Aluminium Window Profile Bending: Radius from Chord and Rise
A circular arch with a 1,200 mm chord and 180 mm rise has a 1,090 mm centerline radius and an arc length of about 1,271 mm.
This application example uses public references and explicitly stated planning inputs. Figures derived from assumptions are estimates for evaluation, not measured customer results.
Production question
What centerline radius should be specified for a circular window arch with a 1,200 mm chord and 180 mm rise?
Worked calculation
The circular-segment equation is R = c²/(8h) + h/2. At c = 1,200 mm and h = 180 mm, R = 1,090 mm. Centerline arc length is about 1,271 mm using 2R × asin(c/(2R)). Stock length also needs unbent ends and trim.
How to validate it on the shop floor
Mark the centerline datum on the drawing and inspect chord and rise after unloading, before trimming. Check cross-section distortion and use a full-size template if the arch must mate with glazing.
What to do with the result
Give the fabricator the centerline radius, chord and rise together, then identify where the straight ends begin. Set aside material for the roll approach and for trimming the ends after bending. A symmetric arc can still fail fit if the end tangents or trim points are wrong. Mark both endpoints and the crown on a template, and check those three references before committing to glazing dimensions.
Practical follow-up
Can the glazing radius be used as the machine target? Convert radii to the same datum first. Inner, centerline and outer radii differ by offsets through the profile depth.