We are installing our first bending rail on a staircase, and have no experience. Are we taking on too much? Are there any resources with instructions or construction aids? Also, will spring-back be a problem? Any help is appreciated.
(Architectural Woodworking Forum)
From contributor T:
I don抰 know what type of rail you抮e going to bend. I'm guessing if it抯 laminated it will spring back a little depending on how tight the curve is. Do you know about rail bending blocks attached to the staircase? If not you might want to re-think taking on this job.
All bent laminations have some spring-back, but this is usually not a problem since the work can usually be forced back into the shape that the forms or whatever holding devices had, and the work will then be restrained by fasteners (hand-rail supports, newel posts, ballisters, and etc.)
You will certainly want to use an adhesive with plenty of open time.
I don抰 know of any instructions or the like. I helped an english furniture maker do one once and we bolted shop made clamping blocks all along the curved walls of this particular curved stairway and also we were using shop made wood laminates, not the commercial ones that nest together.
You're going to need boko clamps, 1 to each bracket and 2 or 3 in-between brackets. Be sure to mark position on brackets. Apply glue to laminations- sandwich together, wipe excess glue, and tape around about every two feet to hold together. Then it gets intense. You will need 3-4 people to work it, and you will only have a few minutes.
Also as you get to each end the rail will tend to twist, you will need to manually twist with a large clamp attached and pop a kicker under to hold the clamp. Be sure to wax the bending mould before hand and do a test run, before the real thing. Coffman puts out a stair manual that covers a little bit on bending, but not completely. Leave it in place clamped up as long as you can - 3-4 days best. Then the clean up and sanding is not a fun part.
We clamp at every riser line. This allows you to actually see what is happening to the rail as it is clamped and twisted, and then spring clamp the areas between. Also be prepared for the rail to get some long grain checking as the wood lets loose. The tighter the radius the more you might get. This won't always happen, but when it does it doesn't mean the rail is ruined. Just fill and sand.
Spring-back is not a big problem on large curves. They pull back when installed to the posts and balustrade. Don't rush to unclamp everything. We leave our curved rail clamped for three full days before releasing. The glue may look and feel dry on the outside over night but inside it抯 still soft. Don't rush and you won't have to do it again.
Another thing you have to watch for is the way you do your cuts for the connections (gussneck, volute, etc). It抯 better to cut twice then do the job all over again. I only do staircases and most of the trim guys that I run into only mess with straight rail jobs, and only a low percentage get involved with curved railing.
I clamp every three inches with cauls that extend below and above the rail. I have made the cauls out of Brazilian cherry because they are so hard. I usually cut the strips thin enough that it takes about 15 to get the thickness in the finish rail. Since I make my own volutes and other parts it gives me a wider number of options as to how I want to design the first three treads.
I like the stacked commode look and my clients like the one of a kind. I make springing volutes and it gives the balustrade a very unique look. I also build them on the job, I have a mobile shop that makes this work for me. It took me a while to get here, but every job I do is a labor of love and I pursue my craft as an art form. I hope this is a benefit to you guys that are just getting started.
Comment from contributor O:
Bending mold is a must, and it抯 the only way to get the clamps to work like they should. I have found that making square horseshoe shaped pieces (nailed in about every foot) make for a great bending rail bracket. They also help when the rail not only bends but twists because you can clamp them vertically and horizontally.