The reasons are that is better painted are:
1) The woodgrain is all over the place on pine, and some is a bit darker on the corners than the rest.
2) It is very hard to get a perfectly smooth surface without some areas being more matt than others unless you use a hard wood, which is also harder to work with, unless you have specialist tools, which I don't have.
c_mon seems to have excellent skills with his woodworking; mine are more limited.
3) Joining pieces together and having to angle them to be in line with the adjacent piece is not easy to get right. A couple of the straight edges didn't join 100% perfectly, as it was it would look imperfect - easily rectified with the polyfiller and concealed with the paint. I could have make the two offending pieces again, but I didn't need to.
4) In most places the join between the wood and plastic was seamless; in others there is about a 1/4mm gap, again, polyfiller sorts this out.
5) Pine against plastic looks home-made. The finish I am after is as professional as I can make it, the only way is to make the whole thing look seamless. I don't have vaccum forming equipment or plastic for it, so I am making it this way to make it look (hopefully) as good as if it had been, all be it different as the top of the case is painted under the plastic instead of on top.
I have just applied the first varnish coat, it needs another one later. The paint, as you may have noticed, is described as "10x diamond technology tougher" and the matt varnish is described as extra tough - it is certainly resistant to daily use on the cabinets I make a year+ ago; tough stuff.
I understand
dudex77 why you would have preferred the wood left as it was, but I think you will be very impressed when I take the pics of the case top when the two varnish coats are on and dried and the electrical tape is removed; and therefore see why I decided to do the process I have done.
minkster - You may have noticed I have adopted the name you suggested; unless anyone comes in with a better name for the project!
