Engineering worksheet
Describe the bend.
Calculate an ideal circular arc at the geometric mid-thickness. This does not determine a safe radius, neutral axis or fatigue life.
Arc length = mid-thickness radius × angle in radians. Real bend behavior depends on materials, copper distribution, local construction, restraint and use conditions.
Use one radius convention
State whether a drawing dimension reaches the inside surface or the geometric centerline of the circuit. For the worksheet’s ideal circular arc, the geometric centerline lies halfway through the entered thickness. This bookkeeping convention is not a claim about the mechanical neutral axis. Use the regional thickness worksheet to identify which layers the bend actually contains.
Bend input record
| Input | State explicitly | Why it matters |
|---|---|---|
| Radius | Inside or geometric centerline, with units | Avoids comparing different surfaces |
| Thickness | Finished local stack in the bend | Connects geometry to the actual region |
| Duty | Positions, travel, rate and required service | Defines the validation question |
| Restraint | Clamps, edges, friction and free length | Defines how the shape develops |
Describe how the bend is produced
Document the bend’s endpoints, supports, angle, nearby edges, and available space. Explain whether the circuit wraps a mandrel, forms a free loop, or moves through a mechanism. The duty classification should include assembly and service handling. A controlled installation fold and a repeated sliding loop can share a radius dimension while imposing different demands.
Review the construction and verify the assembly
Record copper, dielectric, coverlay, shielding, and any local changes in the moving span. Mark vias, terminals, and reinforcement edges on the same drawing. Take the resulting geometry record into a representative bend test plan. The test should exercise the intended mounting and motion rather than substitute an arbitrary hand-folded sample.
Before you release the design
- Label the radius convention on both flat and installed views.
- Keep thickness units consistent when using the worksheet.
- Record the minimum-clearance position throughout the motion.
- Identify which production-like samples will represent the final construction.
Watch points
- Do not turn a thickness-to-radius ratio into an automatic pass/fail rule.
- An ideal centerline arc length does not include connector engagement, straight runs, or installation slack.
Practical questions
Can I convert a centerline radius to an inside radius?
For the ideal constant-thickness circular geometry used here, subtract half the thickness after converting units. This describes geometry only and does not resolve material strain or reliability.
What if my flex makes an S-shaped loop?
Describe both curves and their changing positions. A single arc is insufficient to capture that path; exchange a motion model or a sequence of measured positions.
Technical references
References support the material or design context. Check the exact grade, part number, document revision and project conditions before release.Updated 27 September 2026 · Technical content policy · Engineering guidance supports project review; the agreed drawing defines the build.