On Fri, 30 Dec 2011 16:31:58 -0700, Bob La Londe wrote:
"Tim Wescott" wrote ...
On Fri, 30 Dec 2011 16:14:49 -0700, Bob La Londe wrote:
"Tim Wescott" wrote in ...
On Fri, 30 Dec 2011 12:22:53 -0700, Bob La Londe wrote:
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
[...]
The problem of course is how do you brake a piece of metal that big?
[...]
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.

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.

I was envisioning something that either was restricted to very narrow
pieces, or that required you to fabricate your own clamps.

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.

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.)

--
jiw