You seem to be implying that when you create a sales order record you always want to create exactly one corresponding production order record. If the relationship is one-to-one, why not store all fields for sales order and production order in a single table (much easier to manage). You can then manage who sees what fields through seperate forms.
If you really want to do it with seperate tables (the harder way) then you will need an "after update" event to create the new record e.g. by running a query that creates new records for all records in sales order that don't have a corresponding record in production order.
Whilst creating an after update is in itself is straight forward, consider how you will manage someone cancelling an order or maybe editing it. How will you continually keep the corresponding production records in sync. Hence maybe better to use one table.
See your point but unfortunately I wrote this application a few years ago and since then it has grown to rely on the 2 tables. I simplified my origional post when indeed it goes a lot further. Basically, we have 1 form that the user has allways entered the order number twice, sales, production. I want to save them some work!