Chess Board - Parametric Checkerboard Calibration Pattern - FreeCAD - Chess Checkers CV2 OpenCV

If you like this model please heart and download so I can justify making more!

This FreeCAD file makes is ridiculously easy to make a custom checkerboard pattern.  I included a chess pattern (8x8), but you can make whatever pattern you wish by entering in the Width of the square and number of instances in the X and Y in the VarSets section.

Quick Instructions:  

0 - Install FreeCAD V1.1 or higher. https://github.com/FreeCAD/FreeCAD/releases
1 - open ChessBoard-Parametric_V3
2 - enter the desired values into the VarSets section
3 - CTRL-Click on the 3 bodies - WhiteSquares, BlackSquares and Underlayer.
      4 bodies if you want the border.
      (do not select all via CTL-A)
4 - Export to a STEP file.  Make sure you select AP214. De-select all export options.
5 - Import into slicer and do NOT split into objects
6 - now it is easy to select filaments for each body, there should be only 3 groups.

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Make sure you are on V1.1 or higher. As of this writing, V1.1 is a development build, so download the latest weekly FreeCAD Build. 

V1 Notes: 
This is just here to show how the project started off.
V1 File - Enter half the number of squares in the X and Y. 

To make things super simple, the number entered will be 2x the number of x and y squares because it uses a 2X2 base feature for simplicity.  The first 4 squares of a checkerboard.  
Example file uses 4 in the x an 4 in the y, therefore an 8x8 square chess board is produced.   

V2 Notes:  
This file is fantastic!  It allows for an odd number of squares in the X or Y directions.
V2 File - Enter in the total number of squares in the X and Y.  This makes odd numbered sides possible.

It builds on V1 but at the end cuts off the excess squares. It was much easier to build a file that supports odd numbers by doing it this way.  The key was to use the celi() function in the Linear patterns to round up to the nearest integer when dividing by two.  When an odd number is divided by 2, a decimal makes the linear pattern impossible.  Rounding up makes the pattern one square bigger in the X and Y since the base pattern includes a 2X2 square matrix.  The final cut in each square body file, removes the excess.  The simple way of making the cut sketch was to make a binder that was offset by one square length with sharp intersections. FreeCAD has so many awesome features!

V3 Notes:
This file adds the outer border.  If you desire a border, select the type of edges, round or sharp and the thickness and base layer height. This adds to the original base layer, but you need at least one print layer thick. 

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There are two variables in the VarSets section used to display how large your board is.  The base pattern is there to “glue” down the squares in the final print or else they don't bind to anything and are easy to snap off.

By far the easiest way to color these in your slicer is to export them correctly so they come in as three objects with parts inside of them. You can quickly assigned filaments to the Objects that contain all the bodies of the same material.  Select the three bodies shown in the picture and make sure you use the 214AP STEP format or above. Unclick all options to remove any excess geometry being imported.  When importing into your slicer, make sure you don't break up the individual items into bodies. 

If you don't have a material changer you can just make the squares one layer thick and print the base white. There will be one tool change to black you can do manually.  There is no need to make the board one layer higher since there is only one tool change.