Occasionally, short distances between bends are unavoidable. Therefore conventional tooling with grip areas 3 and 4 times the tube outside diameter cannot be utilized. In this case compound tools or compound grip areas are necessary. A compound grip is essentially a grip or clamp area with a machined tube groove matching the contour of the previous bend. These grip sections are defined as either simple or complex depending on the specific plane rotation between bends. Simple compounds are the easiest to machine and therefore the least expensive. Simple compounds consist of plane of bend rotations equal to 0°, 90°, 180° or 270°. All other plane of bend rotations are considered to be complex and are more challenging to design and manufacture.
Sometimes conditions exist that necessitate the use of combination grips. This design of tooling allows for multiple positioning of the part within a given set-up. Often, combination grips are necessary with the use of CNC bending machines. Combination compound tools usually consist of a straight and simple or complex compound grip within a single tool. Serrations or a surface alloy treatment is often used in the primary and secondary straight sections of the combination grips to ensure a proper grip of the tubing.
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