Do you take the time to check the accuracy of your circular saw? you know you should
Whether you want to make straight cuts by guiding your circular saw over a rafter square or ruler, or follow a line freehand, even the best circular saw needs adjustment for precise cuts. This means calibrating your cut line markers and making sure the shoe is parallel to the blade.
Check 90 degree circular saw accuracy
The circular saw has two cut line marking notches, one for square cuts and the other for 45° bevel cuts. To check them for accuracy, start with a square marker. Almost every saw we've tested has an adjustable set screw for this calibration. Make sure the saw blade is at exactly 90° to the shoe and cuts a few inches of wood. Hold the saw against a square or ruler. Stop the blade and remove the saw from the cut while keeping it against the edge guide.
See if the kerf made by the blade lines up with the mark. If not, use a permanent marker or scoring cone to carefully transfer the actual cut location and width to the saw shoe. You can also draw on white tape to see the lines better. It helps if the equipment you use to guide the saw is clamped to the wood for this marking operation.
If the cut is aligned with the marked side but thinner than the notch, mark the missing side below the notch. For a really precise cut, you want to be able to cut consistently and precisely to either side of the mark.
Check 45 degree circular saw accuracy
After making sure the saw blade is set at 45°, repeat this process for the miter cut line marks. Cutting a flat piece of wood and measuring the resulting angle is usually more accurate than measuring the angle between the shoe and blade. Any deviation from the flatness of the shoe – which is unfortunately not uncommon – will affect your measurements.
Check that the blades are parallel
It is important to check that the blade is parallel to the shoe. It ensures true cuts whenever you rely on guiding your saw along a square or ruler. Like a ship's rudder, the saw will follow the direction the blade is pointing. If the blade deviates from the edge, the saw will dig into the material. If the blade leans towards the edge, the blade will bend and bind, stopping all forward progress. Elevating the blade so that the teeth just clear the cut radically increases the flexibility of the blade. However, the more the blade is in the cut, the more it will help keep the cut straight and square.
When in doubt, read the manual
To repair a saw with a misaligned baseplate, check the manual or the brand's technical service department for advice. You can verify this misalignment by measuring the distance from the edge of the shoe to the farthest forward and rearward point of the blade.
My trusty old cord saw can adjust for blade parallelism, but I've rarely seen anything like it on cordless saws. If bolts attach the saw body to the track shoes, you may need to loosen all bolts and then retighten them with the saw twisted in the desired direction. Failing that, you may need to carefully bend or pry some of the linkage parts that hold the body and shoe together. You can even twist the body and shoes apart. If it's not an easy fix and the saw is new, take it back. If it's not returnable, take the necessary steps to fix it. For maximum cutting precision, you need a saw that cuts straight and accurately.