another factor to include is the shell direction (top vs bottom)
the method you describe is the one that i use. in 2012 before we had the render shell thickness option, the key was to remember that the thickness was created in the direction of the bottom shell surface. so if you choose the surface of your part that will be the top of the shell. it is the top of the shell in the mesh. and you choose the top offset option, the midplane will be halfway "below" (direction normal of the bottom shell surface) the surface you're using.
there are some really good articles on this in the solidworks KB that you can access at customerportal.solidworks.com if you're on subs.
also, i think we'll see some enhancements on this in the 2014 version. beta is only a few weeks away for us to check it out!
I just checked and it seems it's still behaving that way. This method should work well for converting solids into surfaces with the offset 0 surface command where you do single selections, but what do you do if you use mid surfaces with 0% position? I often go this way because it allows more flexibility. I guess I could experiment the order of selections and see if it's repeatable.
Also what if you model surfaces from scratch instead of solids. Say when you do just the FEA problem as the solid is existing or was modeled in a different packge?
Thanks for your input JC; it's a good start for me mate
see bert-jan's response. top and bottom always exist and are unrelated to your selection. it is the mesh that decides top and bottom. you can flip if you want.
You say they're unrelated however 0 offset surfaces seems to work the way you described and I recall now reading in my old CosmosWks training material about this rule: Selected face of a solid, towards viewer = top; away from viewer = bottom. But that was 2004 and I haven't got the books anymore to double check.
Further I was wondering if there's any way to decide in advance the default orientation prior to meshing for other techniques of surface modelling. Some of them introduced more recently. I will try find a relation if there is one.
I take it that I was unclear in my initial question. I'm talking about a few steps prior to meshing during the simplification process; is there a way to control which direction will be top/bottom when creating the surfaces? After the meshing of course the orientation is clearly shown whether orange/grey or 3d surface mesh, but this is as I said - Hit & Miss approach.
Thanks for your time guys;
the direction of top/bottom is chosen by the mesher. there may be a convention like you describe but i've never relied on that because I've seen it to be different, especially if you have the option to align shell directions enabled.
in the end, to answer your question, define your shells, mesh to look at top and bottom and then go back and set your offset and then verify with 3d rendering.
i'd suggest submitting an enhancement requests through customerportal.solidworks.com asking solidworks to provide the 3d rendering preview right in the defintiion window. that would solve your problem.
A 2D mesh will show you two colours on every surface (default is orange and grey). Orange is the bottom face, grey the top. If you select a surface to have a bottom offset (-0.5) the shell thinkness will go from the orange coloured face in the direction of the grey face. If you select top offset (+0.5) it will go from grey to orange. Any offset in between will probably work the same way.
To flip a shell, select the body and right click on the mesh icon in the tree. There should be a "flip shell elements" option.