While cutting smaller dimensional lumber such as 2x4s and 2x6s is a task that can be performed by a variety of different tools in one’s arsenal, cutting wide boards or commonly used thicker dimensional lumber, such as a 4×4, is more complicated.
While many power saws can make quick work of larger pieces of lumber, including chainsaws and reciprocating saws, these power tools generally won’t make precision cuts. Power saws designed for woodworking, including the circular saw, smaller miter saws, and the table saw, don’t provide enough cutting depth to get through a 4×4.
That might leave you wondering how to cut a deck post. The best way to cut a 4×4 post is by using a 12-inch miter saw, 10-inch radial arm saw, both of which can cut completely through a post in one pass, or a standard circular saw that can make precise cuts in two passes with the help of a simple jig.
This article will explore what tools can cut a 4×4 post and provide options for cutting through this larger dimensional lumber, even if it’s already mounted in the ground.
Contents (Jump to Topic)
What Is a 4×4 Post Commonly Used For?
The 4×4 post is a staple of outdoor woodworking. Its large diameter makes it structurally strong enough to serve as the vertical supports for decking and fencing. These posts are pressure treated to endure these outdoor applications and to allow for the post to be installed partially buried in the ground.
As with other dimensional lumber, a 4×4 post doesn’t meet its actual measurements and is instead a 1/2-inch shorter, making the actual size of the 4×4 post 3-1/2 inches by 3-1/2 inches.
How To Cut A 4×4 Post In 8 Easy Ways
The thickness of a 4×4 post makes it one of the more difficult pieces of dimensional lumber to cut cleanly for the power tools that most DIYers have in their shop. Most circular saws have a maximum cutting depth of 2-1/2 inches and, unless it’s a slide saw, a 10-inch miter saw can’t make a complete cut without some risky modifications to the tool’s safety features.
While a 4×4 post can easily be cut in twain by a chainsaw, it’s difficult, if not impossible, to do so with much precision. Such is also the case with a reciprocating saw. And, while cutting a 4×4 with an old-fashioned handsaw might offer more precision, it’s a laborious process that will slow down the project while wearing out your arm.
1. 12-Inch Miter Saw
The two additional inches afforded by the monster that is the 12-inch miter saw make cutting through 4x4s relatively easy. Unlike a 10-inch miter saw, a 12-inch miter saw will cut up to 4 inches deep, just enough depth to slice the blade cleanly through a 4×4 without the need to make risky changes to the saw’s safety features.
This method is ideal because it also offers precision. Once the 4×4 is positioned on the miter saw, line up the cut line with the blade and simply pull it through the wood. The size of the 12-inch blade makes it easier to cut through the wood than a 10-inch slide saw.
The most challenging aspect of cutting through the material is supporting the length of the 4×4 to make a level cut, a problem that can be solved by using a sturdy sawhorse.
The problem with a 12-inch miter saw is that most people don’t own them. These saws are considerably more expensive than a standard circular saw.
2. Radial Arm Saw or Slide Saw
There is less of a chance of one having a radial arm saw in their collection of power tools than a 12-inch miter saw. These large power tools are found mainly in pro woodshops. A radial arm saw consists of a circular saw attached to a long arm that allows the saw to move across a board perpendicularly.
This design allows it to cut wood up to a foot wide or more. In terms of depth, they aren’t any better or worse than a standard miter saw. Most radial arm saws have 10-inch blades, which allow for 3.5 inches of cutting depth.
The difference with a radial arm saw is that its sliding action allows it to make a complete cut, allowing it to overcome the curve of the blade to cut completely through a 4×4.
The slide saw, which is similar to a radial arm saw in that it can slide back and forth to cut wider boards, can cut through a 4×4 with a 10-inch blade.
3. Smaller Miter Saw
For those who don’t have the luxury of owning a 12-inch miter saw, it is possible to cut a 4×4 with a 10-inch miter saw. It’s just not possible with a single pass.
A 10-inch blade is tantalizingly close. It will cut to 3.5 inches deep, but the blade’s curve does not allow the blade to pass completely through the post.
Cutting a 4×4 with a miter saw that’s less than 12 inches requires you to make a cut, then rotate the board and make a second cut.
The setup is the same as with a 12-inch miter saw. Rest the post on the miter saw, using a sawhorse to support the off-end. Make the first cut, dropping the blade as deep as it will go before hitting the guard.
After that cut is complete, rotate the post 180 degrees so that the first cut is facing down on the miter saw. This step involves some skill, as aligning the two cuts can be crucial depending on what the post is being used for.
