Rotary hammer drills (also known as pneumatic hammer drills, Kango’s, or Hilti‘s) are primarily designed for heavy-duty masonry work. This work can include boring huge holes into structural concrete, ripping up ceramic tiles, and even light demolition work. They also have the ability to drill through materials such as wood, metal, and plastics.
Although regular hammer drills possess the ability to drill through masonry, the force rotary hammer drills exhibit belittles this ability. The difference is in the hammer mechanism of each type of drill. Hammer drills rely on a mechanical hammer action, whereas rotary hammer drills utilise a pneumatic hammer action.
The idea behind pneumatic hammer action is that it creates high impact force, and less wear on the drill’s internal components. It works via a small piston that is operated by the drill’s motor. This piston compresses air against a metal spring-loaded plate that exerts an immense force on the drive shaft of the drill. Each time this occurs, it is considered a blow. The speed of these blows is measured in blows per minute (bpm).
You will notice that the ‘bpm’ value of a rotary hammer drill is much less than that of a regular hammer drill. This is because a rotary hammer drill exerts more force through on its drive shaft per blow, and also because it is a much slower process.
Each blow from a rotary hammer drill is measured in Joules (J). The higher the value of this impact energy, and the higher the ‘bpm’ value is, the faster a rotary hammer drill can drill through masonry.
Rotary hammer drills feature many different components, and having a sound understanding of these plays an important part in the purchasing process. Knowledge of these parts also aids in the efficient and effective use of the tool.
The power source is the component that provides the tool with electricity. On rotary hammer drills, this is done through a wired connection to a mains power supply. In Australia, rotary hammer drills operate off mains power (240V) through a 10A socket.
Cordless rotary hammer drills that are powered by a battery and a charger are also available and bear very similar features to those described below. They are generally not as powerful as their corded equivalents and require regular charging, but are usually considerably light in weight and have unmatched portability.
The switch allows the electricity from the power source to flow through the tool. All portable drills are activated by a trigger switch. When this trigger is pressed, the drill will begin to operate. The most common is the variable speed trigger. The further you depress this trigger, the faster the chuck rotates.
This button can be pushed while the trigger is depressed and the trigger will lock on to that set speed. To cease this function, simply pull the trigger.
Make sure this button has been released prior to disconnecting the tool. If not, the tool will begin to operate upon reconnection and may result in injury. For more safety recommendations, click here.
With a flick of this switch, the drilling direction changes to allow for forward and reverse motion (right and left motion respectively). This feature is only found on some rotary hammer drills.
Rotary Hammer Drill Motors
Motors are the main component of all power tools, and are the component that converts the electricity into motion. The power that motors produce is measured in Watts (W). Motors used in portable electric drills are called AC motors (they are also known as universal or series motors).
Rotary hammer drills can have motors with an input power of between 400W and 1500W, and can weigh anywhere between 1.8kg and 12kg.
Many manufacturers will state only the input power of the drill, as this is the larger and more impressive number. This value is actually just an indication of the demand a tool will place on a power outlet under normal operating conditions. The power output at the chuck, though, is significantly less than the input power. This is due to the efficiency of the drill’s internal components, and how power is transferred through the machine. Generally speaking, higher quality tools have greater efficiency and require less input power to produce the same power output. Therefore, although it is uncommon for most manufacturers to include a power output value, it is a much better way of comparing tools.
Most professional quality tools will have a round port on either side of their housing. These ports give simple access (with a slotted screwdriver) to the most frequently wearing component of any tool – it’s brushes.
Some models also come with a soft start motor for containing the start up reaction force of the drill.
Also known as a gearbox, transmissions dictate the speed range (revolutions per minute, or rpm) that a drill can operate at, and the corresponding torque (or turning force) that it can produce.
Transmissions can contain single or multiple gears that are driven by the motor. If a small gear is used in the transmission, then rotary speed will be high but torque will be quite low. If a large gear is used, then rotary speed will be quite low, but torque will be high.
Electric drill accessories come in many different sizes, and all have a recommended speed that they have been designed to operate at. To accommodate these requirements, you must have a drill that has both enough torque and enough speed to handle the accessory.
To acknowledge this fact, manufacturers will state the maximum drilling capacities that a drill is capable of drilling into various materials. These materials are wood, metal, and masonry.
Because of this style of hammer action, rotary hammer drills do not require excessive speed to operate effectively. Therefore, they only have one gear that is designed to perform at speeds of up to around 1500rpm.
The optimum drilling capacities of drills are where they will deliver their best performance. If you halve the drill’s maximum drilling capacity, it will give you the optimum drilling size, and is the size of hole you should be most frequently drilling with that drill.
It is quite common for larger units to have a small access point to the grease that lubricates the transmission. Access to this grease is achieved via the included pin spanner. This grease should be replaced after approximately 50 hours of accumulated use.
Torque limiters (or clutches) are also quite common on larger units to stop injury to the user if the drill bit jams during use.
A mode switch allows users to choose between different drilling modes. There are two different types of rotary hammer drills, and they are each known by the number of modes they possess.
Two-Mode Rotary Hammer Drills
Two-mode rotary hammer drills are named as such for the two modes they possess – rotary drilling and rotary hammer drilling.
These drills are typically the smallest type available, but still pack more than enough punch to accomplish most repetitive masonry tasks with ease. They are also an excellent size for most wood and metal tasks (with the use of a keyed chuck adaptor).
Their two modes are illustrated by the following symbols.
This mode allows for
powerful rotary drilling.
