Bending Stainless Steel Pipe.

[Paul W]

I'm looking at making new anti-roll bars for my car a little stiffer than the curent items. I've sourced some 3/4 inch stainless tube but wondering before I rent a pipe bender (Usually just used for copper pipe) if it will be possible to bend the pipes.
Has anybody used one succesfully before ?

[John]

I dont think this steel is going to make for a good sway-bar. The reason is that it may not have the spring qualities that a sway/anti-roll bar needs. It all depends on the grade of steel; though, you don't see many stainless steel springs outside of very specialized applications.
Why stainless anyway? the cost for spring grade stainless is going to be huge, and probably perform less than a non-stainless bar.

bending tube on a pipe bender is going to be a problem as well. I might have this backwards, but pipe is measured on the I.D and tube is measured on the O.D. This means that the dies used for bending copper water pipe are not going to fit tubes.

You also cant go bending spring steel with out heat. This is a problem since when you heat it, the spring is going to lose its temper. Thats why a lot of sway-bars for race cars have splined ends which removable arms attach to.

[Paul Bearman]

I wouldn’t recommend using stainless steel. Use a 4140 chrome molybdenum steel or a high carbon steel such as EN24 & heat treat to achieve the required torsion.
4140 is in the range of 0.37% to 0.43% carbon but this is an American spec steel & more expensive than the EN range of steels here in the UK. EN19 is a chrome molybdenum alloy equivalent to 4140 and so is useable for the kind of hardness required.
EN24 is a high carbon, nickel, chrome, molybdenum steel alloy, very similar in composition to 4340 & has a general carbon level of 0.4% & is ideal for heat treatment & the preferred choice where applications demand high strength & resistance to shock.
0.4% carbon steels can be hardened to a maximum Rockwell "C" 44 but above 46 they become to brittle, 38 is about the minimum hardness for anti roll bars & this will give a tensile strength in the order of 170000 psi to 194000 psi. Without heat treatment it could be as low as 70000 psi. However, generally, hardening and tempering to anywhere in the range 38-44 will do the job.
Deciding on the material spec for the anti-roll bar is not the only consideration. Other important factors to consider even before parting with your hard earned cash are: centre of gravity height; roll centres; roll rates; roll couple distribution; spring rates; anti-roll bar rates; shock absorber rebound/compression rates; bushing durometer ratings; tyre size, suspension alignment specs .... the list of interacting variables is endless.
The only job of the anti-roll bar is to handle roll resistance & this can be determined through the mathematical formula:
R = [(pi)(G)(d^4)] / [(16)(b^2)(L)
where R is the roll rate in pounds per inch, pi is 3.14, G is the modulus of the material; d is the diameter of the bar; b is the length of of the roll bar arm measured from centre to centre; and L is the length of the anti-roll bar.
Generally, the diameter of the bar will have the greatest effect & small changes in bar diameter result in large changes in anti-roll bar rate since it varies as the fourth power.

[Frank Catt]

Paul, 22mm dia Special steel we use.

[Phil]

Paul
Take a look at the roll bars available in some of the race catalogs. There are straight lengths available in 1" increments, with various diameters. Also available are some really nice arms splined for the bar, with connections for heim joints at the end. Most of the arms can be had in straight and various bent configurations to fit your chassis.
If you really want to get crazy you can get an arm with a bearing and cable attachment to vary the stiffness of the bar as you drive.
Good luck
Phil

[Ant]

Hello Paul,

This thread has got me looking. so far the best i can find in terms of a straight splined ant-roll bar is from a Peugeot 106 and that was on Ebay, i haven't been able to find a proper supplier of universal antiroll bars but where theres a will theres EBAY!!!! I think the 205 may have had these type too.

Keep us up to date with your decisions etc so others may follow

[Paul W]

Thanks for all the info guys, I'll give the stainless a miss for the moment as it doesn't seem the best way to go. I'll post if I find anything that i can use.

[Ant]

Just found that Rally Design do a sierra anti roll bar kit. its a rod with ends type, only 95quid. gonna call them monday to see about lengths. the rod isn't splined just has a hole through the tube so the arms could be easily fabricated i think to make it fit our application

[Jim c]

Paul


Dont even bother jerking around trying to make it look for it.
Something close but not quite is always a pain in the arse as far as I am concerned
Get copper pipe in a similar size bend it to the shape that you want.
1/2 hour to make a pattern its all over.
Give it to a sway bar manufacturer as a pattern and Shazzam its done.

All you will have to make is the drop links.

[egoman]

If you are looking for splined bars that wont break you go to the oval track supply houses. The sprint cars and midgets use the torsion bars for suspension and they are available in many lengths and rates. They are also available as hollow bars for the weight conscious. Google Afco or Sanders and see what you come up with. Good luck.

[Ant]

The rally design kit just arrived, first look seems promising. just have to cut arms down to fit the front and the rear looks the same. Probably easiest to fabricate drop links than find ones of the right length.