Thanks HuFlungDung...
But I'm still not very sure what I should do, the screw that you mentioned, is it item 26,27,31 and 32 (by refering to the 4020A parts manual page 4)? And which part is the gib and where are the ways? Can you please illustrate more (by refering to the parts manual) for me? Sorry I'm still quite new to the mechanical part of the machine... Thanks in advance...
Just in case you don't have the manual on hand, you can find it here:
http://www.fadal.com/ie/manuals/manuals1.asp