How to Set and Cut Deck Posts Like a Pro

The day before you set the posts, make sure their ends are square. Mark the cut lines with a speed square and make the cuts with a miter saw or circular saw. Dip the cut ends in wood preservative and let them sit overnight.

Set each deck post in its anchor. While someone holds it plumb, drive one nail through the anchor hole and about halfway into the post. This will keep the bottom in place but allow you to move it when you plumb it. Tack 1x4 bracing to the post and stake in position.

When you've set and temporarily braced all the deck posts, restring the mason's lines on the marks that represent the outside edge of the posts. Clamp a second 1x4 brace to the post and stake it. Plumb each deck post with a post level, keeping its outside face against the mason's line.

Recheck the post alignment by sighting down the mason's line. Replumb any post that looks out of line and adjust the bottom of the post if necessary. If you have a post that's plumb but slightly bowed (no more than 1/8 inch), you can force it into place when you install the beams or joists.

Drive the remaining fasteners into the post anchor. Some anchors are made to accept nails or screws only. Others are fabricated to accept a lag screw also. Predrill for the lag screw before driving it.

Use a water level to establish the height of each post. Fasten one end of the water level so the water line is even with the bottom of the ledger (or level with whatever edge your plan prescribes). Hold the water level on each post and mark the post at the water line. Transfer the mark around the posts.

You can mark the cut line for the posts by using the depth of the joist and/or beam, depending on your construction plan. Starting at the line that is level with the bottom of the ledger, measure down the depth of the joist and mark this point.

Transfer the cut line to all the faces of the deck posts, using a speed square and a carpenter's pencil. Make this line dark enough so you can see it when the sawdust flies. You will need to be able to see the line to keep the blade from wandering.

Holding the weight of a circular saw at right angles to the post can prove cumbersome (and even dangerous), especially when standing on a ladder for a raised deck. A reciprocating saw will prove more accurate. Keep the shoe of the saw on the surface of the post and make sure the blade cuts straight along the line.