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PostPosted: Wed Apr 20, 2016 3:23 am 
knight of the folding kayak realm
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Location: inland Pennsylvania, USA
Any suggestions would be welcomed for straightening some badly curved frame sections on my Feathercraft Wisper. The folks at Feathercraft suggested placing the parts in a vise and trying to physically bend them but I have my suspicions that won't be simple, or even work at all. My understanding of aluminum is that it has a crystalline structure that becomes "work hardened" when subjected to stress after extrusion -- so bending it means the metal of the bend is now harder and more brittle. Heating does not gradually soften aluminum the way it does other metals -- it requires heating it to near melting and then it just goes floppy and has to be re-annealed.

The boat got hauled too far and for too long on a roof rack that was too closely spaced when I was up in Quebec late last Summer (we had to bail in a monsoon-like thunderstorm and I didn't have the option to break down the boat before loading it on somebody else's vehicle in the shuttle). The whole bow droops down so badly now that the central bar on the bow deck will no longer reach the rib it is supposed to lock into ahead of the coaming. The entire boat has reverse rocker! Obviously performs very badly. I guess I have nothing to lose trying to fix the parts before dropping several hundred on new frame components. Anyone have experience doing this?

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PostPosted: Wed Apr 20, 2016 7:51 am 
lord high faltbotmeister

Joined: Thu Sep 06, 2007 8:05 am
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KoK,

Sorry for your troubles. I am surprised that FC would advise you to put the tubing in a vise. That will not work. As you note aluminum is an element that will not submit to brute force. You can probably return the tubing to its original shape with a proper tubing bending tool, but they are very expensive...if you have a machine shop in your neighborhood you might try to get some help there. Best of luck!

g

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PostPosted: Wed Apr 20, 2016 11:16 am 
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Second Greg's suggestion. You live in Pittsburgh and I'm reasonably certain that you can find a well equipped machine shop operation in the area. I think that trying to use a large bench vise would only put another bend in the existing bend.

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PostPosted: Wed Apr 20, 2016 11:17 am 
lord high faltbotmeister

Joined: Fri Oct 07, 2011 1:51 pm
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Location: Colombo, Sri Lanka
Personally, I don't think this is anything to get too alarmed about. The amount of bend will be small, probably less than 10 degrees, so you won't need a tube bender. Start by putting the bent tubes on the floor with the bend up and standing on them to straighten them as much as you can. I'd do this with several connected tubes to avoid partially distorting the joints if possible, but it's no big deal if you're careful. Then suspend the each tube between two flat surfaces at the same height. With the bend up, gently lean on the tube with your weight on your hands until you get rid of the last little bit of bend or near enough. Roll the tubes on the floor to check they are more or less straight.
I' ve done this with my Airfusion to get the keel straight again after it banana'd taking it out in rough water before I fixied the issue for good with a extra sleeve tube over the central part of the keel.
Don't worry about crystallisation of the aluminium, these alloys are maleable and it's not as if you're subjecting it to extreme stress or strain; bear in mind that the bow and stern tubes were bent cold in pipe benders and they aren't known to break.

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Pakboats Quest 135, Nautiraid Narak 460, 416 & K1 (sold my 550), First light 420, Feathercraft Wisper, Fujita Alpina AL-1 400, Incept k40 (for sale)
Non-folders: Cape Falcon F1. Beth sailing canoe, 2014 Hobie Adventure Island


Last edited by siravingmon on Wed Apr 20, 2016 11:55 am, edited 1 time in total.

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PostPosted: Wed Apr 20, 2016 11:37 am 
Brotherhood of the Golden Paddle

Joined: Mon Apr 18, 2005 3:40 pm
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Location: isles of scilly UK
Simon is spot on, take care not to try too hard and "kink" it. Annealing is very easy but if done it will be soft and bend VERY easily which you don,t want. Don,t try to anneal, just above that heat the aluminium melts and disappears. I have annealed aluminium at work many times to avoid from cracking when being bent.


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PostPosted: Wed Apr 20, 2016 12:10 pm 
knight of the folding kayak realm
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Thanks so much for the advice and encouragement. I would prefer not to have to remove the shock cord (I've rethreaded enough sets of tent poles -- kind of a pain) so heating is only a last resort.

