- JD2 Model 3 Tube Bender
- Angle finder (measures orientation of object relative to gravity)
- Protractor or angle measure
It is important to place the bend in the accurate position on the member, in the correct bend plane, and bent to the correct angle. The most difficult tube to fabricate is a 2+ bend member with each bend forming a different plane of bend. Minimize the use of multi-bend members if at all possible during the CAD stages of frame design. This will help reduce the time it takes to build your car and should improve the accuracy of the tubes and nodes on the frame.
Positioning the Bend
You will have to know the characteristics of your bending dies to determine how to accurately load the tube in the bender to place the start of the bend exactly where you want it. It is best to scribe a witness mark on the bending die or use a flat edge on the die with a known offset that you can use to reliably get the bend you desire. See the link below for Template Bending according to the manufacturers of the JD2 bender.
Accurate Bend Angles
You can always reload a tube and bend it further, but it is nearly impossible to unbend a tube once it is bent too far (more than a degree or so). It is best to bend the tube just short of your target angle, remove it from the bender to let it unspring, measure the angle with a protractor or angle measure, then bend it a little further. Once you are familiar with the tube bender and the material properties of the steel you are using, you can quantify this springback and remove most of the guess and check of this process to more quickly get your desired final angle.
Accurate Plane of Bends
If you are placing multiple bends in the same tube or are orienting the tube notches with respect to the bend plane, you must know that everything is in the correct orientation. Use an angle finder clamped onto the tube to either accurately rotate the tube between bends or to keep the bends in the same plane for a tube that should make only one plane (e.g. the RRH).
Unless you have CNC tube bending equipment and software, the answer to accurate bends is the Template Bending technique. JD2 has published a great set of instructions explaining how to do Template Bending:
The JD2 bender leaves the tube with a reduced cross section where it is bent due to the elongation of the metal around the radius. If the radius is too tight or the tube wall is too thin the tube will buckle or crinkle, usually on the inside of the bend. Technical Inspectors will not allow you to use a buckled tube in a structural member of the car. Usually the JD2 bender has the following limitations:
(need a table of bend radius, tube diameter, and wall thickness here)
There are two ways to address the tube buckling, and each is fundamentally just a method to support the inside of the tube from buckling. The first is Mandrel Bending, and the second is Compacted Sand. Mandrel Bending frequently is used for engine air intake and exhaust plumbing where it is important to maintain the cross section for free flow of air. The Mandrel Bending equipment is very specialized and expensive, and that likely limits an SAE team to getting Mandrel Bends sponsored by a fabrication company or the team would use the Compacted Sand technique.
- Roll Bending: For very large radius bends you can use a roll bender. This technique is excellent for making sweeping curves in FBM and rear bracing members seen on some teams' cars.