Captain Bondo

You'll have to excuse me if this post lacks a bit of "substance"... I have been thinking about trying to make my own bends - either heavy wall 304 or thinner 321 if i can actually find some, somewhere....


So the obvious problem is that bending thin wall on a tight radius is not easy without a mandrel bender. Mandrel benders are relatively large and relatively expensive- this is why we are stuck buying bends where around 25% of the cost is the actual material and the rest is the bending cost.

Fair enough.


Now, you can make pretty good bends by packing tubing full of sand- but that a big ------ pain in the ***.


So here's my thought- what would happen if you made 2 fittings, one to clamp onto each end of the tube you intend to bend.

Clamp a fitting on, fill the pipe with water. Put the otherr fitting on. Bend it with a cheapass regular old bender. Drain ther water out. Rinse, repeat.


ANy thoughts? obviously the clamp on bits would use o-rings and be engineered to not shoot a hole through the wall in you shop under pressure.

Anyways I'd like to try this, but it's still going to cost $2k or so which is a big risk for something totally "theoretical".

Would be mostly bending 1-5/8"x0.065-0.100 wall stainless.

Am I a tool? Major ------ tool?

jo_gobel

me personallly, what i do for exhausts and needing bends is to have an exhaust shop bend a piece of the next size up from what i am using.


for example... if i am using 2.5" exhaust, have them bend 2.75" in the press bender to the angle i need. end result is a pretty damn close 2.5" bend. cut off the legs of the bend, and you got your self a 2.5" smooth bend, similar to a mandrel bend.


in theory it would work for the smaller stuff to.


just something to think about.

stealthiskey

why not just make a mandrel? and use that with a regular cheapo bender. I don't think the water would work quite like the sand.

Captain Bondo

I hear you on making a mandrel- I haven't ruled out "retrofitting" a cheaper machine, but I would need another cylinder that pushes the mandrel through the pipe at the correct rate, synchronized to the "wiper" - wouldn't I? That sounds tricky.

People must not use water for some obvious reason- I can't see why it wouldn't work BETTER than sand, even well packed sand is probably more compressable than water, water is pretty un--------compressable.

The only thing I can think of is that you need a super-good seal to hold the water in against the pressure of the pipe trying to deform. But if it's just a case of machining some really good caps that clamp on and use seals then maybe it'd work.

Maybe I am hugely underestimating the pressures involved- it;s a bit hard to "model" in my head....

Eville140

I think even when sand is used you also have to apply a good amount of heat to the bend area, one of the reasons the sand has to be very dry. Sealed steel tube, heat, and water might not be the best. With moist sand the hot spot you make where the bend is going will swell and possible rupture. If there was a cheap, easy way to do it everybody would already know about it.
And it takes a ---- ton of force to bend a roll cage, I have a pro-tools manual job and even with it's geared leverage system and a 4 foot breaker bar it still takes a damn good bit of work. And bending up a cage will wear your *** out.

SpankedYA!

I have a JD2 Model 3 bender. Using it I see how the material stretches and such. I think you will be hard pressed to ever make it work. I see guys wrinkle .095 wall in this bender and its a mandrel setup.

Darkelvis

wood form, heat, bend....think about it...or start downloading episodes of hot rod tv. They built a cage a few weeks ago using this method.

SpankedYA!

cage material is thicker and more forgiving than thin walled exhaust tubing.

Captain Bondo

Yeah, like CS is saying, this is thinwall stainless, not 0.093" or thicker DOM like for a cage. Basically I build headers and want to make my own bends. I also would like to avoid heating it of course. If it were thick mild steel we wouldn't even be having this conversation.

CS,
yeah "wrinkling" would be the part that might be unavoidable.... I think to think of a ghetto way to test this... seems like if you really could hold the water in, the tubing will have a really hard time derforming... maybe the inside wrinkles anyways... I need to find a local guy with a bender...

SpankedYA!

I have a 1.75 and a 1.625 die for my bender. Where are you located.