Gantry y axix not tracking parallel

Recently I was carving and broke a bit due to chips being backed in the path. This also caused the work piece to move from the clamps. After I replace the bit and placed an additional clamp than I had the first time, I began carving the same project. This time I vacuumed the chips as it was carving. As it carved, I noticed one the second path around the square, it was not carving square on the y axis and shortly after it again moved the work piece from the clamps. I removed the work piece and lowed the bit to the board and started from the left to the right and saw it was not parallel to the lines on the grid. I also found the lower adjustable v wheels had 2 that will not move freely even after I adjusted them. Does anyone have any advice

make sure that your machine was put together square.

other than that you can use a set of 1-2-3 blocks to square your axis before starting the machine. you can use whatever you have on hand but they need to exactly the same size.

start the machine and run the homing sequence or manually run it as far forward as possible and power it off, then before powering it back on place them (blocks) between the risers on the front and manually bump the rail to ensure that is parallel to the sides, then when you turn on the machine both will start at the same distance away from the rail.

PawPwas work shop has a good you video on squaring the X carve