Fix model, recalculate flips the normals? why

Hi all,

i was fixing some imported 3ds chair models. I noticed there where a lot of tris so i changed them to quads cause i think i read thats better. A lot of normals flip to the wrong side than after i do recalculate than> I than need to flip them back by hand. I thought that recalculating a model is good to do? Could anyone point me out here why that happens

first, make sure there are no repeated vertices. ( this is common with imports). Select all verts, press W–>> remove doubles. Then try CTL-N. hopefully that will make the normals consistant

is it a manifold ( one piece ) or non manifold ( combined pieces or pieces with gaps ) ? sometimes with a non-manifold mesh the normals will not recalculate properly and it becomes necessary to do it manually.
(edit) another option is to seperate the pieces and recalculate them while they are seperated either in space, or as objects.