The impact driver is another specialised power tool that has recently started to make its way into the tool kits of DIYers and tradesmen. Impact drivers were originally a manually-operated hand tool that worked by creating a sudden large turning force or torque at the head of the tool when struck by a hammer. This turning force was used to tighten or loosen stubborn screws while the simultaneous linear forward force produced from being struck ensured that the screwdriver bit was kept fully inserted in the screw head. In more recent times, as with many hand tools before it, the impact driver has become electrically-powered. In electric impact drivers the high levels of torque are now produced by the electric motor driving an internal hammering mechanism striking against the drive shaft of the impact driver.
In this review of electric impact drivers, we first look at the functionality of this power tool type, what it is used for, and how it compares to the related impact wrench. After that, we study the general characteristics of impact drivers and the features to look out for when buying one, before finishing with an examination of an array of popular impact wrenches that are sold in the UK today.
The Electric Impact Driver
The electric impact driver is not dissimilar from any other electric screwdriver or drill driver, but stands out from these other machines by the excessive amount of torque it can generate through its internal hammering mechanism. At the same time, the impact driver remains safe to use by anyone since the large amount of torque is applied so briefly at each strike of the ‘hammer’ that very little consistent reactionary force is produced. This means that there is little chance of the impact driver twisting in the opposite direction to the motor rotation, potentially injuring the operator, if the fastener binds or refuses to budge.
As a consequence of this exceptional torque, the impact driver can usually drive stubborn fasteners faster and more efficiently than any other equivalent electric screwdriver or drill driver. This makes the electric impact driver ideal for jobs with large and difficult-to-insert screws going into harder materials or in projects where a large number of long screws need to be driven home quickly.
Given how good impact drivers are at screw driving, one might be tempted to ask why bother with non-impact machines at all. The main reason is that although impact drivers work better than other screwdrivers on stubborn fasteners, the equivalent regular electric screwdriver is usually more efficient at normal unchallenging screw driving. In addition, impact drivers are louder than similar regular electric screwdrivers or drill drivers, often necessitating the use of ear protection if used frequently. And the high amounts of torque produced by an impact driver can more easily strip or cam out more sensitive screws. Finally, like impact wrenches which require special impact resistant socket sets, impact drivers also require bespoke impact resistant screw bits to withstand the high forces created by the impact mechanism. Impact resistant bit sets are generally harder to come by and are usually more expensive than regular screwdriver bits.
Impact Driver vs Impact Wrench
Impact drivers are very similar to impact wrenches in that they are electrically powered tools that use the repeated striking of an internal hammering mechanism to increase the torque needed to drive stubborn or stuck fasteners. However, impact drivers differ from impact wrenches in certain subtle ways. Firstly, impact drivers are less heavy duty and usually have lower maximum torque levels than impact wrenches. This is because the torque needed to release a stuck screw is usually significantly less than that which can be needed to release a frozen nut or bolt which impact wrenches have to contend with. Indeed, applying too much force to a screw can lead to a damaging cam out of the screw head. Impact drivers also differ from impact wrenches in their driving shanks, with impact drivers usually possessing a 1/4 inch (6.35mm) female hexagonal receptacle for different screwdriver bits while impact wrenches usually have square male anvils on which sockets for different sized nuts and bolts can be fitted.
What to look for when buying an Electric Impact Driver
The vast majority of electric impact drivers are battery-driven and, as a consequence, power is measured in voltage which partially correlates with the maximum torque that the impact driver can produce. However, most electric impact drivers in the consumer space are powered by an 18V or 20V battery so trying to differentiate between impact drivers based on this metric is usually not very useful.
Probably the most important technical specification to pay attention to when purchasing an electric impact driver is the maximum torque that it can produce. In the UK, this is usually measured in Newton-metres (Nm) and although one generally wants to go for an electric impact driver with the highest maximum torque to ensure it is able to tackle even the most stubborn of screws, it is very rare that the very high levels of torque that some impact drivers can achieve will ever be needed for screw driving.
No-Load Speed or Revolutions Per Minute (rpm)
With impact tools, the higher the speed of revolution of the motor spindle, the greater the force of impact of the hammering mechanism. This means that higher rpm on impact drivers correlates quite closely with the higher maximum torques that they can produce. However, the highest levels of torque are not always needed in every job involving screw driving, and sometimes lower levels of torque are needed to prevent damaging the screw itself or the application in which the impact driver is being used. Consequently, some manufacturers of impact drivers have designed their devices with the ability to set different maximum rotational speeds which translates into different levels of maximal torque. Impact drivers also often have variable speed triggers which can provide yet further control, albeit more approximate, over the amount of torque that is applied when tightening and loosening fasteners. Variable torque control can be particularly useful at the very start of unscrewing a fastener when the risk of damage to sensitive screw heads is at its greatest. Likewise, it is also useful during the last millimetre or so of driving home a screw to prevent over-tightening.
