First off, attribution: This is a remix of the laser bed corner inserts by morpha on thingiverse.

Found here: https://www.thingiverse.com/thing:4857543

During my testing, I figured out the true 0,0 of the Snapmaker A350 (at least mine) is at X-2, Y15. So I modified this laser bed square to be 15mm on the Y and flush with the X side, also removed one row of pegs so it does not collide with the gantry. In the 3mf I also included a negative space to notch the corner to provide a more accurate square (since 3d printing can't do perfectly square corners).  I also included a mirrored one to put on the other side in the Y, ensuring the item to be burned is square all the way up, use regular clips/plugs on the opposing side to ensure it doesn't move. Just insert it into the laser grid table flush with the front, place your item into it, and the opposing one on the opposite side.

Using these allows me to accurately, and repeatably, place objects on the bed to be laser engraved/cut and gives me an actual origin point. I just have to remember to compensate those 2mm on the X axis and the laser is exactly on the corner every time. Then I can accurately place my project where I want it to be without guessing.

I only have one Snapmaker, but I can assume the limit switch and home setups are the same across machines. However, you can test where your “true origin” (machine zero) by squaring up a piece of paper on the laser bed in the front, left corner, homing the machine, and setting the Z height. Then, jog the machine to machine 0,0 on X/Y, set origin, then jog out 10mm in both X/Y. Turn on the laser for a second to burn a tiny hole in the paper, then using calipers measure the distance on X/Y to the center of the dot, and subtract 10. My measurements were 8,25 so -2,15 is my machine zero. For CNC operators/machinists, having repeatability in an origin is key to quality products and accurate parts.

EDIT: After receiving the new 10W laser module, I had to find the new origin, it changed to X5.5Y-9, so I modified and uploaded the new alignment guides for it as well and named them accordingly.