A relatively simple, manually operated tool enables precise bending (typically, within ±1/2° of the specified bend angle) of a metal tube located in a confined space, with a minimum of flattening of the tube and without significant gouging of the tube surface. The tool is designed for use in a situation in which the tube cannot be removed from the confined space for placement in a conventional bench- mounted tube bender. The tool is also designed for use in a situation in which previously available hand-held tube benders do not afford the required precision, do not support the tube wall sufficiently to prevent flattening or gouging, and/or do not fit within the confined space.
The tool is designed and fabricated for the specific outer diameter and bend radius of the tube to be bent. The tool (see figure) includes a clamping/radius block and a top clamping block that contain mating straight channels of semicircular cross section that fit snugly around the tube. The mating portions of the clamping/ radius block and the top clamping block are clamped around a length of the tube that is adjacent to the bend and that is intended to remain straight. The clamping/radius block is so named because beyond the straight clamping section, its semicircular channel extends to a non-clamping section that is curved at the specified bend radius. A pivot hole is located in the clamping/radius block at the center of the bend circle.
The tool includes a bending block that, like the other blocks, contains a straight semicircular channel that fits around the outside of the tube. The bending block contains a pivot hole to be aligned with the pivot hole in the clamping/radius block. Once the tube has been clamped between the clamping/radius and top clamping blocks, the bending block is placed around the tube, the pivot holes are aligned, and a pivot pin is inserted through the pivot holes.
To bend the tube, the bending block is pivoted so that its semicircular groove slides along the tube, forcing the tube into the curved portion of the groove in the clamping/radius block. An arm that extends from the clamping/radius block and a similar arm that extends from the bending block provide mechanical advantage for generating bending torques and forces. These arms are actuated by turning a nut on a threaded rod that runs through holes in both arms.
To ensure a precise bend, one should measure the bend angle by use of a protractor at intervals during the bending operation. Even so, it is desirable to calibrate the tool in two ways: (1) measuring and/or calculating the increase in the bend angle for each turn of the nut and (2) measuring and/or calculating the amount of springback. Calibration should facilitate the approach to the final stage of bending (with a slight over-bend to allow for springback) with greater assurance that at the end, the tube will be bent to the desired angle within ±1/2°.
This work was done by Gary T. Davis of Goddard Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category. GSC-14412.