hen accuracy in hole size and depth is crucial, for example, when making furniture or installing delicate trimwork, reach for a drill/driver. The control offered by a drill/driver’s clutch can be somewhat more important than the need for extreme levels of torque. However, when you need to assemble a lot of nuts and bolts, or sink hundreds of screws in short order, an impact driver is generally a much better tool to use.
While impact drivers lack clutches, a number of models incorporate power selection switches that enable you to select the maximum impact force for a particular application. This can prevent over tightening nuts or sinking screws too deeply.
Impact drivers provide considerably more power than drill/drivers, typically at a lighter weight, resulting in faster, easier drilling and driving. For example, the Makita LXDT06 impact driver weighs 3.3 pounds, has a 5″ head length, and delivers 1,500 in-lbs of torque. In contrast, a compact drill/driver, like the Bosch DDB180-02, weighs 3.2 pounds, has a 7-5/8″ head length, and delivers 400 in-lbs of torque. The Milwaukee 2603-22CT, a full-size drill/driver, has an even longer head size (8-1/2″), weighs 4.4 pounds, and has a maximum torque level of 650 in-lbs. (Note that the Makita driver is equipped with an 18V 3Ah battery while the two drill/drivers have 18V 1.5Ah batteries).
The impacting action of an impact driver generates less torque reaction, making them easier to use when setting long, larger diameter fasteners, and you’re much less likely to strip screw heads.
Unlike drill/drivers that have single sleeve ratcheting keyless chucks, impact drivers have 1/4″ hex chucks. One advantage of this chuck is that it reduces the overall length of the driver head – so that the driver fits more easily into tighter spaces. A second advantage is that it makes bit changeover much quicker.
While you’ll pay more for an impact driver, faster drilling and driving generally means greater productivity, which, over the long run, will provide you with a better return on your tool investment.
A common complaint with impact drivers is that they are significantly louder than drill/drivers – particularly in confined spaces – which can be annoying when you’re using one for an extended period of time. And, because of the greater impact stress these tools generate, you’ll need to purchase drill and drive bits specifically designed for these tools.
The extra power of an impact driver comes from its internal design. Like a drill/driver, an impact driver uses rotational force to turn its drive shaft. However, when the torque needed to turn the shaft becomes too great, a compression spring forces a hammer gear against an anvil, applying additional force around the shaft, much like whacking a wrench with a hammer to loosen or tighten a bolt.
It’s this percussive force that provides an impact driver with such raw power – upwards of 1,600 in-pounds of torque. And, greater power means that you can get more more done sooner.
Impact Drivers: What’s To Like
• High levels of power for the most demanding driving tasks
• Light weight for extended use
• Less torque reaction under load
• Shorter head length for use in confined spaces
• Super quick bit changeover
• Faster drilling & driving for increased productivity
Brushed and Brushless Motors
Brushless motors have been used in other industries for some time, but have only recently begun to show up in power tools, particularly drill/drivers and impact drivers. You can expect to see just about every power tool manufacturer adapting this technology for a wider range of cordless power tools, including circ saws, recip saws, grinders, and the like.
A typical brushed motor consists of wires, magnets and brushes. The stator is essentially a fixed magnet or electromagnet. The armature, or rotor, rotates within the stator, and is connected to a drive shaft and commutator. Carbon brushes provide the electrical connection between the power source (the battery) and the commutator, which reverses the direction of current flow to the armature so that the magnetic fields maintain rotation. And it’s that rotating force that produces torque.
One of the main disadvantages of a brushed motor is that the brushes constantly remain in contact with the armature – this creates friction (which accounts for the sparking that you see through the vent holes on a brushed power tool) and heat. Both of these reduce the efficiency of the motor. The constant friction between the brushes and the commutator wear each other down, which adversely affects motor performance – and where a motor is subject to excessive heat build-up it can lead to motor failure.
A brushless motor does away the brushes and the commutator. Like a brushed motor it has permanent magnets and electrically induced magnets (the stator). However, in place of brushes that provide the electrical connection, a brushless motor uses an external electronic speed controller that creates the revolving magnetic field between the two magnets and causes the shaft to spin. Shown below are the brushless motors on Hilti, Makita, and Milwaukee drivers.
