Overview: Benefits and tools
Honing your circular saw skills will pay big dividends when you're building decks and fences. Good techniques will speed up your work, create stronger joints and show off your craft, since all the cuts and joints are highly visible. In this story, we'll show you how to get a perfectly square cut on the end of a 6x6 post, cut notches and shape deck posts with your circular saw.
You'll need a circular saw with a sharp 7-1/4-in. blade to make the deep cuts we'll be showing. A 24-tooth carbide blade (at hardware stores and home centers) is a good deck-building blade.
Square Your Saw Blade
You can't make clean cuts unless the blade is square to the saw's bed. Most saws have an adjustment screw near the angle gauge for this purpose. With the saw unplugged and the blade set to maximum depth, retract the blade guard and hold a square against the bed and blade to make sure they're exactly 90 degrees to each other. Adjust the screw if necessary.
Next check to make sure the blade is parallel to the saw bed. With the saw unplugged and blade fully extended, hook a combination square or Speed square on the back of the bed and slide it tight to the blade. They should line up. Most saws don't have adjusting screws for this. Make adjustments by carefully bending the bed sideways until the blade and bed are parallel.
Technique 1: Square-cut a 6x6 post
Photo 1: Saw around the post
Mark the post for length and use a Speed square or combination square to draw a line around the post. Make sure all the lines meet at the corners. Set the saw for maximum depth and saw to the waste side of the first line. Rotate the post 90 degrees and using the first cut as a guide, cut the second side. Cut the third and fourth sides the same way.
Here's an easy method for making a smooth, clean cut on a 6x6 when you cut it to length. By rotating the post a quarter turn after each cut, you can use the previous cut to guide the blade for the next cut. Since a 7-1/4-in. blade cuts a little less than halfway through, you'll have to finish the cut with a handsaw. To prevent kickback, position both sawhorses on the keeper side of the line and allow the cutoff piece to fall.
Technique 2: Notch a 6x6 post to support beams
Create a sturdy connection by notching a 6x6 post to accept a beam. You could make these notches using the technique shown in Technique 3 below, but the ripping method shown here is a little faster, especially for long notches. If you're using treated posts, brush a wood preservative onto the freshly exposed wood.
Technique 3: Notch the middle of a post
Rail posts often require notching to fit around a deck joist (Photos 2 and 3). Enclosed notches like these are easy to make with a series of saw kerfs. After the chunks are broken out, you'll have a little cleanup to do with a sharp wood chisel.
Technique 4: Cut a decorative post top
Photo 1: Cut angles with a guide collar
Screw lengths of 1x6 together as shown to make a tight-fitting collar for your post. Rough-cut your post about 4 in. longer than its finished length. Screw the collar to the post about 7 in. from the end. Set the saw to cut a 45-degree angle and adjust the blade to cut about 1-1/2 in. deep. Keep the saw bed tight to the collar as you saw all four sides of the post.
Photos 1 - 3 show one way to cut a decorative post top using a simple wood collar as a guide for the saw. Make the collar by cutting two pieces of 1x6 about 1/32 in. longer than the post width and two more pieces 1-1/2 in. longer than this. Screw the pieces together to form a snug-fitting collar. Slide the collar over the 4x4 and secure it with two screws on opposite sides to hold it in place. The holes left from the screws will swell shut and become nearly invisible with time. Practice various patterns on a scrap 4x4 and keep track of all the collar locations by marking the post before you reposition the collar. When you have a design you like, simply transfer these marks to each post to duplicate the cuts.
In Photo 1, we show cutting the 45-degree angles on the post top before cutting the post to length. The extra post length supports the bed of the saw, making it easier to cut accurate angles.
You can cut any size groove with a circular saw if you're patient enough to make multiple passes (Photo 3). But you'll save time and get better results using the same collar to guide a router fitted with a straight-cutting router bit.