Sheet Bending Chart

Press brake force and V-die selection, minimum radius and springback by material, bend allowance, bend deduction and K-factor for flat lengths, and manual folders (bending brakes) - capacity, setting up, boxes and hems.

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Air bending guide figures - check the machine and tooling ratings, and bend a test piece.

Press brake force and V-die

Punch, sheet and V-die in air bending

Force in tonnes per metre of bend - mild steel (Rm 450 N/mm2)

S mm \ V mm	4	6	8	10	12	16	20	25	32	40	50	63	80	100	125
0.5	4.1	2.7
0.8		6.9	5.2	4.2
1		11	8.1	6.5	5.4
1.2			12	9.4	7.8
1.5				15	12	9.2
2					22	16	13	10
2.5						25	20	16
3							29	23	18
4								42	33	26	21
5									51	41	33
6										59	47	37
8											83	66	52	42
10												103	81	65	52
12													117	94	75
15														147	117

V-die opening

V opening mm	Inside radius Ri	Min flange b	Best for S mm
4	0.6	2.8	0.4 - 0.7
6	1.0	4.2	0.6 - 1
8	1.3	5.6	0.8 - 1.3
10	1.6	7.0	1 - 1.7
12	1.9	8.4	1.2 - 2
16	2.6	11.2	1.6 - 2.7
20	3.2	14.0	2 - 3.3
25	4.0	17.5	2.5 - 4.2
32	5.1	22.4	3.2 - 5.3
40	6.4	28.0	4 - 6.7
50	8.0	35.0	5 - 8.3
63	10.1	44.1	6.3 - 10.5
80	12.8	56.0	8 - 13.3
100	16.0	70.0	10 - 16.7
125	20.0	87.5	12.5 - 20.8

Other materials

Material	Rm N/mm2	Tonnage x	Min inside radius	Springback
Mild steel S275, DC01 / CR4	400 - 450	1.0	1 x S (0.5 x S cold rolled)	1 - 2°
Galvanised, Zintec	350 - 450	1.0	1 x S	1 - 2°
Structural S355	490 - 630	1.3	1.5 - 2 x S	2 - 3°
Stainless 304 / 316	600 - 700	1.5	1 - 2 x S	3 - 5°
Aluminium 1050 / 1100 (soft)	70 - 110	0.2	0 - 0.5 x S	about 1°
Aluminium 3003, 5052-H32	150 - 230	0.5	1 x S	1 - 3°
Aluminium 6061-T6, 6082-T6	290 - 310	0.7	3 - 4 x S - cracks if tighter	3 - 6°
Brass (half hard)	350 - 450	0.9	1 x S	2 - 3°
Copper (soft)	220 - 250	0.5	0 - 0.5 x S	about 1°
Wear plate (Hardox 400 type)	1250	2.8	3 - 4 x S, across the rolling direction	10° +, test first

Flat lengths

Bend allowance, bend deduction and flat length

Bend deduction (mm) for 90 degree bends

S mm \ R mm	0.5	1	1.5	2	3	4	5	6	8	10	12	16
0.8	1.47	1.59	1.75	1.92	2.30
1	1.82	1.92	2.06	2.23	2.59	2.97
1.2		2.25	2.39	2.54	2.89	3.26
1.5		2.77	2.88	3.02	3.34	3.70	4.07	4.45
2		3.64	3.72	3.84	4.13	4.46	4.81	5.18	5.94
2.5			4.59	4.68	4.93	5.24	5.57	5.93	6.66	7.42
3			5.47	5.53	5.76	6.04	6.35	6.69	7.40	8.14	8.91
4				7.29	7.44	7.67	7.95	8.26	8.92	9.62	10.36	11.88
5					9.17	9.35	9.59	9.87	10.48	11.15	11.85	13.32
6					10.93	11.07	11.27	11.51	12.08	12.71	13.38	14.80
8						14.58	14.70	14.88	15.35	15.90	16.51	17.84
10							18.22	18.34	18.71	19.19	19.73	20.96

K-factor (DIN 6935)

R / S	K-factor
0.5	0.25
0.75	0.29
1	0.33
1.5	0.37
2	0.40
3	0.44
4	0.48
5	0.50

Sheet gauges

Gauge	SWG mm (British)	SWG inch	US steel gauge mm
8	4.06	0.160	-
10	3.25	0.128	3.42
11	2.95	0.116	3.04
12	2.64	0.104	2.66
13	2.34	0.092	-
14	2.03	0.080	1.90
16	1.63	0.064	1.52
18	1.22	0.048	1.21
20	0.91	0.036	0.91
22	0.71	0.028	0.76
24	0.56	0.022	0.61
26	0.46	0.018	0.45
28	0.38	0.015	0.38
30	0.31	0.012	-

Manual folders (bending brakes)

Manual folding machine - bed, clamp beam, bending leaf and setback

What your folder will take - by its mild steel rating (mm)

Machine rated (mild steel mm)	Stainless 304	Galvanised	Aluminium 1050 soft	Aluminium 5052-H32	Copper soft	Brass half hard
0.6	0.4	0.5	1.2	0.8	0.8	0.6
0.8	0.5	0.7	1.6	1.1	1.0	0.8
1	0.7	0.9	2.0	1.4	1.3	1.0
1.2	0.8	1.1	2.4	1.7	1.6	1.2
1.5	1.0	1.4	3.0	2.1	2.0	1.5
2	1.3	1.8	4.0	2.8	2.6	2.0
2.5	1.6	2.2	5.0	3.5	3.2	2.5
3	2.0	2.7	6.0	4.2	3.9	3.0