For a fence post or even a deck support post that’s going to rest on gravel and be supported by a cement base, an uneven end in which the cut is off by 1/8th of an inch won’t make much of a difference as that end will be buried in 2 or more feet of cement.
For more finished work, such as landscaping boxes made from 4×4 or furniture, a more precise cut is needed. To do this, use a stop block fence for the miter saw. Many miter saw stands come with this feature; however, they are expensive.
The stand extends the work surface of the miter saw, allowing it to hold a longer piece, such as a 4x4x8. This extended work surface features a lockable stop that serves as a place that the noncut end can rest against.
Simply push the 4×4 post against the block when cutting, flip, push it against the fence and make the second cut.
While a lock stop fence can be a valuable tool for cutting using a miter saw, it may be easier to forgo the miter saw together and instead pick up a circular saw.
4. Circular Saw
A circular saw is one of the best means of cutting a 4×4 post. Most people own a circular saw, its portability makes it easy to cut 4x4s from the ground, and they can make precision cuts by using a relatively simple trick.
Like miter saws that measure less than 12 inches, a circular saw’s 6.5-inch or 7.25-inch blade will not cut cleanly through a 4×4. The maximum depth of most circular saws is just 2.5 inches. This means you’ll need to make two cuts.
Having to make two cuts makes it easier to set up the cut. Because the blade cannot slice completely through the post, the cut can be made with the post resting on a paved driveway or the floor of a garage.
There are two ways to do this. The fastest method is by measuring and marking the cut line for the post on two opposing sides of the 2×4. Cut the first side, follow the cut line, rotate the board 180 degrees, and cut the second cut line completely through the post. While this method is effective, it likely won’t result in a precision cut.
For a more precise cut, create a simple jig by attaching three pieces of scrap plywood in a C-shape. One piece of plywood should be 3.5 inches wide, the same thickness as a 4×4. Attach two additional pieces of scrap plywood that are wider than 3.5 inches to the first piece, making sure that at least one side of the piece is perfectly flush.
This C-shaped jig should be able to cradle a 4×4. To use the jig, measure and draw a cut line on the 4×4. Next, measure a second line from the cut line that accounts for the width between the blade and the edge of the circular saw’s fence.
Attach the jig, lining up its edge with the second line. Then clamp the jig tightly to the 4×4.
Cut with the circular saw, using the fence as a guide. Then flip and make the second cut. The jig keeps the circular saw blade in line, resulting in a precision cut.
5. Reciprocating Saw
With its long blade, a reciprocating saw has little trouble cutting through a fence post. Most reciprocating saw blades range from 3 to 12 inches, meaning they have plenty of length to handle the 3.5-inch thickness of a 4×4 post.
The design of a reciprocating saw also makes them ideal for cutting through fence posts that are already in the ground.
The drawback of using a reciprocating saw is that it is a tool designed for rough cuts and demolition. This tool is not designed to make precision cuts. This limits its usability for cutting posts.
One option for making reciprocating saws more precise is by constructing a jig. Construct the jig using the same c-shaped design for a circular saw detailed above. However, unlike a circular saw, the fence will provide a guide for the blade as opposed to its guard.
To prevent the saw from cutting into the guard, attach metal flashing around the entire lip of the jig.
Make a cutline on the post, attach the guard to the post using screws, and line up the guard with the cut line. Cut with the reciprocating saw, keeping the blade flush against the metal flashing of the jig.
Though not as precise as a circular saw, this metal guide will allow for a more even cut with a reciprocating saw while preventing the blade from cutting the jig.
6. Table Saw
A 10-inch table saw can cut with a maximum depth of 3.5 inches, making it just large enough to cut completely through a 4×4. That said, a table saw, by design, is awkward for cross-cutting a 4×4 post that is 8 feet long even with the help of a fence.
A long 4×4 piece of lumber is difficult to move evenly through the table saw’s blade even with another pair of hands to help guide the lumber. This makes it difficult to keep the end of the post against the table saw’s fence to execute and even cut.
Table saws do offer the unique ability to rip-cut a fence post, which is not something that can be performed by any other power tool.
7. Chainsaw
A 4×4 post is similar in diameter and shape to a small tree. As such, a chainsaw is well suited for cutting through a post. That said, chainsaws are not designed to make precision cuts, limiting how useful they are for cutting posts used for fencing, a deck, or any other purpose.
