Moire test
thingiverse
Print to test if you have moire. It's a cube a little rotated, to force very slow movements in the x and y axis. If you see diagonal or vertical ripples you must hack yours drv8825 drivers with diodes as say in the following post: http://www.engineerination.com/2015/02/drv8825-missing-steps.html
Download Model from thingiverse
With this file you will be able to print Moire test with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Moire test.