A hole can fit on the CAD model yet distort during bending. Check its nearest edge against the fabricator's tooling zone, using the same datum as the supplier's rule.
One supplier's screening rule
SendCutSend's deformation guide keeps cut features outside the die-width area, measured in the flat pattern from the bend centreline. Its published example uses 0.104 in mild steel with a 0.630 in die width. This is a supplier-specific example, not a universal thickness-based clearance.
Define c as the perpendicular distance from the bend centreline to a round hole's centre, d as hole diameter, and e as the nearest-edge distance. Then e = c − d/2. Compare e with half the supplier's die width D. Do not substitute a formed-part tangent or virtual sharp for this flat-pattern datum.
Worked layout check
Use the guide's illustrative die width: D = 0.630 × 25.4 = 16.002 mm, so D/2 = 8.001 mm. The stated stock thickness converts to 0.104 × 25.4 = 2.6416 mm. Assume a plain Ø6 mm hole and two candidate centre positions; these hole dimensions are our own teaching example.
| Candidate | c | e = c − 3 mm | e − D/2 |
|---|---|---|---|
| Initial position | 10 mm | 7 mm | −1.001 mm |
| Moved position | 12 mm | 9 mm | +0.999 mm |
The initial hole overlaps the screening zone. Moving its centre 2 mm farther away places the nominal edge outside that zone. The mathematical boundary is c = D/2 + d/2 = 11.001 mm; do not treat this exact-boundary position as a released manufacturing clearance.
Apply the correct feature boundary
For a countersink, check the outer rim of its major diameter, not just the pilot hole. SendCutSend's separate hole-operation guide distinguishes this check from hardware insertion requirements. A plain-hole calculation must not be reused as approval for an insert or a threaded feature.
- Record material, thickness, selected tool width, supplier guideline revision and the flat-pattern bend datum.
- Check the closest point of a slot or cutout; a centre point alone does not describe its boundary.
- If the location is functionally fixed, discuss an agreed relief or a post-forming machining operation. Recheck strength, access and cost before changing the design.
- Dimension functional holes in the formed part and agree how their position and shape will be inspected.
Technical references
Supplier guidance checked 29 October 2026. The comparison table and calculations are original; no supplier illustrations or handbook tables are reproduced.