Author’s note: I originally wrote this almost a decade ago when, in the nascency of our relationship, my partner asked me which drill they should buy. The information below is now somewhat out of date as the field of battery powered hand tools has advanced tremendously since then, but I will note my partner still has the same drill and it’s goin’ strong.

From time to time, people ask me what kind of cordless drill they should buy. After sending a couple lengthy emails I decided to post a writeup.

One of my main reasons for writing this post is to preach the holy gospel of the impact driver. Many of us grew up driving screws using a drill, but things have evolved and specialized. Drills are better for putting holes in things and impact drivers are better for driving screws and such.

Torque, cam-out, and impact drivers

Drills work by applying continuous torque to a driver bit or drill bit. Torque is a function of power where power = torque * RPS (RPS is like RPM, but with Seconds, because SI). This is a useful thing to remember while riding your bicycle. As you probably know, lots of drilling/screw driving operations should be performed at a certain speed, so your available torque is limited by the amount of power the drill has.

However, no matter how much continuous torque you can deliver, philips-head screws are specifically fucking designed to cam out which is terrible and makes drills non-ideal tools for driving philips head screws in most cases. There are, of course, different kinds of screws which seek to address this, but that’s another post.

Impact drivers are magical devices that just became popular in the last 10-15 years or so. Impact wrenches have been around forever in both electric and pneumatic versions. You know the “braaap braaap braaap” sounds that you hear coming from the car mechanic’s garage? That’s a pneumatic impact wrench.

Both tools operate under the same basic principle, using a splined shaft to drive a pair of “hammers” that apply sudden massive amounts of torque (in the neighborhood of 1300in*lbf, that’s 150N*m for you metric folk) in shorts bursts.  Someone, who in my opinion should be canonized, figured out that you could take the impact wrench and miniaturize it for driving screws. The practical upshot of this is that impact drivers basically eliminate the cam-out problem and drive the everlivingfuck outa screws and the like.

Fucking batteries, how do they work?

In the olden days, Dewalt and most other manufacturers ran on NiMh batteries which run at a 1.2V cell voltage, lending themselves to 12V (10-cell), 14.4V (12-cell) and 18v (15-cell) product lines. Dewalt also makes/made 36V/48V battery powered tools, but we’ll leave those out of this discussion as they’re very expensive and total overkill unless you’re a contractor. At home I have a 14.4V Dewalt drill and impact driver set that runs on NiMh batteries. At the time, 14.4V was the low-end pro stuff, and happens to be totally enough for everything I do at home. They don’t make 14.4V stuff anymore.

Dewalt and other manufacturers are moving everything in the direction of lithium ion, which is great because you can get more current (amps) out of the cells and they’ve got far greater power density, but this presents an unfortunate marketing problem. Lithium ion cells run at 3.6V; run three high c-rating LiIon cells in parallel and you’ve got a fuckload of available amps in a tiny tool. However, this is only 10.8V, which is a smaller number than 12V and back when everything was NiMh this was a Bad Thing.

Dewalt still makes 18V LiIon batteries (3.6V x 5 cells) which fit in their old 18V product lines. It presents a interesting tool balancing problem due to the differing power density/weight distribution, but I haven’t noticed any adverse effects.

To compensate for the cell voltage, Dewalt started futzing with their batteries and introduced the 12V MAX and 20V MAX lines, essentially these are 10.8V/18V batteries that measure 12V/20V when not under load, but once you start using them they drop down to 10.8V. I don’t know exactly how this works but it sounds like a load of marketing horseshit. Other manufacturers have been forced to follow suit.

Marketing horseshit aside, the 12V MAX line is a lot slicker and probably more powerful than the 12V NiMh stuff which was mediocre at best. They changed a lot of stuff, including the form factor of the batteries. I bet the impact driver is fine, but would be suspicious of the drill and circular saw, but could be swayed.

I’ve tried the 12V MAX drill and impact and they’re Pretty Good for most home stuff, but if you’re going to be using for any semi-serious projects, get the 20V stuff.

Ok, but you still haven’t told me what kind of drill to buy

The short answer is get a Dewalt, unless you only need an impact driver and no other battery powered tools EVER, in which case get the 12V Max Makita impact because it’s cute, cheap, very light weight and drives up to 3" screws no problem. However, the other tools in the Makita 12V Max system kinda suck.

The answer isn’t as simple as, “get a Dewalt!” because Dewalt of the whole 20V MAX vs 18V conundrum.

At my previous job we had a lot of the NiMh 14.4V Dewalt stuff, but at some point, the 14.4V drills weren’t cutting it.  Remember my previous note about continuous torque? Turns out it’s actually really important for drilling large holes. We bought the cheapy 18V drill (two speeds instead of three, no hammer drill setting) and it was just OK. The newer 18V drill with three speeds and a hammer setting is fucking awesome. Also it will take 1/2" bits which is a boon.

For a sculptural installation I did in Hong Kong, we needed to buy a bunch of new battery powered tools as all of our existing battery powered tools were tied up in the Kafkaesque bureaucracy of Indian exit customs. I was faced with the decision of 20V MAX or the older form factor 18V LiOn. I decided to go with the old form factor LiOn stuff for a few reasons:

1. At the time, they didn’t make every tool in the new form factor (this is improving). For example, we needed to buy a battery operated portaband and this was only available in the 18V model.
2. We already had a few 18V tools, namely a jigsaw (which kicks ASS, by the way) and the lackluster two-speed drill.
3. I was wary of the gimmick.

I ended up buying a 18V drill, portaband and circular saw. The 18V LiOn drill and circular saw kick their 14.4V cousins’ asses.

The impact drivers at my previous job are probably still the 10.8v Makitas, which are adequate, but not awesome. I sold the shop on impact drivers over drills by bringing in my 14.4V Dewalt impact for a couple of months and then taking it away. We needed small lightweight impacts for a specific project and settled on the Makitas. The batteries run down fairly quickly (maybe 20-30 screws) and the torque isn’t great, and if you’re driving something bigger than a 3" drywall screw they’re useless. Bosch also makes a tiny, light weight impact driver but it is more expensive. My 14.4v Dewalt still wins over the Makita in this category.

In talking to other tool nerds, I’ve been led to believe that the 18V Makita impact drivers are superior to the Dewalts, but this was Makita’s only real advantage. Their drills and other tools still don’t measure up. Only useful information if you plan on doing a lot of screwing, I suppose.

In summary, when considering a battery powered drill (or impact driver), consider the tool family you are buying into. If you only ever want to drive screws and drill holes in things, it probably doesn’t matter, but there are a lot of really great battery powered tools out there. The batteries for these tools are very expensive and always proprietary, so once you start dropping money on battery powered tools, you’ve basically married into that tool family.

A quick note on brushless DC motors

In the last couple of years, Dewalt and other companies have started offering brushless DC motors in their tools. Brushless motors essentially use a micro controller to control the electromagnets instead of carbon “brushes” that contact the rotor. This results in a lighter, more powerful motor with less maintenance.  This is pretty cool, but it’s a bit new (and expensive) and I haven’t used any of them yet.