Thanks for your help. I had this information, but you gave me more details about it, realy helpfull.
The thing is. it's realy hard to draw a font in "snap to grid", even if you have a file of 2000 em height. It's not realy precise.
I tried to import the glyphs in Fontographer, it look good (but it's hard to see at the same time, the zoom tool never zooming enough). But when I export in postscript to FontLab, strange curves apears...

(but I know than I was not in "snap to grid" mode) grrrrrrrr.....
I'll try again, I think it's the only to do it anyway.
I'll continue to read the Fontlab user manual, I'll find a solution and be a expert soon I hope.
Thanks again for your help.
Shany