I'm extending an existing wooden fence - a typical cedar fence with the up/down curvature (conture). I was going pre cut the pickets using the existing pickets as a template (match the curve/size of each). But then I realized some fence sections had 8-10 pickets on each (fence sections were not exactly equal) - meaning precutting really would not work since I'm not sure how many pickets exactly my new fence will take.

In any case, what is the easiest way of matching the conture of the existing fence? How do the pros do this, I'm sure it's easy but can't figure a real good way to do this.

My plan is simply to install the fence with full length pickets, then go back and cut the right conture with a recip or cir saw, but mapping that correct curve is the trick - thanks in advance for your advice.

 

do a search , Im prety sure its been covred here before . once not to long ago

 

go to home depot and buy a length of mdf window casing or baseboard-(the stuff that is primed white)-you can drill a hole on each end -tie a string from hole to hole and make a bow to use as a pattern for the contour you want.

 

OK first my painful way and then his way...

Working alone, I built my own 20' fence with positive arch.
I wanted to make a template to use to draw the arch on the fence. I tried to get string to work hanging upside down on fiberboard to create a but I could never get it to hang neatly and symmetrically. I also bought a strip of steel that bent, but it too was not symmetric because it tended to overbend in places. Finally, I used the steel to get one good half-arch and cut the half-arch using 1/4 inch fiberboard. I then clamped a level along the fence panel and then drew half the arc using the template, flipping it over to create the other side. Balanced and precise but time consuming. I cut it with a jigsaw, which was probably too fine and difficult. It looks OK, and the fence pro who saw it thought it was a good fence.

Now, here is how the pro did it on my next fence (I needed 140 feet done way faster than I was going to do, and it was not really that much on a per-hour basis assuming my slow pace and over-detailed approach) - cedar 4 inch pickets separated by 1 inch. The fence had exposed posts.

He got a 10 foot length of 1/2 inch PVC Schedule 40 pipe (yes I know - how can you draw an arch with a guide that does not have a tight edge?) On the inside of the fence (the side with the rails showing), he put a nail a little from the top of each post on either side, so that the nails represented the right height to guide the drawing of the arch (so on a level fence the nails would be level). He put a pencil mark at the center of the panel 8 inches up from the imaginary line between the nails. He hooked the pipe under the nails and then held it at the center 8 inch mark with one hand. With the other hand he drew from the center to the end in pencil on the underside edge of the pipe. Here is the trick I would not have thought of: He then switched the hand that held it up and then drew the other half of the arch with his other hand. It was actually a pretty good arch and way faster than my approach. Also, sometimes around tricky spots (around doors, etc.) he had his helper hold one end of the pipe against the nail.

He cut it with a circular saw (!) by plunge cutting it into one of the sides and following his line. He did not keep it flat on the boards, but rather kept only the front edge flat while the rest of the saw plate was off the boards. He had to make cuts in both directions - going right to left some and then going left to right some. I have NO idea if this is a strictly pro way of doing this, or if a novice could make a cut like that. It went fast, though, and it looks really good. Another advantage is that while the my template would have to be custom-cut for fences with different length panels, this PVC approach is the same every panel - put in the nails at the same height on the posts, find the center, go up 8 inches, and hold the pipe. No need to do complex calculations for panels that go up hills, etc.

If you are trying to cut a scallop (negative arch), I believe the reverse instructions would work well also.

The most valuable part of watching him was understanding how much less detailed and perfect he tried to make it, yet it still looks good. He knew what is good enough, while I tried to make every cut, every post, every angle perfect. Needless to say, this is very, very hard with wood!

Ty

 

Whoops, after describing all that detail about the PVC pipe, I see now your question was how to match an existing curve. Maybe it can still work:

It is possible the prior installer used something similar to the method I just described. I would get the PVC pipe (very cheap) and test it against the existing fence with its curve height just see if it ends up looking close enough to the existing curve. If so, then you can just use the same method, and it will look the same.