Multi-Piece Miter Elbow Layout
Per-cut miter angle, weld count, and cutback for an n-piece lobster-back miter elbow.
Example
You enter
- Total turn angle (deg) 90
- Number of pieces (>= 2) 3
- Pipe outside diameter (in) 12.75
You get
- Miter angle per cut (deg) 22.5
- Cutback, long side minus short side (in) 5.2812
- Welds (cuts) 2
Checked against published worked examples from: NCCER Pipefitting / standard fabrication references (by name).
Details, formula, and sources
Formula or tableFor an n-piece miter turning total angle A: n-1 cuts (welds); cut angle theta = A/(2*(n-1)) from square; cutback = OD * tan(theta). End pieces are half-gores. With a centerline radius R each middle gore is a straight piece 2 R tan(theta) long on the centerline, 2 (R + OD/2) tan(theta) on the heel and 2 (R - OD/2) tan(theta) on the throat.
Source and editionMulti-piece (lobster-back) miter-elbow geometry - the per-cut miter angle A/(2*(n-1)) and the OD*tan(theta) cutback - as taught in NCCER Pipefitting and the standard fabrication references, by name; first-principles geometry.
Free accessPublic first-principles geometry. The welding procedure, the bevel, and the engineer of record govern the fabricated fitting.
What governsEstimate. AHJ and licensed professional govern.
API field namestotal_angle_deg, pieces, outside_diameter_in, miter_angle_deg, cutback_in, n_welds
- Fabrication the welding procedure, bevel, and engineer of record govern the finished fittingfabrication reference