A major advantage of this system is the reduction in friction inside the motor, which means less wear on internal components and less heat build-up, resulting in a longer motor lifespan. Because the electrical connection is controlled digitally, rather than mechanically (by brushes) brushless motors run more efficiently, transferring more power to the drive shaft. Like brushed motors, they can heat up, particularly under a heavy load. However, they can be more effectively cooled.
The brushless motors on the Hilti, Makita and Milwaukee drivers look remarkably similar (I wasn’t able to open the casing on the DeWALT). These motors are not only small, but they have very few moving parts – which means fewer things to wear out, and more importantly, less friction and less heat.
If you were to take out the brushless motor on either of these impact drivers you would see something similar to the photo below – a fan (which serves to cool the motor), a permanent magnet, an electronic speed controller (that serves the function of the brushes and commutator on a brushed motor), and an electrically induced magnet (the stator). Placement of the fan varies – on the Hilti it’s located just behind the stator – on the other drivers it’s located behind the permanent magnet.
Why Brushless is Better
• Smaller and lighter than brushed motors.
• Electronic speed controller provides increased control over speed and torque settings.
• Less friction, heat and amp draw means a longer run time.
• More efficient use of energy
• Less energy required to run the motor.
• Virtually maintenance free.
• Longer tool life.
Six Brushless Impact Drivers to Choose From
I looked at six brushless impact drivers from four manufacturers – DeWALT, Hilti, Makita, and Milwaukee. All these models come in two kit formats, each consisting of the driver, two batteries, battery charger, belt clip, and a storage box or bag. The ‘compact’ kits contain two 1.5Ah batteries (1.6Ah for Hilti), while the ‘high capacity’ kits come with dual 3Ah batteries (3.3Ah for the Hilti).
Makita was the first company to make ‘bare’ tools available – the tool body without batteries, charger, belt clip, and storage box or bag – making it more economical for users to add to an existing kit. It’s a great idea, as you can save anywhere from 40 to 55% off the kit price. Fortunately, all companies now offer bare tools.
I looked at the tool ergonomics, the features they offered, and their power and performance.
For anyone who uses power tools on a daily basis, particularly for extended periods of time, good ergonomics is important. The way a tool feels in your hand is not only affected by the size of your hand, but by the dimension and configuration of the tool handle, tool head, and battery pack. And, of course, there is still an element of subjectivity – what feels comfortable and well-balanced for one person may be awkward for someone else.
Fortunately, tool manufacturers take tool design very seriously, and are quick to introduce new design features that improve tool balance and comfort. After using these drivers for upwards of six weeks, I feel that there is little, if any, substantive difference between how these drivers feel in the hand. They are all very well-balanced and comfortable to hold, have soft-grip handles, large triggers, and easy to manipulate forward/reverse buttons. The differences in weight and head length are somewhat more apparent.
I weighed the tools with 3Ah batteries installed. The lightest drivers, the Makita LXDT01 and LXDT06, are 3.3 pounds, while the Hilti is the heaviest at 3.8 pounds. That 15% weight differential is barely noticeable, likely because these drivers are so well-balanced. Of course, all these tools will be somewhat lighter with 1.5Ah batteries installed – for example, the Makita LXDT06 drops to 2.75 pounds and the Hilti comes in at 3.2 pounds.
Head length is fairly uniform. At 5″ the Makita LXDT06 has the shortest head, while at 5-3/4″ the Hilti has the longest head. The other drivers are 5-1/4″ long. If I was consistently using an impact driver in confined spaces, head length would be a more important factor than weight – otherwise, I don’t consider the difference in head length to be critical.
With my moderately sized hand – 3-3/4″ palm width – I found that the Makita drivers and the DeWALT had just the right feel – when not wearing gloves. The handles on these drivers have a more streamlined curve – particularly at the bottom of the handle. However, when wearing gloves the tactile difference between these drivers is, in my view, not that great.