I do have experience bending metal tubing (was an industrial construction electrician for many years). If I could find a bender of the right diameter I imagine it would be a familiar operation. Maybe I will see if there is an auto accessory fabricator in town that could handle it if the manual technique is unsuccessful -- I'm thinking one of those shops that makes custom car and motorcycle exhausts and fittings?

Am also thinking that if I can find a heavy steel or iron tubing that is slightly larger in ID than the frame parts OD I might be able to mount that in my bench vise and slide a frame section in as far as the bend so I have a sturdy base upon which to be able to exert progressive force to straighten it inch by inch. When I worked construction I used to be able to straighten overbent rigid galvanized conduit by sticking the piece into a small hole in a concrete floor and then leaning on it. Of course, galvanized steel is more malleable than aluminum. We did occasionally bend aluminum conduit and I recall it being much more difficult. The trick to not kinking tubular stock is to have it constrained by a snug fitting circular enclosure close to its original OD.

There is actually a TechShop here in Pittsburgh, one of a nationwide chain of fully equipped machine and fabrication and design shops where people can pay a monthly membership fee and have access to every type of equipment one could imagine including CNC milling, 3D printers, full welding and woodworking shops, powder coating gear, industrial sewing machines, laser cutters and water-jet cutting tables. I seem to recall they had a range of tubing benders as well. I just toured it again last weekend, with my nephew who was in town for a prospective student interview at Carnegie Mellon University. Since i retired recently, I have been thinking of signing up. Would like to build my own kayak eventually and this place will be ideal for that.

I'll let you all know how it goes. Thanks again!

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PostPosted: Wed Apr 20, 2016 1:01 pm 
lord high faltbotmeister

Joined: Fri Oct 07, 2011 1:51 pm
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Location: Colombo, Sri Lanka
Just a couple more things.

Good idea to look for a piece of sacrificial tube to protect the ends. This can be internal or external, aluminum or steel. Closely telescoping tube in the US is 15 guage - that's 0.058" wall thickness.
The Yostwerks site has a good guide for this here http://www.yostwerks.org/Gap.html.
His site also has a good list of suppliers for aluminum tubing here http://www.yostwerks.org/ContactsFrame.html
I used these people http://www.texastowers.com/; they weren't expensive but the shortest length was 6 feet. Make sure the tubing you use is extruded not welded or it won't telescope.

Tube benders do only fairly small radiuses so check that the radius of your bent tubes is not actually muche larger - quite possible in my opinion

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Pakboats Quest 135, Nautiraid Narak 460, 416 & K1 (sold my 550), First light 420, Feathercraft Wisper, Fujita Alpina AL-1 400, Incept k40 (for sale)
Non-folders: Cape Falcon F1. Beth sailing canoe, 2014 Hobie Adventure Island


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PostPosted: Wed Apr 20, 2016 2:43 pm 
faltbootemeister
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Trying to straighten a long, gradually bent piece of AL tubing is very tricky. It's a great way to kink it or, if there are holes drilled in it anywhere, to break it at the hole.
The safest way, without heat (which cries for a metallurgist), is a 3-sheave device. The sheave's pulleys must be sized to the tubing OD. The spacing between the sheaves must be set to apply straightening force to the tubing without kinking. That's the distance between the sheaves as well as the difference in height or out-of-plane-spacing between them. You simply set it for very little bending force and roll the tubing back and forth through the pulleys as you slowly bring them closer into the same plane. Not an easy rig to set up at home.

If you're really good, you can do it with two sheaves. Takes experience and a good hand.

I'm sure this wasn't really of any help. Just thought I'd throw it your way in case you've ever seen a trombone slide repaired after being bent. The good guys do it by hand with a giant gauge block.

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PostPosted: Wed Apr 20, 2016 3:35 pm 
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First the good news: the 5/8" tube used for most of the frame does respond favorably to slow heavy pressure when locked in a vise. I managed to straighten the bow top tube (the worst of the lot) -- still has a faint S-curve in the middle of it of less than a half cm offset but at least the main lengths of both ends align and it should lock securely into the slot receiver in the rib again. I was similarly able to straighten the two top chine bars on the bow section and am confident the lower pair will respond to the same attention. None of the keel bars got bent so they're not an issue.

