Tube Bender tech

Welcome to the bender tech page. We provide you with the most reliable information available on bending tube, chosing materials, picking out die sizes, and understanding the engineering behind tube bending and chassis fabrication and safety. Feel free to link to this page as a technical resource. We will not change the web address. Do not copy and paste the info or pictures from this site without permission or a proper citation of the source with a link, this content is copyrighted.

Hydraulic Tube Bender

Tubing Bender Overview

The Rogue Alpha Tubing Bender is an affordable solution to bending tube without mounting the bender to the ground, buying adapter kits for hydraulic cylinders, or requiring you to rip on a 4 foot bar while you try to read a degree wheel you can't even reach. Our kit comes with EVERYTHING you need except the hydraulic cylinder, which is available nearly everywhere (without paying shipping). Our Rogue Alpha Bender bends vertically to save space in your shop. It doesn't need to be mounted to the ground, making it portable. It can be operated by hand (hydraulically), or by power (air compressor). This tool is Made in the U.S.A. This tool ships as a weld-together kit.

What is Included:
*1 Die set of your choice (all 180+ degree) 3.5" to 6" CLR
*Degree wheel/pointer
*Printed instructions

What you need:
*Welder to assemble base (about 2 hours for assembly)
*$72 HF Air/Hydro Cylinder PN 94562($90 w/o coupon)

Link to HF ram

Bender Operation

1. insert tube in machine, tighten bolts to clamp tube. Hook up machine to compressed air source.
2. Open valve (like flipping a switch).
3. Machine bends tube up to 96 degrees, at which point you close the valve to stop.
4. remove pin from ram end, allow springs to return ram to closed position, and re-insert pin in next hole for the ram.
5. Go back to step 2 (using the next holes) to bend to 145 degrees. A third cycle will take you beyond 180 degrees.

We have had many customers learn how to bend tube on our bender by themselves with no prior bending experience. Our goal for the Alpha Tubing Bender was to make fabrication more affordable, and also have a simple to use machine that won't hold back advanced fabricators. Our customers agree that we have met these goals!

About the Video:

This video shows how to make a 90 degree bend on our old bender (the new one does 90 degrees without changing pins). The tube is a little deformed because we're bending 1.75x.120 on a very tight radius (4.5"). We also offer a 6.0" CLR die set that bends this material much better, but it costs more. Also please note that we ran the air pump for the ram off of our compressor tank only, so the tool slows down considerably as the pressure drops. We didn't want to have our compressor kick on mid-video. Enjoy!

Bender Capacity

The imaage below shows 3 wall thicknesses of 1.75 1020 DOM steel tube: .120", .188", and .250". Bending 1.75x.250 requires our "HD Kit", which you can find on our Die Sets web page. Our bender can bend from 1/2" to 2" round tube and from 1/2" to 1.25" square tubing. We have successfully bend up to .156" thick DOM tube in 2" diameter. That is currently the maximum rated capacity of the machine, but we are still testing thicker material!

Hydraulic Tube Bender

Tube? Pipe? Huh?

You may have noticed we have tube and pipe dies. Tube and pipe are not the same. Here are the basic differences:

PIPE is a vessel, intended to carry fluids like natural gas or water. They are rated for pressure, not strength. Pipe measurements are based on the inside diameter (ID), not the outside diameter (OD). The pipe measurement schedule has evolved and sizes no longer match ID or OD. For any pipe size, you must look up the diameters on a pipe schedule to find out the OD and ID. For any nominal pipe size, the OD will be constant when you change wall thickness. So a 1.25" schedule 40 pipe is 1.660" OD with a .140" wall. A 1.25" schedule 80 pipe is 1.660" OD with a .191" wall. Pipe is generally less expensive and weaker than tube of a similar size.

TUBE is a structural member and it is rated for strength. They are sized based on OD, and they are consistent. A "1.5 .120 wall tube" is actually 1.500" OD and has a wall thickness of .120". Tube is more expensive than pipe and has significantly better material properties. We recommend tube for all applications, but understand that sometimes pipe is convenient, functional, and safe. That is why we make dies for both!

What is CLR?

CLR stands for Center Line Radius. It is the industry accepted method for measuring the size of a bend. An example of a small CLR is pipe fittings for plumbing. A large CLR example is the large hoop that makes the outside of a trampoline frame. CLR is measured from the center of a bend to the center of the tube or pipe being bent. Look at the image below for claification. The 4.625 measurement is the inside radius, and the 6.375 is the nominal outside radius. You can see that the outside radius is actually outside the tube in this drawing. The outside of the tube will naturally pull inward a slight amount from the tension caused by bending without a mandrel inside the tube.

DOM Die Set CLR explained

Tube Tech

Tube Collapse and FEA analysis
By Rogue Fabrication, LLC,

This question has been asked a few times: “Does 1.75x.120 collapse at all when bent on a 4.5 inch radius?” The short answer is yes. All tube collapses (pulls in the outside of the bend) to some degree on EVERY bender. Even with mandrels you will have SOME collapsing.

