I have already built two bicycles, a lowrider and a beach cruiser.
Although I made everything from scratch, I have never managed to bend the tubes myself. I had to go to a local shop and have them bent and the job payed for.
Has anybody done that at home? How can I bend the tubes in my garage without hydraulics?
A wood mandrel with a groove cut in it + a cheater bar and you can bend whatever you need- provided that the radius isn't too small. Smaller tubes like fork blades and seatstays have walls that are proportionally thicker than main frame tubes and bend nicely. The larger diameter tube you have, the more you'll need some internal support.
What are you wanting to bend?
Again, it depends on what you're trying to bend. The sand works really well on main frame tubes up to 1 1/8" with at least an .035 wall, I've bent quite a few of those on a 22" radius. Larger diameters with walls that thin really need more support than the sand can provide.
What about heat? Should/could the tubes be heated during the process, or is that a different independent techique?
I want to bend a 40mm in diammeter and 1mm in thickness main frame tube. I want a smooth curve.
It is for the top tube of a stretched cruiser frame.
Heat is not a great thing. It takes between 1500 and 2000 to plasticize metal so you get some give, normally a temp in the orange range. Check out the Chopperhandbook.com site for downloadable plans and I made my own bender threads. If you want to do 90 degree bends like one finds on frames, then you need an inside and outside die. These can be two round wheel like dies. I have used found wheels for these. Check out Dave Gingery site for wooden wheel dies.
I'll check it out.
Anyway, the best way is to build a wodden mould on which to bend the tube, right? Should I use a rubber hammer to "gently" help the tube to bend?
That's a pretty big tube to bend this way. I've tried a 32mm x .8mm tube packed with sand on a 2 ft radius mandrel and it worked fine once, then kinked a bit the second time( I think I needed to pack it better) . I've never done one as big as the one you have- it does help that it's a thicker tube- I'd give it a 50/50 chance at working.
You bend with leverage and brute force, a mallet won't help.
As an aside, 28.6mm tubing will bend great and looks "right" as a tt on a steel frame.
edit: I just read that your frame will be stretched, the 40mm is probably a good call.
TO get the force you can buy the tube overlength, then wrap it around something very solid that you can bend it around. It takes a lot of force to bend a tube and it can be quite a business to secure your "mold" strongly enough to resist the forces involved.
When you use this method you don't need sand in the tube.
You don't need this kind of thing to put purely aesthetic long curves in, though this kind of deal works well, just give it a nudge every few inches to get a shallow curve. These dies will bend 90 degrees.
Keep in mind that if you double the size of your tube it is 8 times harder to bend.