18-Volt Cordless Circular Saws

I last tested cordless circular saws for TOOLS OF THE TRADE five years ago. The story back then was that the introduction of lithium-ion technology had helped battery-operated saws become more useful on the job site, but there were few standout tools in the 18-volt class. The higher voltage (28- and 36-volt) saws were the way to go when cutting framing material; the smaller tools seemed better-suited to trimwork and other light duties.

Fast-forward to today, and you’ll find that the category as a whole has improved greatly. Except for our favorite 18-volt model in the last test (Makita BSS610), the saws tested are new designs.

All but one of the kits came with their brands’ highest amp-hour (Ah) lithium-ion batteries. The Bosch shipped with 2.6-Ah batteries, but we tested it with 3.0-Ah batteries — because we tested the other tools with the best batteries available at that time. DeWalt makes two 18-volt saws; the more recent model takes slide packs, and the earlier model takes tower-style batteries. The earlier tool comes with a lithium-ion pack but can be used with the brand’s very popular nicad batteries, so I tested it with both. Hilti’s battery pack contains extra cells, so it’s actually a 21.6-volt tool; I included it because it’s the same size as an 18-volt model.

All the tools in this test have 6½-inch blades, 50-degree maximum bevel angles, and electric blade brakes. Every manufacturer supplies its own blade, so to even the playing field I equipped every saw with an 18-tooth Irwin Marathon blade.

BLADE-LEFT DESIGN

With the exception of two standard-format sidewinder models (Porter-Cable and Ridgid), the saws I tested were blade-left models — a curious trait when you consider that corded sidewinders typically have blades on the right. This aspect of the saws makes them handle a lot differently than their corded counterparts and takes some getting used to. While gaining a clearer view of the blade, you also gain a face full of sawdust, at least in right-handed use. And the weight of the saw sits on the “drop” side of the material being cut, so it requires more careful balancing to make short or shave cuts without tilting the blade.

BASIC FEATURES

All the saws have a comfortable grip with rubber-coated rear handles; where they differ in comfort is in the operation of their trigger-lock safeties. Tools that require you to push inward on a release button (Bosch, Kobalt, Porter-Cable) feel clumsier to use than ones with release levers you push straight down on. A button requires you to move your thumb, which loosens your grip on the tool slightly, whereas pushing a lever down is part of a good gripping action.

Saw stability is important, too. On most circ saws, the connection between the motor and base is in line with the blade housing; pushing down on the handle tends to tilt the motor, binding the blade and robbing the tool of precious battery power. This is less likely to happen when the connection point is in line with the handle. Only the Hitachi has this configuration, though several other saws were just as stable (see spec boxes starting on page 32).

I liked some of the extras on these saws: Six models had battery fuel gauges and three had headlights. I was less impressed with the laser line pointer on the Porter-Cable. I have yet to find a good use for this gadget on handheld saws — other than pointing the saw straight at the DIY market.

PERFORMANCE FEATURES

Certain features — common to every saw — have a major impact on performance. Here are four that, depending on how well they work, can make the difference between a good saw and a great one.

Guard

The guard should operate smoothly at all blade depths and cutting angles; the shallower the blade is set, the better the guard usually works. Hang-ups that require holding the guard open with one hand are a nuisance, especially when you’re using the saw with one hand and holding the material steady with the other.

It should be easy to accurately set the depth-of-cut and bevel angle. Large levers or knobs with a sturdy locking feel are preferable to smaller ones, and precise engraved markings in one-degree increments on the bevel quadrant help in dialing in the exact angle needed.

Cut-line marker

For fast and accurate cutting, the marks on the front of the saw base should be perfectly aligned with the actual blade kerf for both 90- and 45-degree bevel cuts. Since the saw’s body-to-base connection cannot be adjusted, inaccuracies in these notches are best corrected with a little filing. For the greatest accuracy, mark the exact width of your blade in ink just behind the notch; that way, you can easily cut to either side of a marked cut line.

Blade visibility

It’s not always possible to see the cut-line marker from all cutting positions, so you have to be able to see the blade. Because I tested mostly blade-left models, I found the blades to be well-exposed (during right-handed use) — but a few of the tools have top guards or guard-retraction levers that are low enough to obstruct the view of the cut when the saw is set to its maximum cutting depth.

PERFORMANCE TESTING

With cordless circ saws, it ultimately comes down to power and runtime. Every one of these tools can cut trim and sheet goods. They can cut dense framing materials, too — though in some cases you have to cut slowly to get through. When pushed hard in dense composite material, a few of the tools stalled so frequently they were hardly worth using. Only a handful proved capable of cutting everything on site without either slowing down or requiring a lot of babying.

