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Consumables - Drill Bits (back to index)

A Bit About Drill Bits

Strange to see them under consumables? Not really because drill bits need to be in good condition to perform the task properly, and not many diy'ers are geared up and willing to spend time maintaining them. It is in fact easier to treat them as a consumable and purchase packs of common sizes, then discard the old bit when it loses its effectiveness.

More importantly, be sure to purchase the necessary drill bits for each job as your effort will be reduced, the quality of work improved and the satisfaction enhanced. Drilling a small hole and filing it out to take a recessed ceiling light is 'so yesterday'. You'd never see any of the glitterati doing it.

Two words of caution with drill and bits:

  1. You should turn the drill off before changing a drill bit, because accidentally hitting the trigger can cause extensive injury, particularly with keyed chucks, and
  2. Drill bits, particularly larger diameter ones, can grab and with a powerful drill almost throw you off a ladder, or cause injury to your arms at the very least.

Drill bits come with a number of shank designs (the end that goes in the drill chuck) and you need to select the right type:

Normal (Smooth) Shank

This is the most common type, and fits most common drills, except those with non-standard chucks, like those listed below.

If you need a larger bit than your drill's chuck can manage, tapered drill bits are available with a smaller diameter at the shank, but be careful as you can now overload your drill more easily.

SDS, SDS Plus & SDS Max

These are specialist drill chuck styles, that you should consider if carrying out larger jobs. In particular, from the range, SDS Plus is probably a good diy selection. Click here to see more about Drills.

Square section

Drill bits with a tapered square tang on the end of the shank are generally designed for use in brace drills. While still common, and quite a pleasure to use not least because you do not have to drag an electrical flex everywhere, most diy'ers today will use power drills.

Below we cover the more common types of power drill bit and their general usage.

High Speed Steel (HSS)

This is the most common drill type, a twist drill, designed to cut metal, but very forgiving in a lot of other materials. They are a relatively slow cutting effect and have poor accuracy if not used carefully.

General usage is steel, most metals, timber and plastics. Use on low speed setting, if your drill has one, for steel. Always centre punch metal where you want to drill before drilling, as this will stop the bit wandering. For larger holes do drill a smaller pilot hole first and work up to the final size, as large bits tend to skew the hole location. Centre punching need not be extreme, as even the slightest indent will line up the drill bit. Use high speed setting for timber to get sharper holes.

Masonry Bit

Another variation on the twist drill, this bit comes with a hardened, blunt cap, and is suited for what is collectively referred to as 'masonry'. It relies on a percussion or hammer action (dependent on your drill type) to pound the bit in as its turns. Accuracy is not high, and the bit can wander as it encounters variations in material strength. Note that even though it might be difficult to see in this photo, the diameter is set by the cutting tip, not the shank. It is best to read the diameter printed on the drill bit.

Use on bricks, concrete, rendered walls and tiles, but for wall tiles try first with percussion off, as tiles can chip very easily. For some floor tiles check regularly as the masonry bit can overheat and melt. You may encounter steel reinforcing when drilling some concrete surfaces, and it could be necessary to switch to a steel bit to adavance the drilling.

Below, everyone's idea of action - a metre long masonry bit in a rotary hammer drill!

Timber Bit

A twist drill that starts with a screw style to centre and hold the bit, then follows up with almost a wood turning action that literally cuts its way through the timber. Very fast cutting effect and good accuracy. Generally hole size is limited to about 25mm.

Use in just about all sorts of timber, but be careful not to oveload the drill or jam the bit on some hardwoods. Generally use drill on low speed setting and regularly withdraw to clean the timber out of the valley in the drill's twist. Once you start with these bits you are committed, and at high speed the bit will bite further while stopping. It is often evene necessary to hand turn the chuck to disengage the bit from the depth of the hole.

Also take care not to splinter the exit hole by drilling too fast.

Dowel Bit (timber)

The last of the regular twist drills, this bit is designed to cut a neat, near flat bottommed hole for inserting dowels (short pieces of timber) into adjoining timber panels. Also good for drilling precision holes, as these bits tend not to wander like the normal high speed steel (HSS) bits that most people use. Generally hole size is limited to about 12mm.

Use in MDF, soft and hard woods and chipboard, with a template to afford greater accuracy.

Spade Bit (timber)

Spade bits have a central point that guides the bit, followed by two gouges, one on each side, that literally slice their way through the timber, and are particularly suited to medium size holes, up to 38mm diameter or so. The beauty is that if you back off, the cutting action will cease while you think about it, and restarting is simple. Accuracy can be poor.

Use in most timbers but be careful on veneered doors and the like, in case of excessive splintering. Take great care to line up your angle of attack, as you may be drilling a a 150mm deep hole for a door lock, and a slight error at entry can see you coming out the side of the door. No real hints here, except make sure the door is secured (not wobbling) and get someone else to check you are holding the drill level (you can check the sideways aspect from above). Best to practice first on some scrap.

SDS Bits and Chisels

Shown here for comparison purposes are two chisels and a masonry bit designed to fit an SDS Plus chucking system. You can see slots in the end of the bits, two short on opposite sides, and two longer on the alternate sides, that click into the chuck.

The drill bit will work satisfactorily in a normal or percussion drill and chuck, but the chisels will not. Why not?

Because rotary hammer drills that take chisel bits have a drill stop function, that stops the chuck spinning, and delivers the impacts only, whereas you cannot turn the rotation off with normal or percussion drills.

SDS Plus to Rotary Conversion

If you do have an SDS Plus chuck, these drills often come with an adaptor that enables use of normal twist drills in the SDS Plus chuck.

Note the SDS slots on the shaft. The convertor is a simple click fit, and the twist drills are held using the hand tightening chuck.

Hole Saw (timber)

These come in a range of styles, but best style is a mandril that takes a range of blades. For quick easy jobs, some of the multipacks that feature a set of circular blades on a base are quite good and very cost effective. Accuracy is usually very good, due to the drill bit on the mandril or base that sets up a pilot hole. These handle larger holes up to and beyond 100mm. You can also get 'coring bits' for cutting holes in masonry.

Use in most timbers, though hardwoods can overload the drill, leading to burn-out. If the drill appears to slow down, then back off. Also very good in plasterboard. Removing the cutout piece from the blade can be a drag, but you'll find a way. Remember though, your first cut is the last, as you cannot line up for a second attempt once you have removed the core, so after the guide drill has entered, check that the entire face of the saw engages simultaneously - if not, you are likely cutting at an angle. One idea to save splintering on thick material is to cut half way, then line the drill bit up on the other side (using the pilot hole which should be through by now) and cut in from the that side.

Countersink

Allows you to insert a screw such that the head finishes flush with the timber surface. Metal countersinks are also available.

Used in most timbers, but generally perform the countersink first and then drill the hole after for a smoother finish. Applying the countersink after the hole is drilled can lead to 'chatter' and an irregular shaped hole. Depth should be either of two choices: equal to the screw head, or slightly blelow the surface to allow wood filler to be applied.

Please be advised: gapfilla.com does not purport to be an expert in all facets of diy, but has significant experience in almost all of the topics covered on this site. We suggest that all persons take adequate care in the translation and application of this content to their projects, particularly as projects rarely encounter identical issues and constraints. If in doubt, we suggest you seek advice from a professional tradesperson or advisor. All material copyright gapfilla.com 2005-13