Setting the clamp beam

Setting	Clamp beam nose set back from the bending edge	Result
Sharp bend	1 x S	Inside radius about S - normal setting
Radius bend	1.5 - 3 x S, or a radius nose bar	Larger radius - use on aluminium 6xxx, stainless, thick sheet
Too close	Under 1 x S	Leaf pinches the sheet - marks, cracks, strains the hinges
Leaf offset	Lower the bending leaf by 1 x S	Keeps the leaf face under the sheet so it bends, not wipes

Short work

Work length (% of machine)	Thickness x rating
100%	1.0
75%	1.15
50%	1.4
25%	2.0 - clamp limit first

Box blank folding order and hem types

Hems

Hem	Flange length	Notes
Closed (flattened)	4 x S, at least 6 mm	Fold to about 135°, then flatten under the clamp beam. Soft steel and aluminium only - cracks stainless over 1 mm
Open	4 x S, at least 6 mm	Leave a gap of at least 1 x S - takes a wire or another sheet
Teardrop	4 - 6 x S	Rounded fold, inside diameter at least 1 x S - for harder material
Safe edge on a box	2 x hem + fold	Hem the edges before folding the sides up

Folding problems

Problem	Likely cause	Fix
Angle opens in the middle of a long bend	Beam and leaf deflect - work near the capacity	Use lighter material, centre the work, adjust the leaf crowning if fitted
Bend line wanders, sheet creeps	Clamp not tight or setback uneven end to end	Re-set the nose parallel to the bed; clamp harder
Cracks on the outside of the bend	Setback too small, hard temper, bending along the grain	More setback or a radius bar; bend across the rolling direction
Angle short after release	Springback	Overbend: mild steel 1 - 2°, aluminium 2 - 3°, stainless 3 - 5°
Last side of a box will not fold	Fingers too wide, or folding order wrong	Fingers = inside width less 1 - 2 mm; fold the long sides first
Scratched or marked finish	Grit on the beam, sharp nose	Clean the beams; protective film or tape on the sheet

S mm \ V mm	4	6	8	10	12	16	20	25	32	40	50	63	80	100	125
0.5	4.1	2.7
0.8		6.9	5.2	4.2
1		11	8.1	6.5	5.4
1.2			12	9.4	7.8
1.5				15	12	9.2
2					22	16	13	10
2.5						25	20	16
3							29	23	18
4								42	33	26	21
5									51	41	33
6										59	47	37
8											83	66	52	42
10												103	81	65	52
12													117	94	75
15														147	117

Machine rated (mild steel mm)	Stainless 304	Galvanised	Aluminium 1050 soft	Aluminium 5052-H32	Copper soft	Brass half hard
0.6	0.4	0.5	1.2	0.8	0.8	0.6
0.8	0.5	0.7	1.6	1.1	1.0	0.8
1	0.7	0.9	2.0	1.4	1.3	1.0
1.2	0.8	1.1	2.4	1.7	1.6	1.2
1.5	1.0	1.4	3.0	2.1	2.0	1.5
2	1.3	1.8	4.0	2.8	2.6	2.0
2.5	1.6	2.2	5.0	3.5	3.2	2.5
3	2.0	2.7	6.0	4.2	3.9	3.0

S mm \ V mm	4	6	8	10	12	16	20	25	32	40	50	63	80	100	125
0.5	4.1	2.7
0.8		6.9	5.2	4.2
1		11	8.1	6.5	5.4
1.2			12	9.4	7.8
1.5				15	12	9.2
2					22	16	13	10
2.5						25	20	16
3							29	23	18
4								42	33	26	21
5									51	41	33
6										59	47	37
8											83	66	52	42
10												103	81	65	52
12													117	94	75
15														147	117

Machine rated (mild steel mm)	Stainless 304	Galvanised	Aluminium 1050 soft	Aluminium 5052-H32	Copper soft	Brass half hard
0.6	0.4	0.5	1.2	0.8	0.8	0.6
0.8	0.5	0.7	1.6	1.1	1.0	0.8
1	0.7	0.9	2.0	1.4	1.3	1.0
1.2	0.8	1.1	2.4	1.7	1.6	1.2
1.5	1.0	1.4	3.0	2.1	2.0	1.5
2	1.3	1.8	4.0	2.8	2.6	2.0
2.5	1.6	2.2	5.0	3.5	3.2	2.5
3	2.0	2.7	6.0	4.2	3.9	3.0

S mm \ V mm	4	6	8	10	12	16	20	25	32	40	50	63	80	100	125
0.5	4.1	2.7
0.8		6.9	5.2	4.2
1		11	8.1	6.5	5.4
1.2			12	9.4	7.8
1.5				15	12	9.2
2					22	16	13	10
2.5						25	20	16
3							29	23	18
4								42	33	26	21
5									51	41	33
6										59	47	37
8											83	66	52	42
10												103	81	65	52
12													117	94	75
15														147	117

Machine rated (mild steel mm)	Stainless 304	Galvanised	Aluminium 1050 soft	Aluminium 5052-H32	Copper soft	Brass half hard
0.6	0.4	0.5	1.2	0.8	0.8	0.6
0.8	0.5	0.7	1.6	1.1	1.0	0.8
1	0.7	0.9	2.0	1.4	1.3	1.0
1.2	0.8	1.1	2.4	1.7	1.6	1.2
1.5	1.0	1.4	3.0	2.1	2.0	1.5
2	1.3	1.8	4.0	2.8	2.6	2.0
2.5	1.6	2.2	5.0	3.5	3.2	2.5
3	2.0	2.7	6.0	4.2	3.9	3.0