If you're going to leave those post up above the top rail you could screw those to the 2x4's on the ends & toe screw up from the outside of the rail into the top cap. Only the screws on the ends would show.

All that said I would rather use a 5/4x6 board for the cap. Cut the post off flush & run the cap over the post using headcoat screws straight down, it makes a stronger rail that way, but that's just my perference.

Al

Thanks for the reply Al. I really like the look of how the extended posts break up the lengths of railing and was planning on leaving them up and capping them somehow. Especially since I already have all the material to cap the rails with 2x4. Do you have any pics showing 5/4x6 cap and flush posts?

JT it would be possible to bisket joint the 2x4s to the top rail using tightbond 111 and a few clamps, a person could do it with out the biskets but...well you know...I just love using that machine!!

If you dident want to buy a whole lot of clamps you could just get like hmmmmm let me look up there------say 6 clamps and do the work in sections. Clamps are very good to have around I have several walls covered up with them and I never have enough!!! J.

Great idea John. Unfortunately all I have is a half dozen pipe clamps which wont be deep enough.

I think I may have no choice but to just use plugs to hide the countersunk screw heads.

Anyone else do it differently?

Deckman called it:
On your existing 2x4 top rail - using a countersink bit, predrill a hole 1" below the top edge at an upward angle every 18" or so.
Install your cap rail by running (2) 3" screws per end into the adjacent post (Run screws up from bottom edge of 2x4 cap rail into post to hide those screws). Better predrill those holes too.
Run 2" screws up through the angled pre-drilled holes to secure the entire length of the cap rail.

No visible fasteners from on the deck (you'll be able to see the holes in the top rail when you're out on your lawn).
Another good thing about NOT top screwing is less chance for rot (no topside penetrations means less spots for water to enter)

Let me know if you don't understand this...

Mac