Braking Aluminum

I have a copy of Pollards aluminum boat building book, and I have read it.
It looks like he mostly plans on boats to be all cut pieces and welded.
That's great for big boats or even for some small boats, but braking seems
like it would make more sense if you have access to a brake big enough.
Some of the small boat designs (think shallow draft skinny water boats)
would really benefit from a mostly bent hull. Aluminum sheet can be had in
pieces large enough to make most of a hull out of one sheet. Some cutting
and welding is still needed obviously, but if you could brake the keel,
chines, and bottom of the transom only welding the front and the sides in
the back you would have an inherently stronger and more rigid boat for rough
service.
The problem of course is how do you brake a piece of metal that big?
Yeah I know a giant hydraulic brake would be a good answer for the
commercial boat builder once they have the capital for it, but how does the
backyard boat builder do it? Are they stuck with all cut and welded pieces,
or hauling their sheet to somebody with a giant brake to do it for them (if
there even is somebody with a brake big enough in the area that hires out)?

Reply to
Bob La Londe
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If you could limit yourself to mostly long skinny pieces, and particularly if you never "asked" for more than a 90 degree bend or so, then you could make a brake out of a couple of sections of (big) angle iron and a bunch of C-clamp-ish thingies.
Make your brake by holding the lower angle open side up, with clamps distributed along the length to push the upper angle down into it. Put in your long skinny piece of metal, then run back and forth tightening clamps (evenly) until you get the bend you want.
It's slow, goofy-looking, and imprecise -- but it's also cheap, easily made, and should be effective.
If you want to achieve an actual 90 degree bend you'd need to use U- channel for the lower part, and either augment the upper angle with a rib along the point (to get a tighter-than-right-angle bend), or just fabricate your upper angle to have a 60 degree bend or whatever.
Reply to
Tim Wescott
I think the main reason is stress on the hull. The cut and welded seams will be stronger and take the constant bending better than a simple bent section of aluminum. Keep in mind that all boats flex small boats flex a LOT. Aluminum doesn't like flex but with the cut sheets the flex of each panel can be dissipated better than if you used a single piece. Plus since many of the pieces come together over frame sections the cut sheets get welded to the frame and each other in the same step.
Reply to
Steve W.
I have actually considered some things like that, only I would need C clamps with a 30 to 40 inch throat. I also considered trying to setup something I could just drive over with a truck. LOL.

Reply to
Bob La Londe
I was envisioning something that either was restricted to very narrow pieces, or that required you to fabricate your own clamps.
Reply to
Tim Wescott
I know. Think 5' by 12' (or larger) of .063" or .080" None of the brakes need to 90 or 90+. Some might need to be 80-85.

