How to Bend Tubing
Metal fabrication tips and tricks
Structural steel tube is a great compromise of strength and weight. Tube is built to be used in structural applications and to contain pressure. Pipe is built to transport fluids and gases. We don't want to use pipe unless we are building plumbing or exhaust on our 4x4s. We want to use structural tubing for 4x4 hard parts. Welded seam, Drawn Over Mandrel (DOM), and Chromoly tube are all great ways to make bumpers, rollcages, shock hoops, frame crossmembers, roof racks, tire carriers, and more. By adding bends to said tubing, it becomes much more versatile. Hell, you can build a whole 4x4 rig out of tube if you know what you are doing.
Still, most, if not all of us weren't born skilled metal fabricators. We have to learn. Well, have no fear, you've come to the right place to learn some of the basics of structural steel fabrication. In this article we are going to show you how to make your first bend. This does require the use of relatively expensive specialty equipment known as a tubing bender. Each type of bender is slightly different, and you will have to refer to your bender's owner's manual on how to use each individual one, but all will use the same basic premise and are subject to the same laws of physics.
Tubing Bender Anatomy
Tubing benders all have similar anatomy, and most commercially available tubing benders follow a similar pattern of parts unless you have a really fancy bender. Most benders we've used have a bending die, follower die, U-strap or holding die, a fixed arm, and pivoting arm, pins, mount, and some sort of ratcheting mechanism. Some benders also have added on degree rings, and hydraulic or air over hydraulic rams to actuate the bender. As said, each bender will be slightly different, but the basic idea is that straight tubing is forced into the bending die using the follower die while being held in place by the holding die or U-strap. The pivoting arm moves the dies relative to each other, allowing you to add 1 degree up to about 180 degrees of bend (if you have a die capable of bending that far). Please note that there is a difference between a tubing bender and a pipe bender. Pipe benders do not retain the structural properties of tubular steel as well as a true tubing bender and tend to kink tubing or pipe, forming a weak point.
Steel Spring Back
Steel, like most metals, is malleable, but it also has a memory. That means it will return to its previous shape, a phenomenon known as spring back. So when adding a bend to steel tubing, you can deal with this by bending the steel just beyond where you want it to remain. For example, if you want a bend that is 25 degrees you have to bend the tubing to about 27 or 28 degrees. The tube will then spring back to the desired 25 degrees. The amount of spring back you'll have depends on the size of the bend, but it's generally around 3 percent.
Make an Example Bend
One more thing you'll have to do to make repeatable bends is mark your die and your tubing to consistently place your bends. What most folks do is establish where the forming die hits the tubing. This is the spot where your bend will start in the tubing. You can use a paint pen to mark the location on your die and use your handy sharpie to mark your example bend, which you will use as a tool. Now you can bend your example bend to 45 degrees, or 90, whatever works for you. With the point where your bend starts you can hold the example bend up next to your work to determine where to put your bends.
Simple Angle Finder Tool
Now, to figure out what angle you need to bend, you can completely nerd out on angles, measurements, math, and geometry, or you can make a simple settable angle finder out of two pieces of flat bar and a bolt with a locking washer. Use the tool to figure out how much bend your piece of tubing needs, set it, and compare to the tubing while in the bender.
You Can't Unbend Tubing
Sadly, if you mess up and overbend a piece of tubing, generally you've just created scrap and you have to start your part over again. Having said that, we have successfully un-bent tubing a few degrees (like 1 to 2 degrees) with brute force. To do this, try inserting the tube into an open frame rail or receiver hitch and reef down on it. But be careful because it's easy to slip and fall, hurting yourself or damaging your rig.
Different Dies Yield Different Bends
As we hinted at earlier, there are a couple different kinds of die sets available for tubing benders. The main differences we would point out are: 1) Different dies are available to bend different shaped materials. You want to pay attention to using the right die for the right material. There are dies for round tubing, square tubing, and round pipe (outside dimensions of pipe and tube are different). You can't bend your material without the correct die. 2) Different dies can follow different bend radiuses. That means the smaller the bend radius, the sharper the turn of the bend. A 5.5-inch radius means that if the die could make a full circle, the radius of the circle would be 5.5 inches. You can have two dies for the same materials that have different bend radiuses. This can be helpful when bending tight interior rollcages, or matching tubing to the radius of a body panel on a bumper. 3) Generally tubing bender dies are available as 90 degree dies or 180 degree dies. The 90 degree dies can only bend up to 90 degrees. We prefer the 180 degree dies because they can bend under 90 and up to 180 degrees. Just don't bend past that, or you may get your die stuck in some tubing.
Sadly, you just can't bend pieces of tubing that are too short. That means that those little 1-foot sections you've collected won't fit into the bender and thus can't be bent. This also means that if you want bends tight to the ends of tubing, you will have to make your bend and then trim down the tubing, forming the bend. This causes everyone, even great fabricators, to waste materials. It's just part of the deal. You can't make nice metal fabricated parts without wasting expensive tubing, but making mistakes is the fastest way to waste time and money.
Multiple Bends in One Piece of Tubing
Adding multiple bends to one piece of tubing has to be done very carefully. It's very easy to get two bends out of plane with one another, which means your part won't be flat. Also, if you need to clock one bend relative to another bend, you will need to make some sort of semi-permanent reference mark to your tubing so you can make one bend, rotate the material relative to the bender's die a fixed amount, and make another bend. There are tools to help with this available in the aftermarket including digital levels and angle finders. A cheap option is to tack weld a flat piece of steel to the tubing before your first bend. Set the flat steel parallel to the benders forming die before your first bend using a digital level or angle finder (PS, your smart phone probably has a digital level). Then for your second bend you can either set the plate equal to the die again or add rotation to make a controlled out of plane bend.