Hi,
I assume you may have solved this by now but the reason they will all change to hard edges is because you make your model in smooth mesh preview which is what it exactly what it says, a preview. So when you try combine the two objects the smooth mesh preview object will revert back to the hard edged model.
To prevent this from happening, you can either;
Add more polygons while modelling initially 'without' smooth mesh preview active, turning it on every now and then for reference.
Or the real easy method, select the object you want to stay smooth, go to modify-convert-smooth mesh preview to polygons
This will change the smooth mesh preview to an actual model with more polygons and you should have no problems combining it with the rest of your model
Hope this helps
Ever Try, Ever Fail, No Matter. Try Again, Fail Again, Fail Better.
Last edited by mendosa69; 10-01-2015 at 09:01 PM.