This mode engages a rotary hammer
drill's pneumatic hammer action.
Three-Mode Rotary Hammer Drills
Three-mode rotary hammer drills can perform normal rotary drilling, rotary hammer drilling and chiselling – all with the flick of a switch. This chiselling function (basically rotary hammer drilling without the rotation) is a great option for light breaking work and jobs like bathroom renovations.
They feature two more symbols on their mode switch, and these are illustrated and described below.
This mode acts like an electric chisel,
hammering without rotation.
This mode exists to enable you to
straighten a chiselling bit before
engaging the chiselling mode.
Larger two-mode hammer drills are also available from some manufacturers. These are only capable of rotary hammer drilling and chiselling, and do not have the capacity to perform normal drilling tasks. They can exhibit up to 20J of impact energy, and can produce up to 2200bpm. They are capable of drilling up to 52mm in concrete with adrill bit and up to 160mm with the aid of a core cutter.
The chuck is the part of the drill that grips drilling accessories. The transmission powers the drive shaft and on the end of this shaft is the chuck.
Rotary hammer drills are fitted with SDS (Special Drilling System) chucks. These chucks are made out of high quality plastic, and lock accessories that have an SDS shank into place.
There are different sizes and styles of SDS chucks, but all rely on the same principles. The two most common styles are SDS-Plus and SDS-Max, and each has its own corresponding drill bits. SDS-Plus is the standard for lighter-duty models, and SDS-Max is only found on the larger and heavier units.
To lock accessories in place simply pull the chuck’s sleeve back, insert the bit as far as it will go (turning it may help it to slip into position), and release the sleeve. The bit should not be able to fall out but should be able to slip back and forth.
For standard drilling into wood and metal where a hammer drill is not required, 13mm (1/2”) keyed chuck adaptors are available with an SDS shank on them, and will slip in and lock straight into an SDS chuck.
These adaptors are not designed to support masonry drilling on these drills. Apart from the inability of the adaptor and regular masonry drill bits to withstand the forces of a rotary hammer’s pneumatic hammer action, the forces will simply dislodge the bit from the keyed chuck.
The housing of a drill is the casing that protects the internal components. Rotary hammer drills will typically have a jampot housing.
A jampot housing is where the internal components of the drill are inserted into the housing and then a lid (usually an alloy casing) is screwed down to seal it. This durable style of housing is generally used on high quality power tools, and is much more effective at keeping the internal components aligned and the power tool structurally sound.
These drills may also have anti-vibration technology built into the housing, which helps to prevent frequent users from acquiring severe conditions such as Hand Arm Vibration Syndrome (HAVS).
The handle is the component of the drill that you hold with your dominant hand and is what you use to apply pressure to the drill.
Light duty rotary hammer drills usually have a pistol-grip handle, and heavier duty units will nearly always have a D-handle.
This handle is designed to stop rotation and to provide stability for the user. It is secured just behind the chuck and can be positioned at various angles to the body. The angle is generally changed by unscrewing the handle, moving it, and screwing it back up.
On rotary hammer drills it is common for side handles to have shock absorbing capabilities, in order to quell excessive vibrations during use.
The depth stop is a small plastic or metal rod that sits in the side handle, and can be set to certain lengths in front of the drill to monitor the depth of holes.
This is especially useful if you are drilling holes where the drill cannot go through the material or if you need to drill holes of a certain depth.
When purchasing a rotary hammer drill, decide what features are most important to you (from the features above) and make sure these are included in your final purchase. The main considerations you should make include how much power you require, the size and weight of the tool, whether you need it to be cordless, and how often you will be using it.
A rotary hammer drill should really be capable of drilling the largest hole into masonry you will ever need to drill. It should also be comfortable to use, and should be of very solid construction. Remember to ensure it is a three-mode model if you require a tool for light chiselling and breaking requirements.
Manufacturers will either direct their products at the DIY or professional market. DIY tools are designed for home use and generally include plenty of features for a very modest price. They also tend to have very generous warranty periods, including replacement warranties. Professional tools are designed for commercial use and are built for durability, performance, and reliability. Their warranty periods tend to be much shorter than DIY tools, and are exclusively repair warranties. The main advantage of these tools is that they should well outlive their warranty period, and if they require repair and maintenance spare parts are readily available.
The price of any tool will depend on the quality, capabilities, and features of the model. Bear in mind that at least one of these three elements is commonly sacrificed by manufacturers to reduce the tool’s price and increase its sales. After all, price is the most important factor for consumers.
Rotary hammer drills can cost anywhere from $50 to $500.
It is important to bear in mind that the entire cost of any power tool is not just it’s initial purchase cost. Added costs can include accessories for the tool to function, maintenance, downtime, and replacement costs. Buying according to your requirements will help to keep these costs to a minimum.
The following tips will help to preserve the life of your rotary hammer drill, increase your efficiency, and most importantly, keep you safe.
- If the bit jams because the power tool is overloaded or it becomes wedged in your work, switch the power tool off immediately. Because of this, you should always prepare yourself for a sudden reaction force when drilling by taking a firm stance and holding the tool with two hands.
- You should never change the direction of drive whilst the tool is still operating, as it is highly likely you will damage the tool’s gears.
- Always wait until the machine has come to a complete stop before placing it down.
- Only use rotary hammer drill’s for short periods of time and with work gloves, as the vibrations they produce can seriously damage your hands and arms.
Personal protective equipment (PPE) must always be worn when operating power tools. For more information on PPE and power tool safety, click here.
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