great for ensuring screws sit flush with the surface of the wood, particularly if you then want to hide them completely with wood filler. A countersunk hole is the neatest finish you can achieve when building furniture or putting up floating shelves. The two types you can get are a standard countersink and a countersink with a clearance drill bit attached.


The standard countersink is a cone-shaped bit that creates the conical recess that ensures a screw head sits neat and flush. These are designed to be used on soft materials like wood and plastics – never metal. They are used to countersink an existing hole so you will need to drill a hole beforehand. For a better finish, it is better to countersink a hole first and drive the spur point bit through the base of the conical recess.



A countersink with a clearance drill bit cuts out the need to change between the spur point and countersink bits by combining the two. It will drill your hole and countersink it at the same time, however, may not give you the conical depression, but a flat recess, as if you were drilling a larger hole at the top. Screws will still sit flush with the top of the material but will usually be a snugger fit.


Plug Cutter


Another way to disguise screws is to add a plug. This plug cutter bit will cut a dowel shaped bit of wood out of a scrap that you can then plug a hole you’ve just drilled using the countersink bit with a clearance drill. For this bit, you’ll need to select the right size (the inner part of the bit as this is how big the plug will be) according to the size of the hole you’ve just drilled. Once plugged, the hole should almost disappear. This makes filling with wood filler and sanding down much quicker and more seamless for painting. You can also leave it unfinished, and the plug can be removed easily if you need to have access to the screw stil,l but don’t want them on show.



Cutting Larger Holes in Wood


If your project requires a larger hole than 10mm, it’s time to reach for some heavier duty drill bits that can create you holes as big as 130mm!


Flat Wood Bit



These drill bits are great for when you want a bigger hole than the dowel bits that I mentioned only go up to 10mm. Flatwood bits go from 6mm right up to 38mm. They feature a very sharp point with two flat cutting spurs which help bore large holes through the wood by chipping the material away like a chisel as it rotates. Because of the sharp point, they don’t leave the cleanest cut, particularly at the exit point where the wood will likely splinter. To reduce splintering and leave as clean an edge as possible, put a scrap piece of wood beneath where you are drilling, clamping the pieces together tight and continue drilling right into this piece and you will need to use a high speed to use this drill bit. You can also use this bit if you don’t wish to go right the way through the wood, for example, if you’re making a tealight candle holder. Unlike other large hole wood drill bits mentioned here, you can drill at an angle with these, whereas others need to be at a straight 90 degrees.


Hole Saw Drill Bit



Another way to cut large holes in wood is to use a hole saw. These are essentially a ring of the saw blade, often with a drill bit in the centre to help guide it in straight. They can range in sizes from 6mm, all the way up to 130mm. You can buy these for wood, with a traditional wood saw jagged toothed blade, or for masonry/tile which will have a diamond tipped saw blade.


For wood, the pilot drill bit creates a hole for the saw to grip onto, and once at depth, the saw will start cutting through the material until the piece is cut out. With the cup that makes up the saw dictating the max depth you can cut out, so this is worth bearing in mind when selecting the right drill bit for the job. You also cannot create stopped holes with a hole saw, you must cut out the whole material depth. They’re great for cutting holes for taps in worktops for example. But be warned, the bit can get very hot from the friction and occasionally leave a scorch mark on the inside of the hole where the bit has essentially burnt the wood! After each hole is drilled, you’ll also need to pry out the wood plug from the saw’s cup.


Forstner Bit



Unlike the flat wood bit, a Forstner bit leaves a very clean-cut edge and are great for flat bottomed holes – like for door hinges! Also, unlike the other drill bits for wood, a Forstner bit can be used to make perfect overlapping holes thanks to the sharp points on the outer part of the bit. These bits are best for dense, hardwoods and can range from 6mm to around 80mm and give the best results when used at a low speed, as not to burn the wood as mentioned above. They can also be used to cut angled holes with a super clean edge. These are my favourite bits for creating larger, clean holes. If using a large winged-back wall plug like a Grip-It, you’ll need either a Forstner bit or a flat wood bit to get your desired hole size in the plasterboard.

When starting your DIY journey, I’d recommend at least having a good set of HSS twist bits and some masonry bits, however for more than just your basic holes in the wall, you may want to expand your collection to include the more specialised wood bits as covered above. Good drill bits are also worth investing in and should be taken care of and sharpened often as a sharp drill bit cuts better and with much less effort and gives you a much cleaner hole.

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