Ok I'm under standing more now.!!

Quote Originally Posted by paul_m View Post
I then mirrored the part to produce left and right, when I noticed the construction lines for the holes I deleted it. this removed the holes from the initial part, the mirrored part.
You can't delete any geometry if it is related to another operation and if you do then that operation is affected which is why you lost the holes etc. In this case just Hide the sketch with construction geometry on it not delete it.

Quote Originally Posted by paul_m View Post
when i deleted the initial part to keep my new mirrored part, it left a square of construction hanging in the middle of the page.
deleting anything removes the holes from both parts
Same thing happening here. The sketch with construction geometry is related to the Crvpattern2 so if you delete the sketch you affect the pattern and it is removed. If you hide Sketch8 all willl be correct.