Impacts Per Minute (ipm)
As the name suggests, the impacts per minute metric (also sometimes referred to as ‘blows per minute’) of impact drivers refers to how quickly the internal hammering mechanism of the tool operates. Intuitively one can deduce that the higher the strike rate, the more often the peak torque is applied and the faster the fastener is driven home or loosened. In reality however, most impact drivers have such high impacts per minute speeds that one will be hard-pressed to notice a difference in the efficiency of different impact drivers with different ipm values, making this metric another relatively unhelpful one when choosing one's next machine.
As with most power tools, especially those that are used frequently or repeatedly, one generally wants to aim for the lightest possible machine that one can afford in order to reduce the likelihood of hand or arm fatigue when using it. Lighter machines are also more easily manipulated especially when working up high or in confined spaces. One other point to note here is that impact drivers manufactured by the bigger name power tool companies are often compatible with a range of their batteries that have different electrical storage capacities. In general, increasing the amounts of stored electrical energy in a battery increases its weight, so the overall weight of some impact drivers can also vary depending on the type of battery that is installed.
Impact drivers, like most power tools, are weighty bulky affairs and owners usually benefit from being able to place them in a carry case during storage and transportation. As a consequence one should generally aim to buy an impact driver that comes with its own bespoke bag or case.
Like impact wrenches, impact drivers are noisy machines often breaking the 100 dB mark. This means that the operation of impact drivers should be used with hearing protection especially if the impact driver is to be used repeatedly or on a regular basis.
Popular Electric Impact Drivers in the UK
|Einhell TE-CI 18Li|
|Black & Decker BDCIM18|
* Weight includes battery pack
** The use of different battery pack sizes changes the overall weight of the impact driver
Impact Driver Reviews
Makita DTD152Z Review
At any one time, the Makita Corporation fields several closely-related impact drivers in their power tool line up. Currently, in the UK, these include the Makita DTD152, the DTD153, the DTD154, the DTD155, and the DTD156. Here we focus on what is currently their most basic and lowest torque-rated model, the Makita DTD152Z (the ‘Z’ in the model name indicating that it is a bare tool without battery or other accessories). A key feature that differentiates the DTD152 from the other models is that it represents Makita’s only current impact driver with a brushed motor, while its other impact driver models contain more modern brushless systems.
Like most impact drivers, the Makita DTD152 has a standard 1/4” or 6.35mm hexagonal receptacle with locking ring that provides for a fast tool-free bit-changing mechanism. It has a maximum fastening torque rating of 165 Nm, which is more than adequate for difficult screwdriving, but lacks the ability to set a specific torque level, making screw over-tightening or screw damage a genuine possibility if one is not careful. This torque level is generated from an 18V-powered motor that can produce a maximum no-load speed of up to 2900 rpm, translating into a maximum impact rate of 3500 impacts per minute. Although this Makita impact driver’s torque cannot be set manually, it does have a variable speed trigger that can provide slightly more refined control over the impact driver’s power.
Perhaps unsurprisingly for a Makita-branded tool, the overall design and build quality of the DTD152 is excellent, having been engineered to be both water and dust-resistant while also containing all-metal gears for robust construction. One of the standout characteristics of Makita impact drivers is their relatively small size and lightweight designs especially considering how much power they can exert. The small stature of the DTD152 makes it especially useful for use in small or awkward workspaces, while its low weight of 1.3 kg to 1.5 kg (depending on the battery fitted), is a boon for ease of use.
Feature-wise, the Makita DTD152 incorporates an electric brake to slow down spindle rotation quickly and a useful set of twin LED work light bulbs, incorporated into the front of the machine, directing ample light to the work area. Like other impact drivers where the hammering mechanism is responsible for a lot of the noise produced by the power tool, the DTD152 is a noisy tool in use, so much so that the use of hearing protection is needed, especially if used over long periods.
The DTD152 impact driver is battery-powered using Makita’s line of lithium ion-based LXT batteries. There are several different capacity versions of the LXT battery ranging from 2Ah to 6Ah, with each battery capacity determining both the overall weight of the power tool to which it is affixed, as well as how long it can perform on a single charge. Lower battery capacities have the advantage of making the impact driver lighter and easier to handle, while higher capacity versions of the battery are more appropriate for longer periods of work without needing to recharge as frquently. Importantly, Makita’s alternative line of cordless power tools found in the UK, the G-series tools, use G-series batteries and are not compatible with the LXT line of Makita batteries.
