Rotary Draw Bending

Rotary draw bending forms precise, repeatable tube and pipe bends with controlled radii and angles, ideal for tight-radius, appearance-critical parts.

Overview

Rotary draw bending (RDB) uses a rotating bend die and clamp die to pull tube or pipe around a fixed radius, producing accurate, repeatable bends with good surface finish. The process excels at tight and consistent centerline radii, controlled bend angles, and maintaining alignment between multiple bends in the same part. It’s commonly used with or without internal support tooling (mandrels, wipers) depending on wall thickness and bend severity.

You should consider rotary draw bending for structural or cosmetic tube parts where bend location, angle, and radius consistency matter, and production ranges from prototypes to medium volumes. It handles a wide range of diameters and wall thicknesses but is limited by machine capacity and required clamp lengths before and after bends. Expect good control over ovality and minimal wrinkling on moderate bends; very thin-wall or extreme tight-radius work may require upgraded tooling or a dedicated mandrel setup, which increases cost but improves quality on demanding geometries.

Common Materials

  • Aluminum 6061
  • Stainless steel 304
  • Mild steel (1018/1020)
  • Chromoly 4130
  • Titanium Grade 2
  • Copper tube

Tolerances

±0.5° on bend angle, ±0.010–0.030" on critical bend locations with proper fixturing

Applications

  • Roll cages and chassis rails
  • Automotive and motorcycle handlebars
  • Exhaust headers and tailpipes
  • Hydraulic and fuel lines
  • Furniture and display frames
  • Medical equipment frames and rails

When to Choose Rotary Draw Bending

Choose rotary draw bending when you need accurate, repeatable tube or pipe bends with a defined centerline radius and good surface finish. It fits low to medium production volumes, multi-bend parts, and applications where bend-to-bend alignment and aesthetics are critical. Best suited to moderate to tight radii within the machine’s diameter and wall-thickness limits.

vs Mandrel Bending

Pick rotary draw bending without a full mandrel setup when walls are not extremely thin and some ovality is acceptable, which keeps tooling and setup costs lower. Mandrel bending is better only when you must tightly control ovality and wrinkling on very thin-wall or severe-radius bends, or need near-perfect roundness through the bend for flow or fitup.

vs Compression Bending

Choose rotary draw bending when you need better control over bend radius, angle, and tube shape, especially on tight radii or multi-bend parts. Compression bending suits simple, large-radius bends where appearance and dimensional accuracy are less critical, while rotary draw bending delivers higher precision and repeatability.

vs Roll Bending

Use rotary draw bending for shorter parts with defined radii and precise bend locations, such as frames, rails, and headers. Roll bending makes sense for large sweeping curves, big radii, or long coils; rotary draw bending is more efficient and accurate for discrete, tighter bends with controlled centerline radius.

vs CNC Tube Bending

Select conventional rotary draw bending for simpler bend programs, lower part counts, or when you can accept manual setup and adjustment to reduce cost. CNC tube bending (often using rotary draw hardware) becomes preferable when you have complex multi-plane bends, tight positional tolerances, and higher volumes that justify automated control and faster changeovers.

vs Stretch Forming

Choose rotary draw bending when you need localized bends with standard tube tooling and do not need to stretch-form long contoured shapes. Stretch forming is better reserved for large, smooth, compound curves in aerospace and architectural parts, while rotary draw bending efficiently produces discrete, repeatable bends at specific locations.

Design Considerations

  • Keep bend radius at or above 1.5× tube OD for standard tooling; tighter radii may require special tooling and higher cost
  • Provide minimum straight lengths before and after bends (typically 2–3× OD) for clamping; very short tangents can be unmanufacturable or require custom fixtures
  • Specify allowable ovality and wall thinning clearly; overly tight requirements drive the need for mandrels, wipers, and more expensive setups
  • Dimension from functional datums and bend centerlines rather than from tube ends to reduce stack-up and improve repeatability
  • Avoid placing holes, slots, or weld seams directly in the high-strain bend region unless you validate formability with samples
  • Provide a 3D model or at least a developed tube centerline with bend angles, rotations, and radii to help the shop program and fixture the part accurately