I am a bit rusty on my adjustments and I just noticed something that requires attention but the solution isn’t coming to me.
I am doing a sign using X tiling and it it looks like my Y is 2mm high across the length of the first tile. Test board is secured against the front angle iron (w spacer) sitting directly on the OEM bed. If I zero to the left lower corner my little registration mark that marks the end of the tile/zero 2nd tile is about 2mm high in Y measuring about 23" X to the right.
Adjustment would to lower the right side of the X beam by 2mm. Been a while. How do you true the x-y again? It’s ok to point me at a page in some manual.
You could look at assembly manual. But simplier would be to put a level across bed of machine and level with base feet side to side and front to back. Then move level to Y axis and check level. If necessary the screws in end plates can be loosened and Y rails moved to level. To check for square measure across bed diagionally on both diagionals from known spots to same spot on both sides. Compare measurements. If same the machine is square. If they are not the same take longest diagional and those points need to be pushed to gether by half of difference between two measurements. Recheck measurement and repeat adjustment until they match. A few thoudands wont matter much. The design of the Shapeoko is self squarring. So if your machine is significantly off look at mechanical issues like a leveling foot missing or foreign object under machine before tearing into adjustments.
Well if your bed is not level neither will your rails. So level the bed front to back and side to side before moving on to your Y rails.
So if the bed is not level you cannot level your Y or X rails because what would you be referencing your level on. So if the bed is level you have a reference for the distance your rails are above the base. If you bed is level and your Y rails are level your distance from the base to the bottom and/or top of your y rails will be the same distance.
If you have one corner of your machine lower or higher than the rest you will have issues with projects cutting depths, Lets say the left front corner is 1/8 of an inch lower than the other 3 corners. Well when you cut a pocket that was referenced from the front left corner and then you cut a pocket in the right back corner the right back corner pocket will be 1/8 inch off. Your bit will slam into the flat surface 1/8 inch before it starts cutting because the front left corner is 1/8 inch lower than the back right corner. So this leads to a lot of issues in many different ways. So get your bed level before you start trying to square or level the rails. First things first.