There are options for making a chain saw more precise for cutting posts that are already in the ground. One method involves creating a 2×4 fence. Use four lengths of 2x4s to create a box shape around the 4×4 so that the top edge of each of the four 2×4 lengths are flush against the cut line.
This fence will serve as a guide for the chainsaw blade. Let the weight of the chainsaw bar rest flat on the guard as you cut across the post. This will keep the chainsaw level as you cut, resulting in a much more precise cut than using the chainsaw freehand.
8. Hand Saw
Using a handsaw is perhaps the least ideal means of cutting a 4×4 post, largely because it requires arm power versus the power of an electric motor or gas engine. But, because a handsaw is a slower process, it can be a more accurate way to cut a 4×4.
When using a hand saw, begin by drawing a cut line on the post’s top and front side. This will serve as a guide that will allow you to monitor the progress of the cut and ensure it stays on a straight line.
Begin by making a back cut with the saw on the line to create a groove that the blade can slide through. Once you’ve established the groove, begin making back and forth cuts with the saw.
Make long strokes that use as much of the blade length as possible. This will make for a smoother cut and help keep the blade in line with the cut line. Stop periodically to make sure the blade is in line with the cut and make adjustments as needed.
Can a Jigsaw Cut a 4×4?
You might think the answer to this question would be no. Most jigsaw blades can cut to a maximum depth of 1-1/2 inches, which is well below the depth needed for cutting through a 4×4.
And, since a jigsaw blade is perpendicular to the saw’s guard and cuts using an up and down motion, it cannot cut through material thicker than the blade like a circular saw or miter saw can.
That said, there are specialty jigsaw blades that are as much as 5-1/4 inches long, which is more than enough to cut through the thickness of 3-1/2 inches.
But, before hunting down one of these blades, keep in mind that many jigsaws do not have the raw power to cut through material that thick.
This can make cutting through a 4×4 with a jigsaw blade a long process that can wear on the saw’s motor.
Jigsaw blades are also thinner than circular saw blades, which means they bend more easily. The longer the blade, the more likely it is to bend to the left or right as it moves through the wood. That means getting an even cut on a 4×4 using a jigsaw is very difficult.
For these reasons, using a jigsaw to cut through a 4×4 is best employed as a last resort.
How to Cut a 4×4 at an Angle
You have a couple of options when it comes to cutting a 4×4 at an angle. Let’s start with the hard option. A miter box used in conjunction with a handsaw will allow you to make a fairly precise cut.
Simply place the 4×4 in the miter box and use the desired pre-cut angled fence to cut. While this cut doesn’t require much skill, it is the most time-consuming and laborious option, especially if you need to cut multiple 4x4s at an angle.
The easier option is to use a miter saw, which is built for making angled cuts. Unlike a miter box, a miter saw allows for a virtually unlimited number of angle options between 90 degrees and its max angle, which is typically between 45 and 50 degrees. Of course, to make an angle cut on a 4×4 with a miter saw, you must have a 12-inch miter saw.
With a little help from a jig, you can also make angle cuts to posts that are already in the ground with a reciprocating saw. Jigs, such as this model for reciprocating saws, create the angle which provides a fence for the blade as it moves through the 4×4.
How to Notch a 4×4 Deck Post
The easiest way to notch a deck post is with a circular saw. First, take measurements of the length and width of the girder that the post will hold to get the right measurements for the notch. Use those measurements to draw cut lines on either side of the post for the notch.
The method for cutting is to use a circular saw to cut along each cut line. Keep in mind that the circular shape of the saw blade will not allow you to complete the cut.
Do not cut beyond the cut line to complete the cut. This will weaken the post, which could cause it to split or crack when the weight of the girder and deck are applied to it.
Instead, use a reciprocating saw or hand saw to complete the cut, making sure not to cut past the cut line. If the notch won’t pop out after cutting, use a chisel and hammer to knock the notch out.
Wedge the chisel into the cut end of the post and use a hammer to knock the notch out. Once the notch is out, use a chisel to clean up the notch, so the girder sits flush when installed.
Conclusion – What Is the Best Way to Cut a 4×4?
While the best way to cut through a 4×4 is by using a 12-inch miter saw or a 10-inch radial saw or slide saw, those tools aren’t always readily available. With a little ingenuity, it’s possible to make precision cuts with other tools, including circular saws, reciprocating saws, chainsaws, and even handsaws.
Whatever tool you decide to use, make sure to follow safety protocols. Avoid the temptation to remove safety features to increase the depth a saw can cut. It’s not worth the risk and may damage the tool’s motor, as it is not designed to cut to depths that go beyond its safety guards.