3/22/2014

Pergola Project

This past week my son came out from New Jersey for Spring Break for a visit. I fixed up a project for us to work on. Vicki and I had been planning pergola and this seemed like an ideal project to work on together. I bought a load of oak timbers for the project. I also opted for steel spikes as easier than digging 3 foot deep holes which is how I used to set fence posts on my farm in Oregon. I dislike the spikes as they have a steel box around the bottom of the post which I think detracts from their look. So I decided to set them in holes (6 inches deep) to hide the steel boxes. Since the spikes themselves are in the ground normally the risk of rust doesn't change. The choice of oak should mitigate rotting for 20 years or more. Here is what it looks like.


It was all built from green oak and Redington and I cut and fit all the joints. The joints are simple traditional joinery.

The first thing we had to do was make a template to cut the curved cross sections. We would use a router to create a the finished curve on each cross piece. This was to give a graceful look to the project but required some extra work. The template was cut from 1/2" plywood and the curve is based on a ellipse set by pressing in two thumbtacks and using a loop of string slightly longer than the distance between the two tacks. A pencil was placed in the loop and tensioned and a half ellipse was drawn on the wood.

Several attempts were made until the curve had the shallow grace I was looking for. I had to be careful to compensate for the offfsets caused by the router template guide and 1/2" bit that would make the final cut in the wood. Redington then next cut carefully to the line of the curve with a sabre-saw then sanded out any bumps or flat spots until we had a fair curve.

I screwed on a couple of cleats to position the template consistently against the oak plank. I also drilled two counter sunk holes. Short wood screws would serve to hold it tightly against the oak plank while we cut the plank.
The finished template with cleats in place.
Detail of cleat.
Next it was time to cut the first plank. We decided to prototype one complete pair of posts and cross piece to make sure the scale and height looked good in the garden.

The template was secured to the 1-1/4" x 8" x 6ft oak plank. Next the router was fitted with the template guide and a 1/2" straight cut bit 2" long. The depth was initially set on the router to just barely scribe the surface of the oak. The plan was to lightly route the path of the bit to mark it, then use the sabre-saw to cut away most of the waste and finish with a final pass with the router to give a clean edge. This would take longer but should reduce wear on the bit and make the cutting easier and less hazardous.

After the line was scribed with the router the template was removed and Redington used the sabre-saw to cut the waste away. Then the template was reattached using the same screw holes. The router depth was then set to 1/2" more than the thickness of the wood. This would leave the most worked end of the bit protruding below the plank and thus using the length of the bit that is rarely used. This produced a nice smooth curve. A simple decorative angle was cut on the end of the plank with the circular saw and it was finished.
Examples of the finished cross pieces.
Next the notches in the post tops where these cross pieces would rest had to be cut. The posts were 4x4 oak and would be cut to 90" to get the desired height. The circular saw and fence were used to cut the cheeks of the slots. Redington used an auger and 1" bit to drill out the end of the slot. Finally he used the sabre-saw to cut the bottom of the slot flat and finish the uncut areas the circular saw left.
Finished slots in the posts
Each set of these would be braced by a pair of 2x4s slotted in a similar manner though in the uncut faces. The finished joint looks as below...
The 2x4 resting in its slot and the crosspiece likewise behind it.
Next the spikes had to be carefully driven into the ground. First the 6 inch deep pockets were dug in the approximate position of each post. Much measurement and leveling was require to make sure they were accurately placed. Then Redington pounded them in using the sledge hammer and left over wood blocks. The vertical positions were checked and adjusted 3 times during the process.
Pounding in the spikes. 

The pockets keep the metal spike tops from being visible. 
Finally 3 small strips of oak were ripped and then screwed across the 2x4s to provide support for vines and other climbing plants.
The finished result.
Posing for a photo after completion. 

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