An angle grinder probably isn't the first cordless tool you'll buy, but one of the current models can make a useful addition to a tradesman's off-the-grid arsenal. Like 18-volt recip saws and rotary hammers, these grinders won't come close to replacing a corded version for all-day use, but most of them proved capable enough to have around for average jobs or for whenever the ease and convenience of cordless grinding and cutting is preferred.
As a way to lower users' expectations of how much work they could get out of these typically underpowered tools, some manufacturers used to refer to their cordless tools as cut-off tools, instead of grinders. But better motors and batteries have made the latest models good enough to be called grinders by every brand. A few are still best suited for light-duty work, but to my surprise, most of these tools are real go-getters, capable of making the sparks fly during rigorous grinding work … for a short while at least.
I chose the kit form of the grinders (with batteries, charger, and case) where I had the option. All are available a la carte as add-on tools, but some are sold only that way.
To determine each tool's mettle on metal, I made countless cuts and ground away lots of steel. I chose grade 40, #4 rebar for the competitive trials. Besides being a familiar material to builders and remodelers, rebar is made very uniformly to government specs. Its carbon steel is tougher than mild steels used in general fabrication work.
To keep things even, I used identical 4 1/2-inch cut-off and grinding wheels from Norton in all of the grinders, even though some of the tools will fit 5-inch wheels.
The tools also spent time in a professional welding and fabrication shop in the skilled hands of grinding maestros; craftsmen who wield an angle grinder with the ease and grace of a conductor's baton. These guys gave me great feedback regarding the finesse and ergonomics of these grinders. When fabricators need to remove a lot of metal in the shop, they typically grab a larger grinder, but smaller models like the ones in the test spend much of the day in their hands, blending and finishing surfaces before and after each weld they make.
The average building contractor may not spend the day with an angle grinder in hand, but for many uses, they are arguably the best tool for the job. Besides the obvious metal cutting and grinding uses, there are other tasks for which a grinder could be your go-to tool.
Any time you have to cut or smooth metal against concrete or masonry, a disposable abrasive wheel has a real edge over toothed cutting blades that can easily be dulled or damaged. Cutting off misplaced rebar or anchor bolts flush to a foundation wall or grinding the stubs of concrete-form ties are good jobs for small grinders on site. For masonry itself, smoothing ridges left on concrete walls from form seams, demoing tile walls—backerboard and all—or slicing through plaster or stucco without ripping out the expanded metal lath are all great uses. In addition, during remodeling jobs, a grinder fitted with a thin cut-off wheel may be the smoothest way to cut neatly through mudded-in corner bead without tearing it from the drywall.
At minimum, each grinder comes with a side handle, adjustable guard, and wheel attachment wrench, but some of the tools include a few extra accessories. Every brand has a switch circuit that protects the user against accidental startup. If you put the battery in with the switch turned on, the tool won't run until the switch is turned off first, then turned back on.
Despite the relative simplicity of angle grinders, there are beneficial features that stood out during the testing:
- Grinder guards that do not require tools to attach or reposition are the key to efficient guard-adjusting.
- Each tool comes with an open-bottom (Type 27) grinder guard, but models that also include an enclosed-bottom (Type 1) cut-off-wheel guard add to their utility and safety while cutting.
- All of the tools have spindle lock buttons that let you tighten wheels with just one wrench, and a few of the tools have tool-free options for removing and even attaching wheels.
- Grinders with lock-on switches allow more freedom of movement and create less fatigue than those with a paddle switch or trigger that must be held on.
- The grinders that fit 5-inch wheels allow you to use longer-lasting cut-off wheels, however, the extra torque required for grinding with a larger wheel may sap the tool's strength.
- Grinders with motor brakes increase productivity because you can set the tool down immediately after use, instead of waiting for the wheel to stop.
- While it was hard to detect the exact benefit in use, two of the top models feature high-tech brushless motors with electronic instead of brushed commutation designed for high-efficiency operation.
Battery: 18 volts, 4.0 Ah
Comments: Solid third-place tool with great runtime and a light, agile form, but it slows under load more than the top two.
Battery: 18 volts, 4.0 Ah
Comments: A strong tool that gets extra torque from its slower motor, but its bulky rear handle with a trigger is not preferred over a standard grinder design.
Hitachi G18DSL P4
Battery: 18 volts, 3.0 Ah
Comments: Light-duty tool with only modest power and runtime; outclassed by other tools in the test but its compact form was appreciated for lighter finishing work.
Battery: 18 volts, 5.2 Ah
Comments: Firsts in every test really says it all; hands-down the best tool for serious cutting and grinding with powerful and predictable performance.
Milwaukee Fuel M18 Brushless
Battery: 18 volts, 4.0 Ah
Comments: Strong, smooth second-place tool. A real comfort standout. Comes with useful accessories and extras.
Battery: 18 volts, 4.0 Ah
Comments: Light-duty tool that stalls quickly and frequently under load due to its overprotective battery feedback circuit. This characteristic makes it frustrating to use and limits the tool to timid grinding and cutting uses only.
The Bottom Line
Once the flying sparks had bounced their last, the grinding swarf had all settled, and the hot steel had cooled, I had to admit that I was quite impressed by the performance of these 18-volt cordless angle grinders. Of course, like many cordless tools, the minutes of actual runtime under a decent load can be counted on one hand, but when you consider that equals about 45 cuts through #4 rebar, it's a respectable amount of work. All of the tools could do the light grinding of finishing work such as smoothing welds and putting a radius on sharp corners, but when pushed harder, the more powerful tools proved their worth for serious grinding and cutting.
The Metabo takes the top spot, as it won every single power, speed, and runtime test. It also has advanced features. In the No. 2 spot is the Milwaukee, with a great combination of power when it counts the most and many advanced features. Great performances by Bosch and Hilti have them sharing third, and the powerful yet clumsy DeWalt follows. The light-duty Hitachi was a comfort standout, especially for finish work, but is really not in the same class as the more powerful tools above. The Ridgid trailed behind all with its timid output, doomed by a load limiter set too far below the level of work a cordless grinder needs to do.
During testing, materials to be cut and ground were secured in a vise and supported along their length to minimize vibration. Identical new 4 1/2 inch cutting or grinding wheels were installed on each tool prior to each test.
Number of cuts through 1/2-inch rebar on a fully charged battery. Tested with Norton RightCut Type 1 cut-off wheels, .040-inch thick.
Grams of steel removed per minute during two, 2-minute trials of heavy grinding on a fully charged battery. Tested on rebar with Norton Gemini Type 27 grinding wheels. A corded model was included as a point of reference.
Time in seconds to make 10 cuts non-stop through 1/2-inch rebar on a fully charged battery. Tested with Norton RightCut Type 1 cut-off wheels, .040-inch thick.