As for runtime, batteries had better pack enough juice for at least half a day’s work. And even then, the kits with only one battery will have to be charged while you’re eating lunch. Don’t expect to replace a corded saw at the cut station of a framing job with one of these saws — but with the best able to crosscut 68 sheets of OSB on a single charge, you may be surprised at how much a battery-powered saw can do.

To compare the performance of the 18-volt saws with that of more common job-site tools, I included in my power testing a new 15-amp corded circ saw (DeWalt DWE 575) and the 36-volt model (Bosch 1671) that won the last two tests in TOOLS OF THE TRADE.

Power is even more important than runtime. No one wants to use a tool that struggles to do the job. To get a sense of the tools’ relative power, I timed how long they took to do the same amount of work; the more powerful the tool, the less time it took. The main test involved cutting across 4 feet of industrial particleboard (chosen for its uniformity and high density). I began with ¾-inch material — and when that didn’t challenge the saws, I created a 1 3/8-inch test blank by adding a layer of 5/8-inch particleboard.

For precise cut times I used a homemade timing device. It consisted of two micro-switches that I’d embedded 45 inches apart in a straightedge and wired to an electronic stopwatch. The stopwatch started when the saw base hit the first switch and stopped when it hit the second. The 45-inch spacing allowed me to measure cutting speed under load with the blade fully engaged, which eliminated variations caused by the blade entering or exiting the material.

I pushed the saws as fast as they could go without excessive straining or shuddering. If I went too fast, they stalled — the blade stopped with the motor engaged, or internal circuitry cut power to the motor to prevent it from burning out. Whatever the cause, it forced me to slow down. Some saws stalled so easily in the material, I could record only one or two uninterrupted times in a dozen tries. The best saws cut smoothly every time, slowing when pushed harder but never stalling (for power and runtime test results, see charts on page 30).

The last time I tested cordless circ saws, I timed how long it took to cut through homemade 2×12 LSL (a four-layer stack of 7/16-inch OSB 11¼ inches wide). I repeated that test with these saws to see how they compared with previous models. In the earlier test, some 18-volt saws could not make it through this material. Now even the weakest 18-volt models struggled through, and the strongest sailed through faster than the best 36-volt models.

Runtime

I tested runtime by counting the number of cuts it took to deplete each tool’s batteries. I made the cuts across the 4-foot side of doubled-up 7/16-inch OSB, with each cut counting as 8 linear feet. To avoid overheating, I made them at a moderate pace in groups of 10 before resting the saw. All but the Ridgid and Porter-Cable were able to make that many cuts without overheating.

There are still a lot of saws in the 18-volt category that are too weak and slow to cut all framing materials reliably, but the standouts can hold their own against bigger and heavier 36-volt models. They may even bump corded saws out of the hands of builders on occasions when a day’s worth of gas would be burned to power saws with a generator.

The Milwaukee saw is clearly the best of the bunch, with winning times in both power tests that eclipsed even the champion 36-volt saw, and with excellent runtime. The DeWalt DCS391 ranks second, placing just behind the winner in both power tests, and with very good runtime.

The DeWalt DCS390, the Bosch, and the Hilti occupy the next tier down and stand out in different ways. The DeWalt placed third in the power tests, and the Hilti and the Bosch led in runtime.

Makita’s saw rated just above both the Hilti and the Bosch in power, but its lower runtime bumps it down a notch. Still, its ample power, compact size, and great features make it a solid trim saw.

The Kobalt and Hitachi saws are relatively weak, though they posted good runtimes. The Ridgid — despite many nice features — is held back by its tendency to stall, while the Porter-Cable tool is simply outclassed by the competition.

Michael Springer is the former executive editor of TOOLS OF THE TRADE.

Thanks to Irwin for supplying the saw blades used in this test.

BATTERY VOLTAGE EXPLAINED

The full-size battery packs that come with most cordless circular saws contain ten 3.6-volt lithium-ion cells. The cells are wired in series (connected end-to-end, as in a flashlight) in strings of five, and then wired to each other in parallel. Battery voltages are additive when cells are wired in series, so each group of five produces 18 volts (5 x 3.6 volts = 18 volts). When cells or groups of cells are wired in parallel, the amp-hour (Ah) ratings are additive but the voltages are not, so connecting two 18-volt strings of 1.5-Ah cells in parallel produces an 18-volt 3.0-Ah battery pack. — David Frane