If your machine gets 0.010" of backlash in one axis, the circles will end up 0.020" out of round. Tight is required!

Since you have just noticed the problem, it is probably something you did that caused the change.

The good news is that its almost certainly a fixable problem, once you figure out just which problem you are having. Fixing the wrong problem can make a problem where there wasn't one. Once you have found the right problem its just a short bit of work to fix it.

Use a dial indicator and measure the play in each axis. Borrow a dial indicator if you don't have one. The more setup you do on your machine the better at it you get.

Good luck, and keep us posted-

D