· KAIPU Engineering · glossary · 2 min read
Clearance Angle — Industry Glossary Entry
Definition of clearance angle (also called relief angle) in industrial cutting: the angle of the back face behind the cutting edge, the substrate-by-substrate range, and how it interacts with hone and burr.
Clearance angle (also: relief angle, back angle) is the angle of the back face of an industrial cutting edge, measured from a line perpendicular to the cut direction to the back face of the knife. The clearance angle lets the cut substrate separate from the knife after the cut, and it is the second-most-important edge-geometry parameter after hone.
Typical ranges by substrate:
| Substrate | Clearance angle | Hone | Why |
|---|---|---|---|
| Paper, light packaging | 18–22° | 5–10 µm | Standard; clean cut, moderate burr |
| Tissue, non-woven | 25–30° | 10–15 µm | Softer material peels away; larger clearance helps |
| Film, foil (PE, PP, PET, Al) | 18–22° | 5–10 µm | Thin material, low drag |
| Plastic (neat) | 18–22° | 5–10 µm | Standard |
| Plastic (glass-filled) | 15–20° | 5–10 µm | Abrasive — slightly tighter clearance for edge support |
| Stainless steel strip | 18–25° | 5–10 µm | Work-hardening — larger clearance for chip flow |
| Plate shear (carbon steel, ≤ 6 mm) | 12–18° | 0.05–0.10 mm chamfer | Thick section — small clearance for strength |
| Plate shear (stainless, ≤ 4 mm) | 10–15° | 0.10–0.15 mm chamfer | Work-hardening — even smaller clearance for strength |
| Granulator bed knife | 12–18° | 0.10–0.20 mm chamfer | High impact — small clearance for edge support |
| Granulator rotor knife | 10–15° | 0.20–0.30 mm chamfer | Maximum edge support |
Common mistakes:
- Too much clearance. A 30° clearance on a 0.1 mm strip will not support the cut; the knife digs in, the strip wrinkles, the burr grows.
- Too little clearance. A 10° clearance on a 0.5 mm sheet will drag; the substrate sticks to the back of the knife; the cut tears instead of shears.
- Clearance on the wrong face. On a single-bevel knife, the clearance is on the back face. Some re-grinders grind both faces equally, which doubles the effective clearance angle and breaks the geometry.
- Inconsistent clearance around the perimeter. On a circular slitter, the clearance should be uniform. A re-grind that left the centre 2° different from the edge will wear unevenly.
Relationship to hone: the clearance angle is set behind the hone. A 5 µm hone at 20° clearance means the clearance starts 5 µm behind the very tip of the edge. A larger hone or a larger chamfer consumes more of the clearance angle’s effective range, so a 0.10 mm chamfer at 15° clearance starts the chamfer 0.10 mm behind the tip.
See also: Hone (micro-hone), Burr, Chipping, The KAIPU 5-Factor Blade Selection Framework.