Hi and thanks for your comments.
I've decided to start over. At first i thought something was wrong with my graver shapes, but after having made a sharpening template, i realized the handle was too big, i could not make anything without my graver slipping across the plate.
I think i spent 3 days trying hard before admitting i had made a mistake somewhere.
So the new handle is cheaper, made out of wood with a hacksaw, a knife and some sandpaper, but it holds only one blade. I guess i'll be doing the next ones with better tools, but for now that's all i had here.
I also used a much smaller diameter steel bar, reducing the overall cost and time involved.
Here are some photos, with the first attempt on using this new graver. Still ugly, but now i'm not slipping anymore, so i guess it's just a matter of time now that i have the right tool.
90°, 'long heel', polished on 1600 grit sandpaper, i'll buy a good stone someday but for now it's too expensive.
(Something strange with the lighting, but the angles are okay, and it's almost mirror polished)
Thanks alot everyone ! I would not have understood graver shapes without your help.