To Create or Modify a Model Grid
You can create a model grid in Part or Assembly mode by clicking the arrow next to Display group in the Layout tab, and then clicking 
Model Grid. and selecting a coordinate system to define the origin of the grid from the Model Grids dialog box. In an assembly, this coordinate system must belong to the top-level assembly.
Model Grid. and selecting a coordinate system to define the origin of the grid from the Model Grids dialog box. In an assembly, this coordinate system must belong to the top-level assembly.1. Open a drawing.
2. Click Layout tab and then click the arrow next to Display group.
3. Click Model Grid. The Model Grids dialog box opens.
Model Grid. The Model Grids dialog box opens.4. Use the various options on the Grids and Settings tabs in the Model Grids dialog box to create the model grid.
To modify the model grid, follow the same procedure.