*
How much to overbend curved laminated handrails has always been a seat of the pants-type of estimate for me over the years. One has to consider radius of bend, number of laminates, wood species, inclination of the rail, etc. On a typical curved stairway, with seven laminate 6510 profile rail, with an inside stringer radius of 50 -60 inches, I typically start clamping my bending forms on the middle step, and then each step above and below, I clamp the bending form 1/8 inch tighter radius. So on a typical 17 riser stairway, I will have over bent the handrail one inch to the middle of the rail. Rails with extra laminates get smaller corrections. Then when the rail is released, and springback occurs, my goal is to have it +/- 1/4 inch from the desired centerline.
What methods have any of you that have bent several rails used?
Replies
*
Stan, there's a formula that predicts springback. It was published in FWW perhaps 10 years ago. I have it at my desk at work, and if you'll e-mail me there to remind me, I'll post it tomorrow.
Andy
*Hello Andy: This is off the subject: I don't know if you remember, but you have on file pictures and an extensive explanation of how to layout and build an elliptical stairway that I sent you 3-4 years ago. I never followed up with the rest of the story. Nice hearing from you. Back to topic,, Yes, I do recall the formulae that was for roughly estimating springback. The main part of it was that springback was directly related to the square of the number of laminates. For instance, if you are bending something with three laminates, and then go to say 6 laminates, 3 squared is 9, 6 squared is 36, the six laminates will spring back roughly 1/4 as much as three laminates. 10 laminates would springback only 1/ eleventh. Of course there are many variables not considered, but this is a good starter. Nice hearing from you Andy.
*Yes, Stan, that is the formula, from FWW 116 or thereabouts. And I do remember discussing the eliptical stairs with you, still have a file with your name on it, in fact. I guess that you got busy building stairs?Best,Andy
*Stan, I haven't done too many, nine I think, and do pretty much like you describe. I've also found that the numbers only get me close, and I don't like calculating anyway, so I clamp them up dry, and see what happens after I take the clamps off the bending forms on the treads (not the rail bending forms). We adjust the forms til they seem right, and then tweak them just a little bit more. It's probably just dumb luck, but they've all worked, well except for that one...blew up cause of a bad glue up, my fault too.BTW, what kind of glue do you use? I've been using ready mixed franklin hide glue, but have wondering about the polyurethanes.Bend me, shape me any way you want to...
*Bucksnort: I use titebond glue, not the titebond 11, it sets too fast. I have had real good luck with it, you just have to have all your clamps and everything ready to go, because the quicker you get it clamped up the better.
*Stan, is the titebond 11 the water resistant stuff? I like it in other situations because it doesn't creep much, and sands without balling up.The hide glue has a long open time, and for someone as slow as I am, that's a good thing. It is messy, though. I'm picking quick set stuff off of right now.Glueby, dooby, doo
*Bucksnort: The titebond 11 is the water resistant type. It is faster setting.
*I have never done a radius tight enough to worry about springback- no problems though. I have used the ready-mixed hide glue and Titebond Extend ,both with very good results. The hide glue is nice on projects that are stained dark, but the Titebond had the long working time and no smell. I split the last rail into two seperate glue-ups and left the clamps on for something like 48 hours each time, overkill maybe ,but everything went smooth and held shape well. For other projects-I love Elmer's Pro-bond .Anyone else?
*For bending laminates, I have had good results with DAP plastic wood resin (brownish/purplish powder). Reasonably long set up time. Brown glue lines, though. I haven't done a hand rail (yet?), but an 8'+ outrigger for an ocean paddling canoe is holding up quite well.
*Brad: I have heard that Titebond extend has the least springback of any glue, plus a longer working time. I guess I will have to order some as it is not locally stocked. Thanks for that tip. I will try it on my next glue up.
*I'm with Jason,I like the plastic resin glue for radius work. We recently finshed some curved front cabinets (there is a picture here somewhere) and forgot to build one of the dummys. So we just threw it in the clamps with regular elmers yellow glue. Out of all the curved panels that was the only one that didn't hold the curve of the clamp.Ed. Williams
*From the Dark Side.
*Ed, If it doesn't violate any of your contracts, how about some brand names, I've got some weird stuff coming up.
*Hey Buck,I think it's the same DAP product listed above by Jason. I'll get to the shop on Monday (I've had the flu all this week) and check for sure. I don't think they sell it in California.Ed.
*Ed, no hurry, nothing to bend here but my mind. In another Ca state, Carolina, we can buy anything toxic,Get well soon
*Rather interesting. I'm no stair builder, just a furniture guy, but Elmers, Titebond, and Titebond II are PVA type glues that suffer from creep, one of the symptoms of which are that joints slide about under stress; laminated structures are good examples of a 'stressed' joint. PVA type glues of any sort are not recommended for laminated work, but perhaps for the (mostly) big lazy curves- supported by other structural members, you guys are talking about they're okay. In furniture we go for non creepers such as urea formaldehyde, epoxy, resorcinol, Scotch, etc. I have also experienced 'spring in' more often than I care to recall- where the curve tightens upon release from the mould. If there is a formula out there to,...ahem,...."accurately" predict springback, I suspect it is a fantasy, but I have to admit that I only have my practical experience with which to doubt the efficacy of such a formula. Sliante.
*Hey Buck,Got to the shop today. Still feel like cr@p but I got things to do.DAP brand.The tub sez:Weldwood Plastic Resin Glue.It's a light brown powder you mix with water.Great stuff. Dries hard as glass.Ed.
*This formula thing is inconsistant with my experience. I recently built 2 arches using cedar. Both the same length (about 14') and radius (about 9') with the same number of plys and same ply thickness. Same adhesive..epoxy. The only difference was thickness. One arch was 5 inches thick..the other 2 inches thick. The 2 inch thick arch had vertually no springback. The 5 inch thick one had 2 1/2 inches of springback.
*
How much to overbend curved laminated handrails has always been a seat of the pants-type of estimate for me over the years. One has to consider radius of bend, number of laminates, wood species, inclination of the rail, etc. On a typical curved stairway, with seven laminate 6510 profile rail, with an inside stringer radius of 50 -60 inches, I typically start clamping my bending forms on the middle step, and then each step above and below, I clamp the bending form 1/8 inch tighter radius. So on a typical 17 riser stairway, I will have over bent the handrail one inch to the middle of the rail. Rails with extra laminates get smaller corrections. Then when the rail is released, and springback occurs, my goal is to have it +/- 1/4 inch from the desired centerline.
What methods have any of you that have bent several rails used?