Tool basics – cordless circular saws

When the first cordless tools appeared in the 1980s, they were all limited by the same thing: wimpy batteries. That's why it's been interesting to watch new tools emerge in cordless form because batteries and chargers have improved. With each incremental rise in battery power and longevity, technical possibilities become realities. And of these, I find the development of cordless circular saws the most startling.

It's now possible to frame an entire house efficiently using only the cutting power of a cordless saw and a pair of batteries swapped back and forth in the charger. Cordless saws still aren't quite as gutsy as corded models, but manufacturers tell me that their largest cordless saws are designed to provide 80 per cent of the output of corded models. And that's enough to handle the full range of cutting jobs without excuses. Even 45° bevels are possible with the large-blade models. The question isn't whether these saws are able to cut serious lumber, but whether cordless suits your style of work. Is cord-free cutting worth a higher purchase price, plus the occasional and not-so-insignificant expense of replacing batteries?

Many of these saws are available as kits with other cordless tools, often drills. If you need the extras, these kits can be a better buy than the saw alone.

Before running a range of cordless saws through their paces on construction lumber (with about 20 per cent moisture content), I took a close look at each model in my workshop. After operating guards and triggers, installing blades and charging batteries, each saw was used to rip and crosscut 2 x 8 stock to assess their stamina, ease of use, control layout and general field performance. The results boosted my confidence in this tool category more than I thought possible.

Big on Blades

One reason early cordless saws couldn't handle all cutting tasks was because of their small-diameter blades-some only 4 3/8" across. But as power increased, larger blades became possible. You'll now find 6 1/2" blades on most 18-volt cordless saws, and 7 1/4" blades on some 24-volt machines. To maximize cutting power, cordless saws use thin-kerf blades with low-friction coatings. These work just as well as full-thickness blades in my experience.

When choosing a cordless saw, consider depth of cut and how it relates to blade size. The smallest machines currently spin 5 1/2" blades, which is just barely enough to square-cut standard 2-by framing lumber. Consider models with a 6 1/2" or 7 1/4" blade if you're planning to cut thicker rough lumber, or regular framing stock at bevelled angles.

 

 

Battery basics

After blade size, think about batteries as you walk down the tool store aisle. Voltage is a rough guide to power, cutting depth and speed, but there are trade-offs to high voltage-including tool cost, weight and the price of replacement battery packs. That said, I've found you're going to need at least an 18-volt machine if you want to work without a corded saw standing by. Lower-voltage cordless saws are fine as supplemental tools, but most users demand greater output for some tasks than these can provide. In the timed trials I ran, 24-volt saws could rip the length of a 10' 2 x 8 in about 35 seconds. Eighteen-volt machines did the work in slightly more than one minute. A 14.4-volt saw typically took 80 seconds to accomplish the same thing.

Battery weight is another significant issue. The heaviest 24-volt battery, for instance, tips the scale at more than 3.25 lbs. Compare that with an 18-volt battery at about 2.5 lbs. That's why there's more than just cost involved when considering saw voltage and performance. How strong is your arm?

Inside a typical cordless tool battery pack you'll find cylindrical cells connected together in series. The most popular cell size in cordless tool battery packs is called Sub-C-slightly smaller than over-the-counter C-sized batteries. Research efforts have been focused on Sub-C, making it the most cost-effective and popular choice for cordless tool manufacturers.

But why don't they last forever? With higher electrical drain rates becoming more common, battery problems are often heat-related. Rapid discharge-common in cordless saws- generates heat that can cause insulating layers in a cell to deteriorate, leading to an internal short-circuit condition. This means even more internal heat is generated as surrounding areas of the cell must discharge more quickly to make up for the energy shortfall. Battery packs sometimes last longer than four years of daily professional use, but most fail after two to three years because of heat-induced breakdown of internal cell insulation.

By a strange coincidence of technology, cordless tool development has been spurred by similar research for another class of high-drain battery users: remote-control toys.

By avoiding anything that boosts tool load and current draw beyond what's necessary, you'll optimize battery life. Keep saw blades sharp and avoid prolonged stall conditions. Battery life drops off quickly when motors strain and stop under load, with momentary current draw high enough to deliver the same energy output as a stovetop cooking element at full power.

 

 

Little things that matter

It used to be that most corded circular saws had blades on the right-hand side of the tool-ideal for southpaws but not so good for everyone else. Worm-drive saws were the exception to this rule for some reason, and most cordless saws have followed the left-hand blade lead. It makes it easier for right-handers to see the cutting line and follow it more closely. Right-side-blade saws are available for left-handers too.

The fit, finish and function of tool controls and guards strongly influences how a tool feels in the hand. Robust, solid controls that promise to withstand years of field duty do a lot to inspire confidence in any tool. And next to the on/off switch, the retractable blade guard is the most commonly handled feature of any circular saw. I like all-metal guards because they're solid and are likely to withstand real-world abuse. Perhaps this is personal preference, but plastic blade guards often don't inspire the same level of confidence. Many plastic guards flex or wiggle more than metal ones, and I find that distracting.

Another thing to watch for while you're saw-shopping is safety-switch location. All cordless saws include an interlock button that must be pushed down before the on/off trigger can move. My favourite style is the thumb-operated, top-mounted safety button. I find it easier to use and less tiring on the hand than the side-to-side slide switch that's more common in this group. Try the different types in the store before making a buying decision.

Finally...

Cordless saw choice is more varied than it was when the tool category first emerged in the mid-1990s. As manufacturers pour money into tool development, some brands forge ahead with higher-voltage electrics, larger blades and greater capabilities, while others lag behind, resting on yesterday's technological laurels. The performance gap between different makes and models of cordless saws is widening. If you're planning to do renovations and new construction using only a cordless saw, then look at models with 18-volt power or higher. You'll also need a second battery to keep the tool working non-stop. If your cordless saw will only supplement corded cutting, then a 14.4-volt machine will keep you happy, with lighter weight, a lower purchase price and less expensive replacement batteries.

External brush ports are a newer, welcome addition to many cordless tools, allowing you to inspect and replace carbon motor brushes easily and extend the tool's working life

Accurate depth-of-cut control-safer, faster and more precise than measuring or eyeballing the blade depth-puts cordless saws in the big leagues.


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