Our house has a large deck out back, and ever since we moved in, Holly and I had been looking at what kind of deck furniture we could get for the deck so that we could eat outside and have others over and eat outside. We looked at patio furniture, but it was more expensive than what we wanted to pay. As I was starting to think that maybe we could make a picnic table, my brother-in-law and sister built a picnic table for their house. Their picnic table turned out nice and was not expensive, so I determined that I would try to make a picnic table myself.
We were busy enough last summer with house stuff and getting ready for Claire that I didn't want to undertake the project last year, but this spring, I definitely wanted to get something done so we could enjoy eating outside throughout the summer. I worked on putting together some plans based on the design that Sarah and Kevin had used and another site that I found on the internet. I made some changes to the designs based on comments from Sarah and Kevin and adjusted the height of the table top and the bench to get them to match our dining table since that is comfortable for us.
The final design that I came up with is for a 7 ft. long table with a table-top width of approximately 41 in. The table-top height was designed to be 30 1/2 in., and the seat height was designed to be 18 in. I included two diagonal cross-braces to stiffen the table against wobbling length-wise. My original design was sketched out on quad-ruled paper, but for this post, I drew it up in AutoCAD to make it more clear and legible. You can download a PDF of the picnic table design. The drawing includes a couple of views of the table, a list of pieces, and a parts list for a trip to the hardware store. (If you want the CAD file to modify for yourself, feel free to contact me.)
You can see the other web pages referenced above for some ideas for how to assemble the table. What I did is first attach the table top supports to the center board of the table top, taking care to get everything square. Then I attached the other table top boards to the table top supports. The carriage bolts ended up being the perfect width to put temporarily between the boards to space out the table top boards.
With the top assembled, I flipped the top over and attached the table legs. I used clamps to hold the legs in place while I drilled the bolt-holes and installed the carriage bolts. I had some difficulty getting the ends of the legs to stay flush with the bottom of the table top, and this led to the table sitting about an inch lower than designed. It was also difficult to install the nuts on the carriage bolts because the locknuts that I used took more torque to turn on than what the bolt would resist when pounded in, so I ended up having to hold the bolt with vicegrips to keep it from turning. It might have worked better to use a non-locking nut with a lock washer instead so the bolt would be tightened down pretty well before the nut started taking more torque to turn.
After installing the legs, I measured and marked the distance from the bottom of the table top to where the seat supports needed to attach to the legs. I needed help to hold the seat supports centered and level to get them clamped down for drilling the bolt holes and installing the bolts.
With the seat supports in place, the last pieces to install with the table still upside-down were the diagonal braces. These are probably the most precision-fit pieces in the whole table, and surprisingly, they actually fit right in. I guess trigonometry is good for something after all.
Then the table was flipped over to right-side up. It is actually pretty heavy and was not easy for Holly and I to flip it; we probably could have used a third person to help lift and rotate the table. The final items to install were the bench seats. I started with the outside 2x4s and then spaced the other boards inward from there. For spacing between the boards, I used decking screws rather than carriage bolts to get a smaller spacing between the boards.
When the table was all assembled, Kevin took his belt sander to the table to smooth out the corners and reduce the splinters on the wood. We didn't get all of the screws on the table top down quite far enough, so the sander took the coating off the top of some of the screws. With exposure to the weather, these screws may end up needing to be replaced if they show signs of significant corrosion.