mirror and joint

when i mirror an object and then joint it to make a new object
half of the normal are reversed or about half but not always

is there a way to do a mirror with the normal in the proper orientation i mean outside
and not inside after a join ?

so now i do the Ctrl-a then flip the normal then do the joint and eveything seems ok with the normal - all outside

there must a more direct way of doing this !

Thanks

You could use a “Mirror” modifier instead of the mirror command. That will preserve your normals.

If you need to repeatedly mirror parts of the mesh you’re working on without mirroring the whole thing, you’re stuck. Normals are flipped when you mirror vertices. What you can do is hit Ctrl+NKey, which will recalculate all selected normals outside, which is a little quicker than selecting half of the model and then flipping normals.