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How to Bend Sheet Metal


With just a few simple tools, such as a vise and hammer, you can bend sheet metal by yourself – for auto restoration, home decoration, light metal fabrication, etc. The size and thickness of the sheet will determine whether the job can be accomplished with hand metal bending or will require the help of a metal bending machine, or brake.

Bending is Not for All Metals


Sheet metals come in a range of sizes and gauges (thicknesses). Some sheet is more brittle than others and may break if bent too far, so you may want to test a small sample before committing to a large project.

Bending a piece of metal will cause it to stretch on the outside of the bend (and compress the inside). That means the finished length will be longer than the original sheet length, so include that in your calculation when sizing the sheet.

How to Calculate Bend Deduction


The total amount stretched is called the bend deduction – because that amount must be subtracted from the starting length of the piece in order to end up with the correct length after bending.

The bend deduction calculation depends on several factors, including:


  • Thickness of the material

  • Outside bend angle (180° minus the inside bend angle)

  • Inside radius of the bend

  • The K factor, a constant based on the material’s properties and thickness

The K factor of your metal sheet, and the calculation of bend deduction, may require a few different sample bends. You can estimate the bend deduction using this chart, which uses an assumed K factor of 0.33, or plug your values into a design software such as Solid Edge, Solid Works or Pro-Engineer.

The Bending Process


Mark the two lines on the sheet metal where the bend will begin and end (the material between these two marks – the bend allowance – will deform to create the angle).

To create the bend manually you can use a shaped form, perhaps made of wood, which conforms to the bend radius you want to achieve. The form should be wider than the metal sheet you are planning to bend.

Set the form into a heavy vise so that the curved radius faces up. Next, place the metal piece into the vise right next to the wooden form and clamp it securely. Make sure the first bend mark lines up exactly with the curve in the form, so that the bending will begin in the right spot.

Using protective gloves hold the free end of the metal sheet with one hand and with the other hand use a mallet or hammer to begin bending the sheet down and around the curved radius of the wood form. Start at one end and slowly work down to the other

To help the bending process you could apply some heat, which softens the metal, making it easier to work.