Having recently reviewed both the Makita DHP482Z hammer drill-driver and the Makita DTD152Z impact driver, we thought we explained the intricate differences between a drill and an impact driver - two power tools that have very specific and very different functions.
A drill as it's name would suggest, has a chuck to (originally) accept drill bits to drill holes. Drills can also be split into a sub-category of impact and non-impact drills - such as the Bosch GSB 120-LI with impact function and GSR 120-LI without the impact function. While an impact driver basically 'drives' nuts or bolts into a variety of materials - usually tougher materials such as hardwood, concrete and can even be used in mechanical repair applications.
Chuck and clutch.
Apart from a three-jaw chuck, a drill also has a clutch mechanism, a high and low gear select and depending on whether it's an impact or non-impact drill, two or three mode selector collar. All these combined to allow the user to drill in high-speed soft materials such as wood or plastics, drive self-tapping screws into wood or steel, or even drill masonry or concrete with the impact drill function. The drill chuck is also able to hold bits from 2mm drill bits, 6.35mm (1/4-inch) hex bits, right up to 13mm metal or masonry bits or 38mm wood drill bits.
1/4-inch hex collet vs 3-jaw drill chuck.
An impact driver does away with the 3-jaw chuck in favour of a hexagon-shaped collet that accepts 1/4-inch (6.35mm) hex bits. By comparison, the 3-jaw chuck, as its name would imply, only has 3-points to transfer torque to the bit while the hexagon-shaped collet transfer torque on all six sides of the bit. That's another reason why you rarely see drills with torque ratings exceeding 120Nm while impact drivers typically go past 200Nm.
Clutch vs power modes.
The impact driver however does not have a clutch mechanism, with the exception of the newer brushless models, such as the Hitachi WH18DBDL2 or Makita DTD148Z cordless impact drivers, that have electronically-controlled power modes including a self-tapping mode that is able to stop when it senses a higher load and stops when the screw has bottom out on the workpiece.
Hex-shank and round-shank bits.
Compared to a drill, impact drivers are pretty much stuck to using 1/4-inch hex bits. However, that hasn't stopped the majority of tools and aftermarket manufacturers from coming up with various adaptor bits that extends the capability of the impact driver - such as a 1/4-inch hex to a 1/2-inch square adaptor which allows you to extend the capabilities of your impact driver into a lightweight impact wrench.
To make things just a little bit more interesting, a drill chuck can also accept 1/4-inch hex bits and with the clutch set accordingly, drive bolts or nuts. Similarly, with the proper 1/4-inch drill bits, impact drivers can also be used to drill holes - the downside is the hex shank drill bits can't be bigger than 6.5mm.
So what should I get?
Ideally you should have one of each if your job demands it - which is why some tool manufacturer are bundling both an impact drill and a impact driver in their cordless combo kit. However if you're a hobbyist on a budget who just needs a go-to rotary tool, then the best option is to go with an impact drill-driver preferably with a 10mm or 13mm chuck.
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