How to Set Grain Direction for Boards and Parts in Grainline Layout
Tell Grainline Layout which way the grain runs on a board and which parts must follow it, so visible parts keep their grain and hidden parts stay free to rotate.
This page covers the grain settings in Grainline Layout. For which way plywood grain runs and when it matters, see Plywood Grain Direction: Which Way It Runs and When It Actually Matters.
How Grainline thinks about grain
Grainline Layout uses a unique, intuitive approach to grain. Instead of forcing you to memorize which side of a plywood sheet is "Length," we focus on your design intent.
Grainline keeps board grain and part grain separate, so you can preserve appearance where it matters and leave other parts flexible.
1. For Your Board: The "Longer vs. Shorter" Rule When adding a board (e.g., a sheet of Plywood), you don't need to worry about which dimension you typed into the "Length" box. You simply tell Grainline Layout where the grain actually flows:
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Longer edge: The grain follows the longest dimension of the sheet (standard for most 4x8 plywood).
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Shorter edge: The grain runs across the width (common for some specialty veneers).
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None (e.g., MDF): No grain constraints. All parts will rotate freely to save you material.
2. For Your Parts: The "Reference Edge" Rule For parts, Length is your Grain Reference. If you want the wood grain to run along a specific edge, define that edge as Length, then set Grain direction to Along length.
It doesn't matter if your Length is smaller than your Width. Grainline Layout treats "Length" as your "Grain Line," not necessarily your "Longest Side."
3. How the Math Happens When you click Run optimization, Grainline Layout performs a "Logical Handshake":
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It identifies the grain direction on your Board (whether it's on the 2440mm side or the 1220mm side).
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It takes your Part intent (e.g., "Must be along Length").
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It locks the part in the orientation that satisfies that intent.
If you set a part to Not important, the "handshake" is ignored, and the algorithm rotates the part 90° whenever it can save you more material.
Why not just use Rotate?
Instead of manual rotation, Grainline Layout focuses on your design intent. Many woodworkers—especially those using track saws or circular saws—think in terms of wood grain, not geometry.
When you are at the workbench, you don't care about the degrees of rotation; you care if the grain on that drawer front flows beautifully with the rest of your cabinet. Grainline Layout handles the underlying math, automatically orienting every part so that your intent matches the reality of the board. This allows you to stay focused on your project and your craft, while we ensure the layout is structurally sound and visually consistent.
A common mistake
One easy mistake is leaving grain direction unrestricted on visible parts just because the layout looks better that way.
That can produce a plan that is efficient on paper but wrong for the finished project.
The opposite mistake also happens: locking grain direction on every part, including hidden parts that do not need it. That removes useful rotation choices for no real benefit.