There are a number of features to consider when selecting an impact driver, including the drive chuck, power level selection, battery power meter, work light, belt clip, storage, and warranty.
|Hex Drive Chuck|
All impact drivers have 1/4″ hex drive chucks – you install a bit simply by pushing it into the chuck. To remove the bit you pull on a spring loaded, knurled or ribbed, sleeve that surrounds the chuck.
The sleeves on the Makita LXDT01 and LXDT06, and Hilti were the easiest to grasp – spring tension isn’t overly tight, and the base of the sleeve is angled, affording a better grip. I found that the sleeve on the Milwaukee required noticeably more effort to move, and my fingers frequently slipped off the chuck sleeve.
The DeWALT doesn’t have a sleeve, instead it uses a bit release button, located below head of the chuck. This was by far my favorite, as it made bit removal much quicker. Surprisingly, even with no chuck extending out the front of the casing it didn’t have the shortest head length – that honor went to the Makita LXDT06.
|Power Level Selection|
All of the drivers except the Makita LXDT08 feature three power level settings – low, medium and high, enabling you to select the right speed and impact level, so that you can better control the torque level for the job at hand. You select the power level via a slider switch (DeWALT) or an electronic pressure button (Hilti, Makita, and Milwaukee). I found that both types were quick and easy to use. For the Makita LXDT08 the only way to control torque is to feather the trigger, particularly as you get closer to sinking screw heads or snugging up bolt heads.
The power selectors on these drivers is similar to the clutch on a drill/driver. It enables you to set a maximum torque level so that you’re less likely to sink screws too deeply or shear the heads off bolts. At the low power setting the torque level varies considerable, from 200 in/lbs for the Milwaukee, 220 in/lbs for the Makita, to 500 and 530 in/lbs for the DeWALT and Hilti respectively. At the highest setting the difference is not so great – 1,460 in/lbs for the Hilti and Makita LXDT01 to 1,600 in/lbs for the Milwaukee.
The Makita LXDT06 is the only driver with a separate mode to use when setting TEK screws to prevent the screw from over tightening.
|Battery Power Meter|
I think that battery power meters (fuel gauges) are great features that should be on all power tools (or on the batteries) – especially since lithium-ion batteries deliver full power right up until the charge runs out. At the push of a button you get a pretty good indication of how much juice is left in the battery. It can be frustrating to start a job or scurry up a ladder only to have your batteries fizzle out after a few minutes.
The Hilti and Milwaukee have the power meter on the battery. Both have 4 LED lights that let you know how much power remains in quartiles (25% to 100%). I prefer this arrangement, as I don’t have to place the battery onto the tool to check the battery status. The Hilti is the most convenient in that the power meter is activated when you press the battery release tabs.
The DeWALT is a bit of an oddball – there is no power meter on the 3Ah battery, though there is one on the 1.5Ah battery.
The Makita LXDT01 and LXDT06 have the power meter on the tool body. On the LXDT06 you depress the trigger to see the battery capacity display. The LXDT01 is less useful – there is a single LED window (the red arrow in the photo below) that only flickers when the battery capacity is down to about 20%. Still, it’s much better than the Makita LXDT08, which lacks a power meter altogether.
When work lights first began appearing on power tools I thought it was merely a marketing gimmick. However, I’ve come to view them as very useful features – particularly when working in poorly illuminated or confined spaces. Fortunately they consume very little power, so have virtually no adverse effect on battery run-time.
On most drills and drivers the lights are located just above the trigger and below the chuck. I find that in this location they tend to cast a shadow above the center point of the illuminated area. But, because impact drivers lack a clutch, the chuck is shorter than on a drill, so they don’t cast as much of a shadow.
The DeWALT and Hilti have lights that surround the end of the chuck – these produced the best light – bright and widely dispersed. I found the light cast by the Hilti to be the brightest and most dispersed, though it did cast faint dark shadows across the lit surface.
The Makita drivers and the Milwaukee have a single LED light. As you can see in the photos below, all were reasonably bright except the Makita LXDT08, which cast a very weak light. In these photos the drivers are approximately 3′ from the wall. Typically the lights remain on while the trigger is depressed. However, on the Makita LXDT01 and Makita LXDT06 you can turn the lights off with the push of a button.
