Author: Jordan Powell Photos: Jordan Powell
After three installments of Fab 101, we’re finally jumping into the deep end and going to start bending up some tubes. Tube bending can seem like an intimidating task, and we don’t blame you because, let’s be honest, a tube bender looks like some sort of medieval torture device. However, if you want to become a successful fabricator, you need to know how to use this machine correctly, which is why we enlisted the help of the Fab School’s own Troy Johnson. Before you flick the machine on and start going crazy with some tubes, you need to have in mind what you’re going to build, and what your design is going to look like. If you remember last month’s article, you’ll understand what Troy refers to as “know your knowns,” and most likely use his key phrase for every project you jump into. For this project, we will be building the main hoop for a roll cage, with the “known” being the cab of a truck. Though this might seem like a daunting task, it’s very simplistic in design, consisting of only a few small bends. So grab your personal floatation device and get ready to paddle as we dive into another section of Fab 101.
What you’ll need: To start things off, you’ll need a degree in calculus and a fancy CAD program. We are kidding, of course! When you jump into tube bending, there are some basic tools you need to get your hands on: an automatic center punch, scriber, sliding T-bevel, protractor, stainless steel ruler, measuring tape and what Troy likes to call a “half shell,” which is a half piece of tubing that serves as a guide when you’re scribing a line on a piece of tubing. Although it’s not pictured here, a silver welder’s pencil is useful when trying to make a visible, erasable mark on metal.
The Bender: Tube benders come in a variety of shapes and sizes, but the JMR electric bender is the weapon of choice at the Fab School. If you are just starting out and don’t have lots of cash, or are making just a few bends, you may want to look into a manual bender—one that can be later upgraded to hydraulic is also a good option.
Not All Dies Are Equal: Before you operate your tube bender, become familiar with your die, and where it starts a bend. Some dies have visible marks that show the operator where a bend will start and some don’t. It may seem obvious, but also make sure to use the proper die for the diameter of the tube you are using.
Make Your Template: When it comes to creating a roll cage, or any other tubular design, you can either use a simple 90-degree tubing template, or some complex trigonometry. We’ll go the easy route. In order to do this, you’ll need a 20-inch long piece of tubing that’s the same diameter as your roll cage. Next, measure about six inches in and mark a line. This will serve as your start point for your bend. Once that’s all done, load it up into your bender, and crank that thing to 90 degrees. Depending on the wall thickness or the OD (outside diameter) of your tubing, there will be some spring back, so it’s important to check your bend (pictured here) before you call it done. If you find that you went a little too far on your bend, don’t worry. Since cold worked steel has something called memory, you can throw your piece into a vise and bend it back.
Mark The Bend Points: Once you’ve bent up your 90-degree masterpiece, you now have to mark where the start point of the bend is on your template. This is an important step, as it will allow you to determine where to start bending on the actual tubing you will be using. There are two ways to do this: you can visibly see and feel where the bender worked its magic because there will be small indentations in the tubing, or you can grab an object that has a flat edge, and slide it up on the tubing until you see an air gap (pictured here). After that point is marked, your template is now complete.
Getting Your Measurements: There shouldn’t be any guesswork when bending up some tubes for a roll cage. That being said, you again need to figure out your “knowns,” and start making some measurements. So, break out your tape measure and start figuring out some key points inside your cab like the height, length and width. Once that is done, Troy uses some string and tape to accurately find the angles of his bends.
Find The Bend Points: To figure out where your bends are going to start, you’re going to have to bring out that 90-degree template you made earlier. Place the straight section of your template on the piece of string that is taped up inside your cab, and slide it up the thread until the bend of your template makes contact with the cab. Now, using the marked points on your 90, envision where those lines would intersect your string, and draw a line to note where to start your bend on the full-size piece of tubing. Continue this process on every angle. By doing this, you will be able to measure where your bends will start and stop, which will help you figure out the length of tubing needed for your project.
Draw It Out: When the last two steps are complete, you can start drawing out a diagram. Since this roll cage design is rather large, the students at the Fab School drew up a half-scale model on some chipboard.
Alternative: An alternative method to the last three steps is to draw up a full-size diagram of your roll cage on a concrete floor.
Once your diagram is laid out on the floor, take your 90-degree template and place it inside the drawing. The point where the bend should start can be seen and is marked on the diagram.
The mark for the start of the bend is then transferred to the tube to be bent.
Keep It Level: To ensure that your roll cage stays level, bend after bend, Troy likes to use of a piece of angle iron to scribe a line all the way across his piece of tube. Once this step is complete, Troy will go back and transfer his measurements onto the piece of tubing, and then use his half shell to draw a line around the metal. This visible cross section will serve as a guide when you load your tubing into the bender, and help certify that your project stays level.
The Final Product: It’s finally time to bend up your work of art. One thing to remember when making your roll cage is to work from the center out, and hopefully it will look something like this when you’re all done. If not, practice makes perfect, so don’t give up!
Source: The Fab School (951) 782-0567 www.thefabschool.com