The bad news is that the top tube in the stern section is 3/4" tubing and it will not budge. I worked on it for over an hour and made no progress. So it may need to be replaced in the end. I'll try setting up the boat after I get the other sections in reasonable shape -- it might not be that big of a deal to have a downward bowing in that piece but if it is I will just order one. Last time I got a frame section from FC I think it was around $80 with shipping and handling. Ouch! but better than a whole new frame.

Another bit of bad news is that my crappy Sears 4 1/2" vise has a blown out base (it's one of those that is supposed to be rotatable in the horizontal plane but it won't lock down -- teeth must be stripped or something.) All it was good for in this project was providing a gripping pivot point against which I could apply pressure in opposing directions with the tubing locked in the jaws. Not a big deal -- it came with the house on the workbench the prior owner left behind. I never would have bought a Craftsman vise, or any tool from Sears, for that matter. You don't want to get me started on cheap tools that break all the time. I don't care about their "free exchange" policy, I want stuff that doesn't break in the first place, besides which Sears closed the last store in our area two years ago. When I worked in the field and my ex had a car repair garage I used to have to take a bag of tools to Sears every month to trade in -- split sockets, cracked wrenches, bent screwdrivers, splayed hammer heads. I know it wasn't us misusing them because once we both switched to Mac, Snap-On, Greenlee and Klein tools nothing ever broke again.

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PostPosted: Wed Apr 20, 2016 3:42 pm 
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I do recall how specific the bending shoes and sheaves were for the various sizes and types of metal conduits I used to work with, both the manual benders and the hydraulic ones. It was a common boo-boo in the field for newbie apprentices to end up crushing a length of EMT or IMC (intermediate metallic conduit) due to trying to bend it not only with the wrong size shoe but in a set-up designed for a different material, like galvanized rigid. The pulleys and sheaves and shoes have to be EXACTLY sized and aligned to control how the material will stretch and reshape.

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PostPosted: Tue Apr 26, 2016 9:33 am 
Brotherhood of the Golden Paddle

Joined: Sun Aug 16, 2009 10:05 pm
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Perhaps it's a bit late in the game for this suggestion but I would probably have tried bending it back into shape using the same process that bent it out in the first place. With the boat assembled support the two ends... and this should probably vary through the process... then gradually add weight to the center until you achieve the shape you want... let it sit in the sun for a few days... add water... it worked going one way, should work going the other. It's all about managing the process.

at least it's what I would try first.

I've never had good luck with vices (or most gripping tools for that matter) and aluminum.

d

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PostPosted: Tue Apr 26, 2016 12:20 pm 
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I doubt that would work. The dynamic force applied by 40 mph winds on the boat atop a vehicle going 60 mph would have been much higher than any passive wieghting pressure could apply. I did consider inverting the boat on the roof rack and driving up the expressway for a few hours but feared all I would do is pervert other frame components. Tin or lead might soften in prolonged intense sunlight, but not aluminum.

I think I have it straightened enough to function -- been too busy to set it up but may do so today if the rains hold off. I don't have a garage or shed so such operations have to take place out in the yard.

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PostPosted: Tue Apr 26, 2016 11:00 pm 
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Look forward to hearing how you fare... the sun part was kind of a dumb joke... along with the water, although water could become a great weight... nice and even.

d

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PostPosted: Wed Apr 27, 2016 10:31 am 
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I may find out today if my rebending efforts have corrected the malady well enough to make the boat assemble correctly. Depends on the "occasional thundershowers" they have been predicting (not that the boat will care about getting dumped on, but I might.) I have still, with repeated efforts, been unable to budge the thicker stern top tube, but the thinner frame parts do respond to heavy pressure.

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PostPosted: Wed Apr 27, 2016 11:58 am 
faltbootemeister

Joined: Tue Feb 05, 2013 1:15 pm
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Hi Kerry,

I don't know if this will help you much except maybe give you hope. Years ago I purchased the "rolling rib" for my Kahuna. Because the top of that rib is lower, over time the thick stern deck tube developed a slight bend, subtle but definitely not straight anymore. I'm not so sure if I went back to the standard rib that the deck bar would fit. Maybe it's possible that the tubing on your Wisper will bend back over time from use. Maybe that's wishful thinking. There are two times that I winced reading this forum...when Tsunami Chuck told about the time airline goons threw his Khatsalano to the tarmac and your account of the Wisper.


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