Reply to
Bob La Londe
What kind of boat are you planning to make? A jon boat made of aluminum typically has lots of longitudinal "stringers" bent into them with a roll-forming tool, or added-on stringers made of bent aluminum channels that were then riveted on. We had one of those when I was a kid.
Small conventional pointed-bow boats traditiionally are formed either by stretch-forming (used also for canoes) or with big drawing rigs to pull the sides of the bow together. Then they were TIGed (heliarced, actually). Today, I understand, they're MIGed.
Without componnd curves, aluminum is too floppy for a boat. When they draw it into curves, which are simple curves, they generally back it up with riveted stringers or those rolled-in equivalents.
I watched them stretch-form aluminum boats at the old Fairchild Aircraft factory in Hagerstown, MD in 1957. My dad had contracted with them to build boats for Sears after they lost some aircraft contracts. At the time I didn't know what I was looking at, but after working at American Machinist for a couple of years, I realized that I had been watching a stretch-forming operation.
Reply to
Ed Huntress
And when you start forming aluminum you have to take active steps to deal with work fracturing of the metal - and that's Big Factory stuff you can't do in your garage easily and accurately.
You have to receive the metal annealed Dead Soft, usually frozen on Dry Ice, stash it away in a big walk-in freezer before you use it, and that dead-soft state expires in a few weeks even when it stays frozen. I know that's how they handle aircraft aluminum rivets - you buck them in place while dead-soft, then the aluminum alloy naturally re-hardens in a few weeks.
And/Or you have to have a way to re-anneal the aluminum between passes through the benders and rollers when you are applying severe bends or multiple operations - that requires a big furnace and a calibrated control system and convection circulation system to prevent hot spots, there's not a lot of room between "annealed" and "molten".
Which is why they designed boats from sheet stock and stampings for "homebuilding" or small shops. You've got to know your limitations.
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Reply to
Bruce L. Bergman (munged human
"Bruce L. Bergman (munged human readable)" wrote in message
That's for 2024. 5052 behaves better.
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jsw
Reply to
Jim Wilkins
Well, as Jim says, 5000-Series is less fussy. It doesn't heat-harden, and, unlike most 2000 and 6000 Series aluminums, it doesn't age harden after heating. Around here, 5052 is, or used to be, the most-used material for aluminum boats. Now I see that they're using 5083 in some applications.
Pollard has developed some techniques for small-scale building of aluminum boats, but they tend to be full of stringers or frames. Unless you stretch it into compound curves, it drums and flops around, without the reinforcement.
I can't think of many places where I'd prefer it to modern wood and epoxy techniques for a small, one-off boat. But then, I haven't tried. My experience in working with sheet aluminum for complex shapes has not been happy. d8-)
Reply to
Ed Huntress
It also doesn't take well to external impacts. I wish I had taken videos of white-water rapids runners jumping in their beached aluminum canoes to pop out the dents.
jsw
Reply to
Jim Wilkins
Suppose you have three 15' lengths of heavy-enough rails (steel pipe, angle, channel, 4x4 or 6x6 timbers, I-beam, truss, etc) to use for ways. Mount them with axes parallel, two above rigidly fixed, one below on the center line (or vice versa). Make a short rolling carriage with guide wheels and top wheels (eg boat rollers) that work against the sides and bottom surface of the top ways, and bottom wheels that will press down against the sheet being bent over the anvil, the bottom rail. Insert sheet, adjust carriage until tight (ie producing a small amount of bend in the sheet) and run the carriage the length of the ways. Adjust tighter, repeat until done. ("Adjust" would either make the carriage thicker, raise top wheels, lower bottom wheels, lower top ways, or raise the anvil.)
Reply to
James Waldby
Yeah, but a boat with a dent in it will still get you home. A boat with a hole in it "might" get you home. And aluminum doesn't dry rot, sun rot, or stress fracture its glue joints sitting on the trailer even after 50 years. Most of the shallow water jet guys are running aluminum. The mud boat guys are mostly running aluminum, but there are still plenty of stitch and glue duck boats out there because its cheap and easy to build. Its all a trade off on what you want. When a stitch and glue boats boot starts getting worn from running mud or jumping beaver dams it is easy to slap a fresh layer of glass and resin on it. Not as easy with aluminum, but it takes a lot more abuse to get that way, and you can always mitigate that by painting the bottom with a good quality air boat hull paint.
For that matter there are some plastic boats out there that will take an incredible amount of abuse... BUT (note the big but) after a few years in a UV rich environment like anywhere in the Southwest they will get hard and brittle. Even if they don't get much use they will crack at the "hard points."
Reply to
Bob La Londe
Commercial boat builders (in some cases using what I would consider the wrong alloy) make long brakes in aluminum all the time. Most small boats have rolled or bent ribs in the hull for strength.

Reply to
Bob La Londe
5052 seems to be the most popular alloy for hulls, with some builders liking 5086 for structural components, and very much so for larger boats. Some of the backyard mud boat guys are talking about using 5086 for hulls as well for its greater strength. I'm not sure its all that much gain in thin hull material, but...

Reply to
Bob La Londe
The 5xxx series are work hardening, the more abuse the better. A few years ago I repaired a canoe made in the 50's that was knicked by a snowplow. It sure was tough stuff! Almost like stainless, it was so tough! ;>)}
Reply to
Phil Kangas

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