proc_tube_butting

Tube Butting

formative · double-butted tubing, triple-butted tubing, internal cold-drawing

A steel tube is cold-worked so the wall is thicker at the ends — where stresses concentrate at welded joints — and thinner in the middle, where stress is lower. The reason a chromoly bicycle frame can be light without being weak. Specialty process; mostly seen in frame-builder supply.

Mandrel-controlled cold drawing varies wall thickness along the length of a tube. Single-, double-, and triple-butted profiles place material where shear and bending demand it (joint regions) and remove it from the middle. Standard product from Reynolds (UK), Columbus (Italy), True Temper, Tange.

Scale & Tolerance

  • scale (mm)100 – 2000
  • tolerance (mm)0.05
  • skillspecifier-level — frame builders pick a tube set; process is supplier-side
  • costmoderate to high per meter; high added value over plain tube

Equipment

  • school_shopno — purchased as finished tube
  • professionalspecialty mills (Reynolds 853, Columbus Spirit, True Temper OX-Platinum)
  • industrialspecialty mills (same)

Environmental

  • energy_usemoderate
  • waste_streamminimal — cold-work, no melt loss
  • consumablesdrawing lubricant, mandrels