Punching Round Holes in Steel

Tons to Punch Round Holes in Mild Steel Cold
Diameter Inches	Thickness - Inches
Diameter Inches	.015	.020	.032	.063	.074	.090	.125	.188	.250	.313	.375	.438	.500
.188	.27	.35	.57	1.1	1.3	1.6	2.2	3.3	N/A
.250	.35	.50	.75	1.5	1.7	2.1	2.9	4.4	5.9	N/A
.313	.44	.59	.94	1.9	2.2	2.7	3.7	5.6	7.4	9.2	N/A
.375	.53	.70	.81	2.2	2.6	3.2	4.4	6.6	8.8	11	13	N/A
.438	.62	.83	1.3	2.6	3.1	3.7	5.2	7.8	10	13	15	18	N/A
.500	.71	.94	1.5	3.0	3.5	4.2	5.9	8.9	12	15	18	21	24
.625	.90	1.2	1.9	3.7	4.4	5.3	7.4	11	15	18	21	26	29
.750	1	1.4	1.6	4.4	5.2	6.4	8.8	13	18	22	27	31	35
1.00	1.4	1.9	3	6	7	9	12	18	24	30	35	42	47
1.25	1.8	2.4	3.8	7.4	8.8	11	15	22	29	37	44	50	59
1.5	2	2.8	3.2	8.8	10	13	18	26	36	44	53	62	71
1.75	2.5	3.3	5.2	10	12	15	21	31	41	52	62	72	82
2	2.8	3.8	6	12	14	18	24	36	48	59	71	83	95
2.50	3.6	4.8	7.6	15	18	22	30	44	58	74	88	103	118
3.00	4.2	5.7	9	18	21	27	36	54	72	89	106	124	141
3.50	5	6.6	10	21	24	30	42	62	82	103	124	145	164
4	5.6	7.6	12	24	28	36	48	72	96	118	141	165	189

To calculate the force to punch holes in metal you determine the cross section in shear and multiply it by the shear strength of the metal. The formula is Perimeter times thickness times shear. For round holes in steel this is Diameter * PI * 30. Thirty tons being the approximate shear strength of mild steel plus an allowance for friction. Tons are used to aid in press selection and rating. The practical limit for depth of punching cold is the diameter of the hole.

This table and the calculator below use the conservative value of 30 tons rather than the actual force of 25 tons per inch to shear mild steel.

anvilfire graphic (c) 1998 Patrick Dempsey

Punching Round Holes in Steel

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