Monday, March 15, 2010

Three Kinds of Circular Saws for Three Different Jobs

          While there are many types and sizes of circular saws on the market, I would like to discuss what I believe to be the three most important categories. They are: plunge saws with guide rails, worm drive or hypoid saws for construction use and standard-drive circular saws suitable for both home and construction use. Before I delve into all of that, however, I’d like to take a quick look at the basics.



          A circular saw allows you to take a relatively small tool to a large work piece and cut it without too much back-breaking labor. In the past, the price for this convenience was inaccuracy because there was no really easy way to force a circular saw to cut straight along a pencil line. For rough construction work like roofing and decking, this was no problem. For fine woodworking, however, the circular saw was not the tool of choice. Most woodworkers rely on the table saw to get the long, straight cuts they need and for good reason. The fence on a table saw gives the constant reference point needed for straight cuts.


          Sometimes, however, using a table saw to trim the top of a huge conference table, for instance, turns out to be an impossible task, especially when trying to trim off the ends at 90 degrees to the sides. That’s when a very carefully planned approach using a circular saw seems to deliver the best final result. I would draw a pencil line using a long straightedge exactly where I wanted the trim cut to go. I would then carefully measure the distance between the inside (or outside) of the saw blade and the edge of the foot plate of the saw. The next step would be a second pencil line, parallel to the first one and separated from it by the distance I measured between the inside (or outside) of the saw blade and the edge of the foot plate. I would locate an absolutely straight board (ripped straight on the table saw, if necessary) and clamp this across the table top as a guide along the second pencil line. Then, I could make a pretty straight cut along the first pencil line. I would then repeat this for the other end of the table top.


          In the past few years, this process has become a whole lot easier. There are now several makes and models of plunge saws that run along metal guide rails, cutting right next to the edge of the rail without cutting into the rail itself. The guide rails don’t even need to be clamped to the surface being cut because they have material underneath that keeps them from sliding around. If you feel more comfortable clamping down the guide rail, this can be done, as well. It’s a simple matter to lay the guide with its edge along the cut line and then to take the saw and run it down the rail, cutting right next to the lip of the rail.


          Because these saws are plunge-type saws, you can begin and/or end a cut in the middle of a sheet of plywood. You could cut out a window or door opening, for instance and have it come out clean and square every time. The best thing about using these track saws is the confidence they give you: You KNOW you can do a perfect job, quickly, accurately, over and over again.


          Another kind of circular saw I’ve used a lot over the years, mostly for construction, is the worm drive saw pioneered by Skil. A framing carpenter needs to be able to cut a lot of lumber all day long. While accuracy is always desirable, it is not as critical to the framer as it would be to a finish carpenter or cabinet maker. Speed is the thing that the framer wants on his side and he (or she) does not want to be saddled with a saw that can’t cut the mustard, so to speak. He doesn’t want his circular saw to bog down in the middle of cutting a 2 x10 joist or have the sole plate hang up every time it goes across the edge of another board. He does not want to have the saw blade slipping around the saw arbor. What he wants is clean, fast accurate cuts: In short, power.


          A worm drive saw delivers the constant power he needs because there is no slack or play anywhere between the powerful motor and the saw teeth that are doing the cutting. The worm gear cuts down a bit on saw blade RPM but trades this off for torque. It is torque, more than speed, that powers a saw blade through thick, wet wood. A diamond-shaped arbor makes it virtually impossible for the blade with a matching diamond-shaped hole to rotate around the arbor. Keeping the number of saw teeth down to 18-24 teeth on a 7 1/4" saw blade also helps. The only problem with early Skil worm drive saws was the weight with those large motors and all that gearing. The solution was to use magnesium instead steel in the construction of the saw wherever possible. The modern magnesium worm drive saws weigh only about 14 to 15 pounds which is more than a standard circular saw but manageable in the strong hands of a muscular framer.


          The final category included the kind of saw that most people think of as a circular saw. It is lighter than the worm drive saws and, for most uses, it's plenty powerful enough. Some of these saws are now also be made out of magnesium parts and weigh just over 10 Lbs. This makes them easy to use by the average do-it-yourselfer. Did I mention that they are a lot less expensive than the other types?



Bob Gillespie
Woodworker

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© 2010 Robert M. Gillespie, Jr.

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