Bending a cap rail for a curved railing
Hello all,
Been a while since I’ve been here – life’s been good and I’ve been busy! I’m working on a TREX deck right now that I curved the handrail. Top and bottom rails curved nicely because they were TREX 5/4×56 decking on it’s side.
So far I’ve busted two 5/4x6x20 boards attempting to curve them on the flat. The first one I broke because I only had one strap pulling it right at the center. The second one I took three days of continual pressure from 5 straps to pull it into shape. On the third day, I noticed a little tear near the center of the board. I pressed down on the board and it just snapped. Weather hasn’t really cooperated – staying in the 60s-70s. I had a portable heater heating the center of the board.
The radius was 102″.
What say you, Breaktimers? Any thoughts on different material for the cap rail? I talked with the homeowner about three ripped sections of 5/4 bent separately, then screwed together on the radius shape. He really wants a unbroken look for the cap rail.
I’m thinking about the cutting 3/4″ grooves in the underside of the cap rail every 1/2″ or so across the inside 4″ of rail and trying again. That way, the outside edge is unbroken and there’s space for the board to compress into. The inside edge would have lines every 1/2″ but the material would be compressed so they would be lines, not gaps.
Anyone done something like this?
Thanks in advance for your thoughts –
(And no, I don’t particularly like the pt posts with the TREX rails. It was a fiscal decision made by the owner. He’s going to paint them white to match the cedar balusters.)
Mac
Replies
Wow that looks like fun. I hope you have a little extra in there for experimentation. As far as I can see there is 3 ways you could make that bend: 1. kerf the front edge to relieve compression while making the bend,
2. use a steam box. 3. make rips out of the piece and glue them together.
The first one I think will work but probably won't look very good because the kerf would have to be through the entire board and calculating the right amount of stock removal to get it just right would be beyond me, so I wouldn't go that route.
The steam box probably, if executed properly, would give you the best result, and would probably second most labor intensive, but I've never really messed with one. So I might, but probably wouldn't choose this route either. Because I would hate to put the time into it when I'm only pretty sure it would work.
So I would opt for the last. The key to this I think would be the ability to bend it around a mold. When we bent rails for interior staircases we used a plywood jig. It was basically a plywood T with a 45-degree strong back on one side made out of about 4'' rips. Both pieces of the T about eight inches. This piece will be used to anchor the bent rail against. Now you will need some 8''X4'' pieces for the other side of this clamping jig. Now if you set the assembled T with strongback in front of you upside down with strong back to the left (this is the fixed side of the jig) and take one of the 8''X4'' pieces and set it next to the upright to the right. these two pieces will make the clamp. All you need now is a way to tighten the clamp. You will need some J-bolts. Drill two holes in each of the pieces laid out in the same place. Slide the J-bolt through the T and through the other piece, Now you can bend the rail through the jig and tighten with the J-bolts. This is how we did hand rail.
Your situation being 5/4 X 6 I might even forgo the J-bolt scenario and just use clamps if you have enough. Although it will be much easier with the J-bolts. Key to it is some where to lay out the radius so that with a screw or small lag the jig can be plotted so that the radius will be true. Draw the radius line and screw the jigs around it. Position of the jig is critical. Align the fixed side inside edge with the radius that you want on your outside rail. If the edge of your deck is 102'' radius you'll have to add if your handrail goes out past the edge. You'll probably get away with three rips to make that bend, a little over I-13/16.
This method is pretty labor intensive, and I imagine a lot of guys would just go out and start to bending. I prefer knowing that my work is going to have a predictable outcome. Possibly some one else could come in work next to me and pull a board into place while I was still making my jigs but then again maybe not. I think you will know by the feel if you can bend it without one of these more elaborate approaches.
There is still the problem of glue and alignment. The glue I would check on but the alignment can be done during the bending. This is why the bending jig with the J-bolts works so well because you can get all the rips in the jig before it is completely tightened. a slow tightening and maybe some auxiliary clamps with some straight strong back to keep the rail from cupping will be a great help. I hope this helps and also maybe someone will come up with a better scenario.
After rereading this I still think you have your hands full and it doesn't look as fun as it did at first glance. Good luck
Mac,
It's gonna take time but your gonna need to to make a jig with the specific radius.
Rip and glue up your stock. Remember to leave extra room - the rips get 'shorter' as you glue up the layers in the jig.
Enjoy,
Saint
Trex is made to bend that way. I have seen pics of it done on deck flooring. The trick is Heat. Rember trex is mostly plastic, get it hot enough and you can turn it into a pretzel. Contact trex and ask them how they would recomend heating up. You might need to make an inside curve template to bend the rail to after it has been warmed up.
I have recently done a simular rail with a 5' radius. I used 5/4x8 Azeck.
Azeck sells a heat bending kit that gets the material to the recommended 300º, then the stuff is really flexible.
Being their kit costs about $1000, I just built a plywood box with salvaged electric heaters in it, which worked pretty well.
Did you heat the entire board in the plywood box, then bend it all at once? Did you use a jig to bend it after it was heated? Was the plywood box segmented?how close were the heaters to the product? would you send me a pic of your box or a description of it? I will probably build something like it so that I can do this for future composite decks I build.Thank you for your time in replying,MacView Image
Steam or NH3 are the only options I know of for a solid wood rail bent like that . Both would be a task . I think that ripping the board into strips no wider than they arer thick . Mark the center and number the rips keep them in order. glue up around a form . Pulling from the middle ,keep the center line straight . use lots of clamps . And good water proof glue.
The other option would be to use the trex for the cap . The other day at RP lumber the Azek guy was there with a sample of 5/4x4 bent in a spiral of about 1 1/2 " radius . He also had samples of shaped azek that were bent flat after they were shaped . That could be anothe r option
I didn't specifically say in my first post but the cap rail is TREX. I wouldn't even take on the job of trying to bend a wood 2x6 to this radius!Thanks for the suggestion though,MacView Image
No matter what approach you take the deck looks like it has some real potential and I would like to see a final pic. And the guy who gave you the advice about calling the manufacturer to find out about bending is right on.
TREX is on my list for calls Tuesday. This deck was for a buddy of mine who's going to finish installing the balusters on the rails I build for him. I'll finish up my end on Monday and take some pics.MacView Image
Read up on this at http://www.trex.com tells just how to do this.
Mac:
Below is url from Trex's site, has specs for bending.
http://www.trex.com/products/installation/pdf/Special_Applications.pdf
Note that it's a PDF and requires Adobe's Acrobat Reader to open, avaliable as a free download from Adobe at http://www.adobe.com .
Looking forward to seeing the photos of the finished deck.
Regards,