Sheet Metal Bending

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Sheet Metal Bending: Finding the K-factor

Most of the cheat sheets I have seen through the years are of Bend Compensation, and they were calculated using a consistent rule for the k-factor. The down side is they are only for 90 degree bends and the results are typically rounded off.

The good news is that these charts can be reversed to find that k-factor and then the result can be applied to your other angles of bend. Let’s take a look at an example. I have only shown a portion of the bend chart to save space. Besides, my values for sheet metal bending are not real and you don’t want to use them in your real work.

Thickness	Radius
Thickness	0.0156	0.0313	0.0469	0.0625
0.036	0.0625	0.078	0.078	0.078
0.048	0.078	0.094	0.094	0.094
0.0598	0.109	0.109	0.109	0.109
0.075	0.125	0.141	0.141	0.141

The Bend Calculator makes it really easy to find the k-factor used here. Since the chart is for 90 degree bends and shows the material thickness and inside radius, all you have to do is plug the numbers in and go.

Give it a try. Click on the link to the Bend Calculator. Then enter the Material Thickness of '0.048', the Inside Radius of '0.0313', and the Angle of '90 degrees'. Up above, select the Outside Bend Compensation radio button and enter the value from the chart above, '0.094'. With a little rounding off, I get the k-factor of 0.42.

Keep in mind many of these charts for sheet metal bending are very old and tolerances were not what they are today. The numbers may have been rounded off for convenience. Also as the ratio of the radius to thickness changes, the k-factor may also change.