Outdoor Classroom

Drive stakes to locate the post hole centers. We used the side of the school building as a reference for measurements to make sure we remained square. Then, we measured from stake to stake for internal measurements. Here we see Lucas and Craig discussing taking a break after hours of work driving these six stakes. Not shown, cameraman Dave.

Here are the measurements between post holes from center to center.

59-1/2" between the two posts supporting each table section.

29-1/4" between the posts where the side tables meet the front table, with a 7-1/4" offset.

We made Craig dig all of the post holes by hand to a depth of about 30 inches.* Remember to call 811 or your region's equivalent utility locating service before doing any digging.

Your local codes may dictate a different depth depending on frost line or water level.

Pro tip: If you rent a post-hole auger from your local tool rental company, everyone else can take turns leaning on it while Craig digs.

Note: this picture shows two sets of holes for two tables. If you are making two tables, double the materials.

*Just kidding! Craig's arms aren't 30" long!

Measure and drive stakes to stretch string lines locating the posts. We located the strings at a corner of each post.

The posts are positioned properly when they are plumb in both directions and just kiss the stringlines. Use a 4' level to position them, attach kicker stakes to stabilize, and then back-fill each post hole with quick-drying cement mix.

In retrospect, Craig's technique of tweaking the post's plumb by head-banging (pictured) was ill-advised, and he wished that we had not kept advising him to do so.

The height of the post should be your final desired table height minus 1-1/2". Mark this measurement from the ground up on one post. Then, use a level to transfer the height from post to post.

Rather than freehand the cut, we used a crude saddle jig—two scraps screwed together at a right angle and clamped to the post—to guide the circ saw. If you do the same, be sure to offset your height measurement by the distance between the blade and baseplate edge of your saw.

We cut two kerfs then used those to finish the cut with a handsaw.

To prevent racking, we joined the cross beams to the posts with half-laps. We used a scrap 2x4 to mark the depth and thickness of the half-lap. Then, we used a circular saw set to 1-1/2" depth to cut kerfs for the half-laps. We completed the half-lap depth cut with a handsaw, working until its embarrassingly short-lived battery ran out.

Cut crossbeams from treated 2x4 lumber to 19". You'll need 13 per table. Clamp a crossbeam, centered, in the halflap of each post.

Construct the frame on the clamped cross beams. We started by centering 93" treated 2x4s on the ends of the front table cross beams and screwing them in place with 3" treated deck screws to create table aprons.

Next, we attached the 10' treated 2x4s to the outer edges of the side tables, flush with the front apron. The front aprons and the side cross beams should all line up as you attach the long side apron. Loosen the clamps and adjust the cross beams as necessary.

Attach 8' treated 2x4s for the inner aprons of the side tables. Add the remainder of the cross beams: Three centered between the posts, two used as nailers where the side tables meet the front table (see illustration, above), and two at the ends of the side tables (the outer aprons will probably run long and you'll have to cut it off flush).

Once the frame is assembled, level it in all directions by adjusting the clamped cross beams. Then, bore two holes through the crossbeams where they meet the halflaps, and lag-bolt the frame to the posts.

Finally, add twelve 8'-long 2x6s to serve as the table top, centering any overhang or spacing the boards to cover the frame as needed.

Remember to take off the little tags on the ends of the boards before you leave the jobsite, Craig.