Diy Bending...
 

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 ass.


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?

Re: Diy Bending...
 

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.

Re: Diy Bending...
 

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.

Re: Diy Bending...
 

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....

Re: Diy Bending...
 

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 ass out.

Re: Diy Bending...
 

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.

Re: Diy Bending...
 

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.

Re: Diy Bending...
 

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

Re: Diy Bending...
 

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...

Re: Diy Bending...
 

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

Re: Diy Bending...
 

No, that is not a mandrel bender, a mandrel bender has a mandrel/die that goes on the I.D. of the tube to maintain the I.D. on the radius.

Re: Diy Bending...
 

To answer the water thing, you can't. The reason being is that the tubing does need compress in the radius. Filling it full of water will not allow it to compress and by either adding more ram pressure(I don't care how strong you think you are you will need hydraulics) or heat to complete the bend you will merely just blow the tube up, literally.

Re: Diy Bending...
 

Thin wall / Tight Radius cannot be bent on anything but a mandrel bender, and it's not just any mandrel bender that will do it. As the "D" (ratio of tube outside diameter to radius) of the material gets closer to 1, the bender has to become more sophisticated, so it gets even further complicated w/ pressure die assist, direct pressure profiling, boost pressure profiling, early extract points, etc. The material has to be literally pushed and boosted around the outside of the bend. The mandrel itself is only part of the system that prevents the wrinkles or tube collapsing. There is so much more to it.

If you go to page 15 of omni'x mandrel bending guide here (http://www.omnibend.com/pdfs/Omni-X_...ding_Guide.pdf), there is a chart that will help you calculate what you can and cant bend with a normal rotary draw bender, and even just a normal mandrel bender. Say you wanted to bend 1.65" stainless w/ a .065 wall thickness, you would divide 1.65/.065 = 25. Then you go over to your radius chart and look for the first radius that doesnt require a mandrel or wiper. In this case, it's 5D (radius = 1.65*5= 8.25" CLR) can be bent without mandrel or wiper. So any single shot rotary bender could do that. But notice you have to increase your wall thickness to say 0.095 (1.65/.095 = 15) if you want to bend that on 4D radius. Then of course the other problem is, the larger your wall, the larger the torque requirments on the bender. When you start getting to 0.095 ss-304 ... Most normally rotary benders are going to come up lacking in torque. Not to mention .. How useful is a 8" CLR for headers? Not very... (That's a 16" u-bend between centers!)

Re: Diy Bending...
 

I have a copy of the article on sand bending... somewhere. Be prepared to go through some oxy-fuel as you need a lot of heat.

Re: Diy Bending...
 

The heat / sand bending technique is basically used in the industrial world with induction benders, where they super heat the material and draw it on a pivot point sometimes over a mandrel as opposed to capping the pipe with sand. Although this works, it won't do thin wall on a tight radius. Most induction bends are 3D or larger.

There's a beautiful picture of an induction bender here:

http://www.pipebending.com/

Re: Diy Bending...
 

I think I have a couple of them out in the barn, will check later.

Shame there isn't a place that sponsors this site and even gives discounts on these types of materials. And I bet if buying in bulk they might even give a better price? maybe?

Hmmm, shame there is nothing like that.

Re: Diy Bending...
 

Passenger,

I got ya I think- I can see why you can't just load it up full of something completely uncompressible and expect it to cooperate. Cheers.

Columbia,

Super educational posts, very much appreciated!

Eville,

For all of the 16ga stuff I do, my bends currently come from Racing Solutions/Columbia, just for the record.

The point is that if a guy's volumes keep going up, at some stage it makes sense to start bending his own. Don't misread this to think I'm trying to be some sort of dickhead - that's not it all all. I just want to try to run an efficient business - bending my own and being able to do things like pre-bend the more simple runners in one piece, etc. could save me a lot of time and costs, and that means doing it myself ideally.

My best bet is to probably stay on the lookout for a used mandrel bender I guess. ;D

Thanks guys!

Re: Diy Bending...
 

since i mandrel bend pipe for a living, once you see how one works, you'll quickly realise how you won't be able to pull anything off using a crush bender

mandrel bending is basically extruding the pipe over a mandrel versus just compressing it around a die like a crusher

Re: Diy Bending...
 

I've watched a two stroke guy fix a dented exhaust by capping one end, pressurizing the other with shop air, and geeeeeeeently heating the dented area. I think you could manage to uncrush some crush bent by this method.

Re: Diy Bending...
 

http://www.fluidfabrications.co.uk/j...ndMandrelh.jpg

http://www.bifabuk.co.uk/images/Mandrel_Tooling.jpg

http://www.bendtooling.com/product%2...bronze%202.JPG

http://www.fordmuscle.com/archives/2...es/lineart.gif

probably the easiest HMT sort of thing to build now that i think about it. i think i'll put my big ------- hydraulic ram to use on somethin like this >:D >:D

Re: Diy Bending...
 

That's sort of like hydroforming without a dye.

Re: Diy Bending...
 

Yeah- that's where I've been headed- "Ok then, can I build a mandrel bender?".

I have been looking at taking a similar approach to what guys do building regular benders- buy some tooling, build the rest.

So basically pick a rotary draw machine with a design that lends itself well to adding a mandrel- no huge deal I don't think.

The mandrel is easy enough- but the wiper die is a pretty sophisticated piece.

I will probably build it with the thought that I may need to retrofit a wiper die, but just try a mandrel at first.

Some mandrel benders "boost" the material around the die, things can get complicated fast, but my thought is that if a guy just built a more deluxe version of a standard bender and kept evolving it, he might be ale to get something decent.

I am thinking I will likely go to 14 gauge (0.083") material for the headers as a nice compromise between 16 gauge and schedule 10- one benefit is that it should be slightly more forgiving when bending.If I can come up with a way to bend 1-5/8" x 0.083" stainless on even a 3" radius (6" between the legs on a u-bend) I will be in great shape.


I am thinking about basing it on this bender:

http://www.mittlerbros.com/tube_bend..._hydraulic.htm

They have extremely detailed assembly drawings for it on their site, along with parts lists.

I'd likely buy the gear/rack assembly and maybe the shaft from them, and a 1-5/8" die set. Then I'd have a smaller radius 1-5/8" bend die made (my brother is a machinist, yay!) and set up a mandrel.

It's basically just a 4'x4' welding table with a 3/4" thick steel top with drilled tapped holes for the tooling, bracketry for the hydraulic cylinder below, and that's it.

Famous last words... ;D

i need 2.5 bender

does this work?

somebody called?
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