In order to achieve this, you should set AutoScale property to false.
RadChart1.PlotArea.XAxis.AutoScale = false;
Then, that one option for adding items to XAxis would be to use AddItem method of the Axis inside the same loop:
where label is the string variable which will be added to XAxis.
Hope that helps.
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.