Although regular screwdriving bits can be used with the Makita DTD152, this is not recommended. Special impact-resistant bits should be used to prevent any risk of them becoming damaged by the impact forces of the powered screwdriver. The typical damage encountered when regular bits have been used in the impact driver has been anything from bits shattering to them becoming stuck in the Makita impact driver.
Although not designed to be an impact wrench, the DTD152 impact driver can also be used with impact wrench sockets if the appropriate fitting adaptor is sourced. However, this should not be a primary reason for getting this Makita impact driver as its maximum torque level cannot handle anything more than lightly-tightened car wheel nuts. This is also especially true if the power tool is being run from a lower capacity battery that can only hold high torque levels for a very limited amount of time.
Finally, the price for the Makita DTD152Z impact driver can be considered amazing value, especially considering the build quality and power tool pedigree. However, this is only because it comes as a bare tool without batteries and other accessories. As a consequence, the DTD152Z is a great tool to add to a toolbox if one already owns Makita LXT battery-operated tools but not so much if batteries and a compatible charger, both of which are relatively highly-priced, need to be purchased as well. Notably, the DTD152Z also does not come in a carry case which makes it inconvenient to store or to transport around, nor even does it come in a branded box which may confuse some first-time buyers of bare tools who might be expecting it to arrive in more obvious Makita-branded packaging.
DeWalt DCF887N Review
If you are looking for a small but powerful impact driver, then the DCF887 from DeWalt may be the power tool for you. This DeWalt impact driver is an 18V, brushless motor-powered device with metal gears for an extra-long life. It has a maximum torque of 205 Nm, making it one of the most powerful and durable impact drivers on the market. The DeWalt machine also has variable speed, facilitated through both variable trigger pressure as well as through settable power levels, making it more controllable than competitor machines with only a single speed. This variable speed functionality makes the DeWalt impact driver useful in all manner of screw driving jobs, both in light work involving finer screws in softer woods as well as tougher jobs such as driving 4-inch screws into hardwood without predrilled pilot holes.
The DCF887 impact driver runs on DeWalt’s 18V XR (and 54V XR FLEXVOLT) Lithium-ion batteries which belong to the company’s universal battery system where a range of different battery capacities can be used across a range of different DeWalt XR-designated power tools. As a result, the DeWalt impact driver is sold both as a bare unit without any accompanying battery (designated with an ’N’ at the end of its model number) and in other configurations with batteries and other accessories.
The range of XR battery capacities run from 1.3 Ah to 9 Ah, all of which can be used to power the DCF887. However, for more taxing jobs, the power requirements of the impact driver are such that really only higher capacity XR batteries are practical, with larger batteries being able to deliver peak power for longer. The battery capacity used also determines the overall weight of the DeWalt impact driver, which can range from 1.3 kg when using the smallest XR capacity battery to 2.2 kg when the largest XR battery is fitted.
As for other features and accessories, the DeWalt DCF887 sports an integral work light that consists of 3 LEDs arranged around the axis of the impact driver’s drive shaft so as to project a halo of light over the job area. These work lights remain on for about 10 to 15 seconds after the trigger is released which can come in handy when working in darker environments. The DCF887 also comes with a belt hook as standard but does not come with a carry case in its most basic configuration (DCF887N). The machine, however, is compatible with the DeWalt TSTAK carry case system which can accommodate a range of different tools.
Perhaps unsurprisingly for a premium product, there are almost no negatives with the DeWalt DCF887 impact driver, with even the price reasonable within this tool category. However, it has been reported that some units of this impact driver have been, on occasion, delivered with excessive play in the chuck. This can have a significant impact on the ability of the machine to work on difficult fixings without damaging the screw heads in the process. As a result, this is one aspect of the impact driver to watch out for when first taking reception of the machine, as this flaw is more of a manufacturing quality control issue and ‘faulty’ units should be exchanged for the higher precision machine that one expects from DeWalt.
Overall, the DeWalt DCF887 impact driver is an excellent compact machine with a disproportionately powerful punch that makes it particularly useful when working on difficult screwing or unscrewing jobs in tight spaces. At the same time, its multiple power levels and sensitive trigger control allows it to be used in a wide range of screwing applications. So if you are looking for a powerful yet small impact driver of premium quality, then you can hardly go wrong with the DeWalt DCF887.