There have been a number of post flying around about cages - buy a replacement, reinforce the stock, etc, etc. I thought it might be good to put together a "cage tech" thread that would address the basics, and more, of cages for those looking to upgrade in some way. (Mod's maybe this could become a Sticky.)
Materials
Chrome Moly (CM)
Pro's: Higher tensile strength allows the use of thinner walled tubing to achieve roughly the same amount of strength as mild steel (Tensile strength around 90,000 - 100,000 psi, before heat treating)
Con's: More brittle than mild steel; more prone to breaking, rather than bending, particularly at welds if the weld is not properly normalized; more expensive to purchase and work with than mild steel
Mild Steel (DOM or HREW)
Pro's: Relatively less expensive than CM; will bend more before breaking vs. CM; easier to work with - no special normalization process required
Con's: Lower tensile strength requires thicker walled tubing to achive roughly the same amount of strength as CM - this equates to more weight
What is DOM? Drawn Over Mandrel tubing is formed from strips and electric-resistance welded, then cold drawn to size. The cold drawing process causes the weld line to virtually disappear and gives the tubing its strength by cold working and allows more consistent dimensions and tolerance than HREW. (Tensile strength around 80,000-85,000 psi) DOM is slightly more expensive than HREW and less expensive than CM.
What is HREW or ERW? Hot Rolled Electrical Weld tubing is formed from hot rolled strips and electric-resistance welded to form the tubes. Evidence of the weld is typically visible inside the tubing. (Tensile strength around 45,000 psi)
Design
The most common phrase you will hear in roll cage design is "
triangulation." Triangulation, in its most basic form, means dividing a square section of cage into triangles to make it stronger.
Below is an excellent example of triangulation.
A second, and equally important, element of design is that of
intersection points (sometimes called
nodes). The basic theory is this - at any point where one piece of tube intersects with another, there should be a third piece of tube on the opposite side of the intersected tube to carry the load.
Below is a good example of intersection points or nodes (where the tubes forming the X carry through their intersection with the hoop to another tube running in roughly the same direction).
A third basic tenet is to
avoid unnecessary bends. While form-following bends can look cool a bent tube is a tube looking for an excuse to bend further.
The B and C pillar bends in this cage, without additional reinforcement, are just waiting to bend the rest of the way on impact.
Gussets are another design element that can help prevent bent areas from bending further. Gussets can be an additional piece of tubing, creating a triangle (see triangulation, above) or a piece of flat steel as seen below.
Flat steel gusset.
Here is an example of good use of a tube gusset (in the corner of the A pillar and roof).
Construction
The third leg of the conceptual triangle (pardon the pun) of a quality roll cage is the construction of the cage. Many people focus on the quality of the welds. This is certainly of the utmost important, but it can be difficult to see if the cage has already been painted or powder coated. Big, ugly booger welds will be obvious, but it will be difficult to tell how well the welds have penetrated the steel.
Fit and finish is also important. How well were the tubes notched to fit together? Are all the angles equal and opposite? Are parallel pieces bent at exactly the same angle. Most of this is also difficult to tell - particularly if you are buying online.
Hopefully, many of you will find this information helpful and others, with cage-building experience, will add to the information and create a valuable resource for RZR Forums readers.
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