How to create non-resizable font in charts
Select the text item in the chart (a chart title, axis, legend, and so on), and access the Format dialog box for that item. Click the Font tab and specify the font size. Remove the check mark from the Auto Scale check box.
To turn off auto scaling for all text items in the chart, access the Format Chart Area dialog box, choose the Font tab, and remove the check mark from Auto Scale. For best results, do this before making any font formatting changes in the chart - otherwise, all text elements will be formatted identically, and you'll probably need to make additional adjustments.
To turn off auto scaling permanently, you need to make a change to the Windows registry. Use the Windows regedit.exe program and navigate to this key (the "11.0" part will vary, depending on the version of Office installed):
Use Edit -> New -> DWORD value to add a new item named AutoChartFontScaling and give it a value of 0.
This change affects only the charts that you create after making the registry change. Previously created charts are not affected. This registry entry simply controls the value of the Auto Scale check box in the Font tab of the Format Chart Area dialog box.