If you make a sliding block type follower, the clearance issue becomes self correcting in that the tube is fully supported ahead of, and to the point of tangency with the die. If you trig out the distances and angles, it becomes obvious real fast that a few thousandths of clearance can produce a significant offset between the two tangent points. Or a heavier wall tube will produce a bend that has a 'jog' at the end of the bend where it looks like the bend has been made to some angle and there's a slight reverse bend at the roller contact point which reduces the total bend angle somewhat. A thin wall tube can distort noticably due to lack of support. When the roller is moving ahead of the tube's tangent point with the die, two things can happen. With a plywood form, the elastic deformation of the wood itself will create clearance in addition to any built in clearance at the pivot points, etc. As Rex said, it'll work as long as the points of tangency on the die and roller are coincident, but that's much easier said than done unless everything is built to high standards of accuracy. That said, your most likely souce of problems will be the roller type follwer. Bending on a 12' + radius won't require sand packing or any other sort of similar measures. In these situations, locating a bender/roller with the prior experience in handling these tough and tight bending jobs can be very helpful.You can bend unsupported 1 1/4' x 16ga wall tube on a 5' clr with negligible distortion. Available tooling, tube size, material thickness and composition are all components that can add into what the minimum bend radius is for a piece of metal. 8Г—4 Aluminum Tube Cracking 8Г—4 Stress-Relieved Aluminum TubeДЄs you can see, determining the minimum bend radius for a piece has many factors to take into account. In the end, this caused a much improved final product for the customer with no additional material cracking issues. To solve the issue, the material was sent out to be stress-relieved before rolling was continued. However, the aluminum tubing began to crack, possibly due to age-hardening coupled with the tight radius. The same tubing rolled in carbon steel could be pulled much tighter. One previous job which provides a good example of this used some 8 x 4 aluminum tubing rolled the hardway to a 16 foot radius. Material used can also change the minimum bend radius. Increasing the wall thickness on a tight radius bend generally improves the final quality of a rolled tube as well as lowers the minimum radius a piece can be rolled with minimal distortion issues. Another important factor to consider when looking at pipe or tubing is the wall thickness of the piece to be bent. In these cases, the minimum radius will likely need to increase beyond a 3D size. While it may not be a minimum for every bender, a 3D bend radius is a commonly used starting point for minimum radius bends.ДЄs a piece size gets larger, pre-made tooling for tight bends will be less common. For tight rotary draw bending, maintaining a bend radius that is a whole number multiple may increase the capability of the steel bender to meet your needs. So, even though it may be possible to give a piece a 2D or 3D bend, a 3.5D bend may be more difficult because the tooling is not on hand. This type of bending is usually performed on a rotary draw bender for speed and precision, which requires specific tooling built for each bend. 2D = 4 inches, 3D = 6 inches, and 5D = 10 inches for a 2 inch diameter pipe. In these cases, the 2D would reference a centerline bend radius of two times the diameter. For example, on a 2 inch pipe elbow, common bend measurements may be referred to as 2D, 3D, or 5D. In some instances, a rough guide for minimum radius bending would be to use a multiple of the piece diameter. A 2вЂќ carbon steel pipe will have a different minimum radius from a thin wall 2вЂќ aluminum tube. There are many factors to take into account when determining the minimum radius such as the material composition, shape, and size. In some instances, an estimator can quickly say yes or no based on prior knowledge and bending experience. Often, in the rolling and bending industry, we field requests asking about the minimum radius to which we can roll or bend a piece.

Tube bending radius