Method for constructing a 90-degree bridge bend

A 90-degree bridge bend can be constructed by cutting and forming two 45-degree sections or by roll bending, using precise measurements and formulas to ensure accuracy.

Cable Tray 90-Degree Bend

For cable tray bridge bends, the process involves creating a 90-degree elbow by forming two 45-degree bends:

1. Determine Bottom Side Length: The bottom side (diagonal) after bending should equal the tray width, typically 100–400mm .
2. Mark Bending Points: Select two points along the side rail at this length and draw perpendicular lines relative to the bottom side. Choose the bending direction and designate the opening side as the bottom.
3. Draw Isosceles Triangles: Draw perpendicular bisectors on the two lines to form two isosceles triangles. The base length is calculated as L = 2 × (tray height × sin 22.5°). For example, a 100mm high tray yields a base of 76.5mm .
4. Cut and Bend: Cut the triangles and bend the tray along the lines to form two 45-degree bends, resulting in a 90-degree elbow. Adjustments for specific tray lengths can be made using basic geometry.
5. Alternative Methods: For miter bends, cut straight sections at 45° (two pieces) or 30° (three pieces) and join them. For roll bending, calculate the arc length along the tray centerline and allow for tray width if needed .

Sheet Metal 90-Degree Bend

1. Mark Bend Line: Accurately mark the line where the bend will occur .
2. Secure Material: Use a bending brake or a vise with angle iron to hold the sheet firmly.
3. Bend Past 90 Degrees: Account for springback by bending slightly beyond 90° (e.g., 92–95°) and check with a protractor or square .
4. Adjustments: Minor corrections can be made with a rubber mallet or by re-clamping and applying additional pressure .
5. Consider Material Properties: Thicker gauges require more force and a larger bend radius to prevent cracking .

Conduit or Pipe 90-Degree Bend

1. Use Deduct Method: Subtract the take-up value (e.g., 5" for 1/2" EMT) from the desired stub height to mark the bend location .
2. Back-to-Back 90s: Use the star or rim notch on the bender to place the second bend accurately. Gain formulas can save conduit length.
3. Check Marks and Angles: Verify with a bender chart or test piece to ensure the final 90-degree angle is correct .

Calculations and Tools

• Bend Allowance: Arc length along the neutral axis, used to determine material needed .
• Centerline Radius: Inside bend radius plus half the profile depth.
• Bend Deduction: Adjusts outside leg dimensions to calculate flat length.
• K-Factor: Estimates neutral axis location, typically around 0.42 for sheet metal .
• Tools: Bending brake, vise with angle iron, protractor, square, cutting tools, and safety gear .

By combining accurate measurements, proper cutting, and controlled bending, a precise 90-degree bridge bend can be achieved in cable trays, sheet metal, or conduit, while accounting for material properties and springback.