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You don't say what the diameter of the bit is but I'm guessing that is the width of the vertical axis cut. Sounds like you have some play in your horizontal axis that is allowing the spindle to move enough to cause it to cut the extra width. It could also be some play in your spindle mount. Make sure all your connectors are tight, bearings are adjusted if they are adjustable and that the spindle is perpendicular to the bed. Also on these smaller machines don't try to overfeed the bit.
You don't say what the diameter of the bit is but I'm guessing that is the width of the vertical axis cut. Sounds like you have some play in your horizontal axis that is allowing the spindle to move enough to cause it to cut the extra width. It could also be some play in your spindle mount. Make sure all your connectors are tight, bearings are adjusted if they are adjustable and that the spindle is perpendicular to the bed. Also on these smaller machines don't try to overfeed the bit.
