Is there any way of improving the Xaxis

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I have been cutting circles which are coming out slightly oval, I have been searching the forum and it all points to it being a mecanical problen such as pulley wheels too loose or too tight or belt too loose or tight, I find it hard to get the pulleys right, they are hard to get at inside the gantry with the allen key, I am using the X controller, I have replaced the Z axis with a linear actuator and that works fine, no belt or pulley wheels to worry about, is there any way to upgrade the Xaxis, the Xcarve is the only CNC machine I have seen so I don’t know much about them