We often think about the grain in wood and its importance when we’re doing a woodworking project or selecting a piece of wooden furniture. The grain in the wood is more uniform in some wood than in others and working against that grain can be challenging.


The same applies to metal fabrication. Metal contains grain and understanding graining is important for a variety of metalworking processes.

What makes up the grain of metal?


Most metals are not solid but are composed of different crystallites. These crystallites create the metal’s grain. Each crystallite is microscopic, but collectively they form the grain of the metal. When metal is processed, the alignment and direction of crystallites are altered, which causes the metal to have a preferred grain orientation.


The metal’s grain direction is usually only a factor when bending, however. Sharper or tighter bends can often be made across the grain without cracking. The grain direction needs to be considered when the bend radius is less than twice the thickness, depending on the particular material and its hardness.

Why is grain important?


Determining the grain direction in the fabrication process is essential when it comes to understanding how that metal will behave and what the effects will be on its structural integrity and overall strength.


Generally speaking, the smaller the size of the grain, the stronger the metal will be. Getting the process right is critical if metals are going to be bent in a tight radius. Metals that have larger grain sizes can’t be bent in tight radiuses. In practice, this means that they are much more susceptible to failure.


The direction in which you work with the grain is another important factor in the process. For instance, if you’re working with aluminium it’s important to understand whether you’re working with grain in a longitudinal way, or across it in a transverse direction. Whatever the case, the grain will always move in the direction that the metal was milled.


How do you grain metal?


To grain metal to make it more suitable for your particular application involves the use of coated abrasives to remove a top layer from metal blanks. This is typically done with a sanding belt, and grits are normally 120, 180 or 220. Once the initial sanding process is complete, some metals may need to be softened further. This is usually done with a surface sander to help achieve the desired appearance and grain orientation.


Graining is used across a wide range of industries including the military, aerospace, audio, telecommunication and medical devices. While it is a relatively simple process it can cause significant issues if it is neglected.


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Metal Graining Before & After

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