All these drivers come with a removable belt clip, which you can mount on either side of the tool – depending on whether you’re right or left-handed. The Hilti is the only one that has the clip mounted up towards the front of the tool, which causes the head to cant slightly away from vertical when suspended on a tool belt. None of the clips are adjustable. The clips may be shaped somewhat differently, but they all perform the same function, and I didn’t notice any substantial advantage of one design over another.
A good quality storage case protects your tool investment, and facilitates carrying it to and from a job site. All the drivers come with a lockable hard plastic case – except the Hilti, which comes in a canvas bag. The DeWALT and Milwaukee cases were tight fitting, with just enough room for the tool, charger and two batteries. The Makita case was the largest, providing storage for a second impact driver or drill, plus a few bits.
I prefer hard shell cases, as they offer better protection from dust and moisture, and safeguard the contents better than canvas. However, I did like the Hilti bag. It’s made of a heavy canvas, comes with a detachable shoulder strap, and provides a heck of a lot of storage space. There is also a convenient storage pouch on the front of the bag that will hold several batteries or hand tools. The Hilti storage bag just about replaces the need for a separate tool bag for carrying all your impact bits, hole saws, and the like, plus a smattering of other hand tools.
These impact drivers are small and light enough that you can easily carry them around by the belt clip. Still, it’s often more convenient just to set them down or a nearby surface. Bottom mount batteries give these drivers a low center of gravity, which makes them very stable when set down.
Ocassionally though, you’ll lay the tool on its side. Except for the Hilti, the drivers have one or more rubber bumpers on their sides that provide friction protection for the casing. The Milwaukee and DeWALT have large bumpers that provide good side clearance. However, I preferred the Makita drivers – even though they have smaller bumpers, they have a lot more rubber covering the sides, top, and back of the motor housing.
Impact drivers are small, and lack a side handle. So when using the driver you’re most likely to place one hand on the top of the tool to provide extra stability and control. I found that when using any of the drivers intermittently – four or five minutes at a time – heat build-up was negligible. However, when running them continuously, at high speeds, for more than about 10 minutes, they all heat up considerably. I don’t have a thermal imager, so was unable to measure temperatures – but I wasn’t able to hold onto the top of any of the drivers without wearing gloves.
Internal fans, which can be either behind (Makita and Milwaukee) or in front (Hilti) of the permanent magnet, serve to force hot air away from the motor through holes in the casing. But, more holes don’t seem to have a noticeable impact on reducing heat build-up.
The DeWALT is the only driver that provides on-board bit storage (for a single driver bit). The bit clip can be removed and mounted on either side of the driver (with the belt clip mounted on the opposite side). This is a feature you might find useful if you use your impact driver for both hole drilling and screw setting.
The Makita and Milwaukee drivers have a replaceable rubber bumper ring at the front of the tool, which provides some friction protection where the tool is most likely to encounter knocks and bumps. While the front of the DeWALT has a rubber cover, it isn’t user-replaceable. The Makita drivers also have clear plastic case covers behind the bumper rings. While they look fragile they can definitely stand up to a lot of abuse.
The bumpers on the Makita LXDT01 and LXDT06 are phosphorescent – they glow in the dark. Useful, I suppose, if you happen to leave your driver in a darkened room.
I mpact drivers can be used for a fairly wide range of nut and bolt setting and screw driving tasks. Where they really excel though, is at setting large fasteners. I did my testing on the assumption that these impact drivers will appeal primarily to contractors, renovators and cabinet makers rather than furniture makers or DIYers, with the former group likely using the tools more continuously.
To test the drivers I sank as many 3/8″ x 3-1/2″ lag screws as I could into a 4″ fir fence post on a single battery charge without predrilling, and with the driver at it’s maximum impact setting, and using 3Ah batteries. I staggered the screws to minimize splitting, and avoided any knotty spots on the posts.
I sank screws for ten minutes, let the driver cool down for five minutes, and then repeated sinking screws. I repeated this process three times, and then averaged the scores.
|Hilti SID 18-A||54|