Optimum Gap between Flanged Hole Wall and Bending Edge

Table of Contents

1. Bent part with a flanged (tapping) hole

As shown in Figure 4-17. Its flanged (tapping) hole

The distance L from the hole wall to the bend edge cannot be too small, as it may damage the flange (even prevent it from forming).

Figure 4-17 Bent part with a flanged (threaded) hole

Generally, it is recommended to select L > (7~8)t based on experience. When the structural requirement of the bent part requires a shorter distance from the flanged (threaded) hole wall to the bend edge, the minimum distance should be calculated or graphically determined based on parameters such as material thickness t, flange (thread M) hole (diameter D) size, flange height, folding shape, and bending radius r.

Common Metric Thread Bottom Hole Flange Dimensions

Refer to Table 4-5 for common metric thread bottom hole flange dimensions. Dimension marking examples are shown in Figure 4-18.

Table 4-5 Common Metric Thread Bottom Hole Flange Dimensions (unit: mm)

Thread Diameter d	Material Thickness t	Flange Inner Diameter d₁	Flange Outer Diameter D	Flange Height h	Pre-punch Hole Diameter d₀	Bend Radius r
M2	0. 6	1.6	2. 6 ^+0.16	1.3±0.2	0.8 ±0.1	0.2
	0. 8		2.7^+0.16	1.6±0.2	0.8 ±0.1	0.2
	1		2. 9 ^+0.16	1.8±0.2	1.2 ±0.1	0.4
M2.5	0. 6	2.1	2.9 ^+0.16	1.3±0.2		0.2
	0.8		3. 2^+0.16	1.7±0.2	1.0 ±0.1	0.2
	1.0		3. 5^+0.16	1.9±0.2		0.4
	1.2		3. 5 ^+0.16	2.0 ±0.2	1.2 ±0.1	0.4
M3	0. 8	2.5	3. 6^+0.16	2.0 ±0.2	1.2 ±0.1	0.2
	1.0		3. 6 ^+0.16	2.1 ±0.2		0.4
	1.2		4. 0 ^+0.16	2.2±0.2
	1. 5		4. 2 ^+0.16	2.4±0.2	1.6 ±0.1
M4	1.0	3.3	4.7^+0.16	2.6 ±0.2	1.6 ±0.1	0.4
	1.2		5 ^+0.16	2.8 ±0.2
	1.5		5. 4 ^+0.16	3.0±0.2
	2.0		6 +^0.16	3.2 ±0.2		0.6

Note: This table is applicable for flanging thread bottom holes of low carbon steel, brass, pure and aluminum. The data in the table is for reference only.

Figure 4-18 shows an example of metric thread bottom hole flanging size annotation.

Example 4-1 illustrates a bent part as shown in Figure 4-17. The sheet thickness is t=1.5mm, the thread M4 is tapped on the flange, and the required flange height is H=3.3mm. Calculate the minimum distance from the flange (thread tapping) hole wall to the bending edge.

Solution: Use a 30° bending knife for processing, and the graphical method to calculate the minimum distance from the flange (thread tapping) hole wall to the bending edge.

From the graphical method, we get L=6mm.