What I have done in the past:
Create a table that has the fields and field sizes you want. (This is important because it you use a macro or make table query, I don't know of the way to control field size.)
Create a delete query to delete all the records in your newly created table. (I know there won't be any in there yet.
Select [File], [Get External Data], and [Link Tables]. Set up a linked table for each of your 20 csv files.
Create an append query for each one of your CSV linked tables that will append to your master table.
I assume that you want this to be a repeatable process, so create a macro in the macro builder to run the delete query and run all of the append queries.