You need to link FROM the main table TO the code table.  If there is any chance that the main table will have a blank field instead of a value, you need to then righ-click on the join in the Database Explorer and make the join a "Left Outer" join.  That will return all of the records from the main table regardless of whether they have a corresponding value in the code table.  Then put the Production Description on your report.

So a record can have two machine codes, each of which connects to a different record in the lookup table?  If so, they you'll need to add a second copy of the table to the report.  When you try to add a table that already exists in the report, Crystal will throw up a warning and ask if you want to "alias" the table.  It will then add the table with "_1" at the end of the name.  You then link from MachineCode1 to the original version of the lookup table and from MachineCode2 to the "_1" version of the lookup table.