Tubing & Bending Glossary

Short definitions of the terms used across Benders Hub.

Centerline radius (CLR) — Radius of a bend measured from the bend centre to the tube centreline. Dies are specified by tube OD and CLR.
D of bend — CLR divided by tube OD. Lower values are tighter, harder bends.
Wall factor — Tube OD divided by wall thickness. Higher values mean a thinner wall relative to diameter.
Springback — The angle a bent tube relaxes after the bender releases it. Measured with a test bend and compensated by over-bending.
Ovality — How out-of-round the tube becomes in the bend: (maximum OD − minimum OD) ÷ nominal OD.
Tangent point — Where a straight section of tube meets the start or end of the bend.
Tangent length — CLR × tan(angle ÷ 2): the distance from a tangent point to where the straight centrelines would intersect.
Arc length — Length of tube along the centreline inside the bend: CLR × angle in radians.
Rotary-draw bending — The tube is clamped to a rotating bend die and drawn around it, giving a consistent radius.
Mandrel — A support inserted inside the tube at the bend to stop it collapsing or wrinkling.
Wiper die — A tool that supports the inside of the bend just ahead of the bend die to prevent wrinkles.
Pressure die — The die that holds the tube against the bend die as it is drawn around.
Ram (press) bending — A ram pushes the tube between two supports. Inexpensive, but thin-wall tube tends to flatten.
Roll bending — Forming large radii by passing the tube through three rolls several times.
DOM — Drawn Over Mandrel: welded steel tube that has been cold-drawn for consistent size and wall.
ERW — Electric Resistance Welded tube, as welded, without the cold-drawing step of DOM.
4130 (chromoly) — A chromium-molybdenum alloy steel used for lightweight chassis and cages.
NPS and schedule — Pipe sizing: nominal pipe size and wall schedule. Actual OD differs from the nominal size (1-1/2" NPS is 1.900" OD).
Notching (coping) — Shaping a tube end so it fits closely against another tube before welding.