One problem that comes up from time to time with CNC machining is ensuring your machine is square. Here’s a troubleshooting procedure we recommend at our company, but it might be applicable to other machines, as well.

There are a number of good ways to evaluate whether your tool is “square”.

• The first is to just cut a large rectangle, the bigger the better, and measure the diagonals. They should be equal.
• Short of cutting something out, you can use a V Bit to inscribe a shallow, large square or rectangle (e.g. 30 inches x 50 inches or 750mm x 1250mm) on your table surface (or put a pencil into the spindle and draw one) and measure the diagonals.
• Alternatively, drill 4 holes at the corners of a square and measure the diagonals.
• In all cases, if the diagonals are equal your tool is cutting square.
• If your tool is not cutting square (the diagonals are not equal), the problem can be as easy as pulling the gantry into square using your end stops, or as involved as making adjustments to your gantry or table.

Squaring your tool using end stops
If the end stops were properly set up during tool installation, then they will be squared to each other. In this case you can then use them to pull the gantry into square before you engage the motors/drivers. The motors will hold the gantry in place as long as they are engaged and powered. This misalignment typically occurs when someone moves one side of the gantry while the tool is powered off by leaning or bumping into it. It is recommended to align the motors to each other before every start-up.

Check to see if gantry is out of square
If squaring using the end stops does not work, your end stops are not in the proper location or the gantry itself may be out of square. 

Try dropping the pinion gears out of the rack and rolling the gantry along the rails. Do all the wheels roll smoothly all along the rail? Do both sides of the gantry sit at the same location near the end of the rails? If not, the gantry is out of line.

Check to see if table is out of square
To check if the table is square, measure the diagonals on the table as shown in the image. They should be equal, but if they are not, refer to your original manual for information on how to square your table. 

Please note that if a CNC is cutting square, but fails this test (typically because rails are parallel even if not exactly identical) then you may not need to take any corrective action.

Source: ShopBot Tools. For information call 888-680-4466 or visit shopbottools.com. Excerpted from bit.ly/ShopBot-troubleshooting.