Rotary Draw Bending

Rotary draw bending forms tubes around a radius die with a clamp and pressure die, producing tight-radius, repeatable bends with controlled ovality.

Overview

Rotary draw bending (RDB) pulls a tube around a fixed bend die while the tube is clamped and supported by a pressure die; a wiper die and (optionally) internal mandrel control wrinkling and flattening. It’s the go-to method for accurate bend angles, tight centerline radii, and consistent part-to-part geometry.

Choose RDB for production tube parts where fit-up matters: multiple bends, close tolerances, and defined bend locations. It handles round and many shaped tubes, and works well for steel, stainless, and aluminum.

Tradeoffs: dedicated tooling per tube OD and bend radius drives setup cost and lead time. Tight radii increase risk of ovality, wall thinning, and surface marring, especially without a mandrel/wiper. Very large radii, gentle sweeps, or long arcs are often inefficient, and bend feasibility depends heavily on tube condition, weld seam, lubrication, and straight length requirements for gripping.

Common Materials

  • Mild steel (A513)
  • Stainless steel 304
  • Stainless steel 316
  • Aluminum 6061
  • Copper
  • Titanium Grade 2

Tolerances

±0.5° bend angle; ±0.020 in bend location (typical, depends on tube size and setup)

Applications

  • Automotive roll cage and chassis tubes
  • Hydraulic hard lines and coolant tubes
  • Handrails and guardrails with tight elbows
  • Bicycle and motorcycle frames
  • HVAC and refrigeration copper line sets
  • Aircraft fluid and instrument tubing

When to Choose Rotary Draw Bending

RDB fits parts that need tight, repeatable bend radii and accurate bend angles, especially with multiple bends on one tube. It’s a strong choice for low-to-high volumes when tooling cost is justified by consistency and reduced rework. It works best when you can standardize tube OD, radius, and bend program across a family of parts.

vs Mandrel Bending

Choose rotary draw bending when you need accurate bend geometry but the application can tolerate some ovality and wall thinning, or when radii are not extremely tight. RDB without a mandrel reduces tooling complexity and cost versus full mandrel setups while keeping good repeatability.

vs Compression Bending

Choose rotary draw bending for tighter bend radii, better control of bend location, and improved repeatability across production runs. RDB is typically preferred when cosmetic quality and dimensional control matter more than minimal tooling cost.

vs Roll Bending

Choose rotary draw bending when you need discrete bends with defined angles and short tangent-to-tangent distances. RDB holds tighter control on bend start/finish and angle than roll bending, which is better suited to large-radius sweeps and continuous curves.

vs CNC Tube Bending

Choose rotary draw bending when the part requires the rotary draw tooling stack (bend die/clamp/pressure/wiper/mandrel) to meet radius, ovality, and wrinkle limits. CNC is often the machine/control platform; RDB defines the bend method that delivers tight-radius, high-repeatability results.

vs Stretch Forming

Choose rotary draw bending when you need compact bend radii and sharp transitions between straight sections and bends. Stretch forming favors large, smooth radii and can struggle to hit the same tight CLR and bend definition as RDB on small tubes.

Design Considerations

  • Call out tube OD, wall, material/temper, and weld seam orientation; these drive feasible radius and ovality control
  • Specify centerline radius (CLR) and bend angle per bend; avoid relying on implied radii from CAD splines
  • Provide sufficient straight tangents for clamping and tool clearance; short tangents increase scrap and secondary ops
  • Limit ultra-tight CLR-to-OD ratios unless you plan for mandrel/wiper tooling and accept thinning/marking risk
  • Define acceptable ovality, wall thinning, and surface finish in bend zones; otherwise shops will quote conservatively
  • Avoid stacking bends too close together in different planes without checking interference with dies, mandrel rod, and collet/gripper length