Carving Depth Varies

I am new to this and have just recently purchased my X-Carve 1000mm. I have assembled it all and have attempted some practice cuts, which have turned out rather well. I have been trying to get a piece to carve but every time I try the depth of the cuts varies. It ends up being deeper on the bottom and shallower near the top but is uniform across the x axis and as you can see in the image it is quite bad. Any help would be greatly appreciated!

Wasteboard may vary in height. Take measurements from various locations on the wasteboard to confirm

  1. Make sure your Y rails are parallel to the waste board
  2. skim your wasteboard as Phillip suggested
  3. make sure your board isn’t uneven thickness
  4. make sure you have the same clamping force on both the bottom and the top.
  5. where/how are you setting your Z zero?

use a good base for your machine is prepare it myself with aluminum bars.

I measured the wasteboard and it has a variance of .0125in from front to back (deeper in the front just like the picture shows. How would i fix this issue? The board seems to be the same thickness and is parallel with the Y rails. I have been setting my zero with the probe.

Thank you, I believe I have the issue fixed. I shimmed the side rails as needed to bring the machine up in the front.