I want to use cant rails and then featherboard. I can't work out how I can fix the cant rails to concrete posts.
I have seen gates hung on intermediate concrete posts where a piece of 2x4 has been bolted to the concrete post. I'm wondering if I could bolt a piece of 2x4 to both sides of an intermediate concrete post and then screw my cant rails into the side of the 2x4?
I did this for a gate with 2x4 using long screws and rawplugs. There is less concrete to screw into, but the good thing is that you tend to miss the steel reinforcing bars which aren't usually down that narrower, central piece in my experience. I have to say that the gate itself was hung on a wall though - the 4x2 was for the bolt side, so didn't have to take any weight.
What you want to do would work in theory, but I can't help feeling that making your own panels will be less hassle, especially if the concrete posts and gravel boards are already in place ? By the time you'll have done what you're proposing, you'll have effectively made panels but with the added hassle of having to attach them to the posts, rather than sliding pre-built panels in from the top. Just my thoughts anyway.
I've had some standard size vertical featheredge fence panels made for me recently, plus I ordered the bits to make some of my own non-standard panels. Once you see how they're constructed, it's a lot easier than you might think to make your own, especially as the batons and top cap can be bought in 6ft lengths and the featheredge boards in any length you like (4/5/6ft etc) - no sawing required !
Another Silly question probably, but if I get 3 cant rails fitted how far above the top cant rail can the featherboard extend ? I have only seen it advertised up to 1.8m long but wondered if I had 6 foot of post above ground, 12" gravel boards could I have a foot of featherboard above the top cant rail to make a 7' fence height?
Featheredge fence panels tend to have a baton along the top edge, with a top-cap nailed to the baton in order to protect the top edges of the featherboards, so it might make sense to do the same.
You could have them stickiing up above the top rail, but they'll be more exposed to the elements and you risk them warping or deteriorating more quickly than they would if they were protected.
Bear in mind that anything over 2m requires planning permission and that figure is less if it borders a public highway IIRC.