This answer leads to two more questions: How much does the tube collapse or pull in? What is the effect on strength? The short answer: it will collapse 4-10% on a 90+ degree bend, and there will not be any notable effect on strength.
Read on to see how we came to these conclusions…

Part 1:How much does the tube collapse?

A 90 degree bend in 1020 DOM steel tube (1.75x.120) bent on a 4.5” CLR die loses about 10% of its axial cross section diameter (figure 1). If we consider this to be the “height” of the tube, then its “width” gains a couple percent. DOM steel doesn’t like to stretch, so this is the only place for the material to go when it doesn’t want to get thinner. Similarly, the same material bent to 90 degrees on a 5.5” centerline loses about 5% of its axial cross section diameter (figure 2). The “width” again increases by about a percent. These are actual measurements taken from tube bent on a 4.5” and 5.5” CLR die. These results aren’t surprising, we all know tube forms better at larger radii, but most of us aren’t going to roll bend an interior cage or a stinger, so we need to know if this has any effect on strength.

Hydraulic Tube Bender

Hydraulic Tube Bender

Part 2: Does it matter for strength?

There are two ways to figure this out: roll a truck with a cage built from each bend radius and accept all the variability in your testing… Or use finite element analysis to simulate loading and calculate stress. We chose to use FEA. We modeled two bent tubes, both spanning 10.375” in height and 21.75” in length. Both tubes were modeled with true “collapsed” geometry, using the physical measurements taken from actual bent tube. Both tubes were loaded the same, 6500 pounds applied to quarter sized areas. We ran the test on the bend and on the straight part of each tube. In this test, both ends of the tube are assumed to be completely welded to another fixed member. This load is a static load, and is comparable to balancing a very heavy fully loaded rig on a small rock that doesn’t crumble.

Brief Glossary:
• Yield: Refers to yield strength, the stress level where a material will bend and not bend back. In the SolidWorks 2012 materials database, this property is 51 Ksi for 1020 steel. It may be different depending on material source and processing.
• Tensile strength: Refers to ultimate strength, the stress level where a material will deform undesirably beyond typical yield. In the SolidWorks 2012 materials database, this property is 61 Ksi for 1020 steel. It may be different depending on material source and processing.
• DOM: Drawn over mandrel. Non welded tube, typically stronger than HREW tube, and usually 1020 or similar steel.
• Ksi: Kilipound per square inch. That right, scientists blended imperial and metric. 1000PSI = 1KSI.

Test 1: 4.5” CLR bend, 1.75x.120 1020 DOM, load on the outside of the bend.

The arrow on the stress scale indicates where the yield is for the material (point when the material bends and doesn’t come back). Anything in the red indicates material failure. Assuming the rock actually stays intact, it looks like the rock would dent the tube in the green area, and possibly cause a small fracture where the red is in the center (about the size of a dime). In reality the load would spread out as the dent formed or as rocks/dirt/sand/etc moved, and the outcome would be a small/shallow dent and nothing more. The top of the stress scale shows the max being 89.8 Ksi, but as stated, this local result (the red spot) is not representative of a real life situation. This stress also exceeds the tensile strength of 1020 steel, making the max even less relevant to this study. What is significant here is that the tube doesn’t bend. See figure 3.

Hydraulic Tube Bender

Test 2: 4.5” CLR bend, 1.75x.120 1020 DOM, load on the straight portion.

This test shows more stress in more areas. We have yielding near the welded joint on the right, and a larger dent likely to form in the tube where the load is applied. If there was movement involved, this would probably bend the tube in the straight section right where the load is. The stress in the bend area is significant, although the material isn’t close to yielding in that area. This time the top of the stress scale shows the max being 131.4 Ksi, but again, this local result (the red spot) is not representative of a real life situation unless your rig fell off a lift onto a piece of hardened tool steel fastened to your shop floor without touching anything else. See figure 4.

Hydraulic Tube Bender

Test 3: 5.5” CLR bend, 1.75x.120 1020 DOM, load on the outside of the bend.

This result is essentially the same as test 1. The red area appears larger and the max stress is 9.8 Ksi lower, but since these are both in the area where the load would spread out, they are not significant differences. See figure 5.

Hydraulic Tube Bender

Test 4: 5.5” CLR bend, 1.75x.120 1020 DOM, load on the straight portion.

This result is essentially the same as test 2. The max stress is 6.3 Ksi lower, but since these are both in the area where the load would spread out, we can disregard it. If there was movement involved, this would probably bend the tube in the straight section right where the load is, just like in test 2. See figure 6.

Hydraulic Tube Bender

To summarize the test, both bend radii produce structures of similar strength when using the same material. The difference in “collapse” between the two is notable at 5%. Most people can see that a tube is flattening to some degree when the collapse percentage is at or above 3-5%, so most people will be able to see the collapse on tube bent on either radius if they are specifically looking for it. When shopping around for a bender and dies, this is something to take into consideration. Smaller dies fit bodies and interior cages better, but they make it easier to spot the inevitable deformation that tube bending produces. Tighter bends will allow for narrower shock hoops, more headroom with an in-cab cage installed, and better looking wrap-around bumpers that require less body cutting.