ok, i solve my problem!
ipad is ipad...if you change or add font with calibre, the prog work correctly...and other ebook reader see any new font added...but not ipad! ipad work at one world apart...so, if you want see a new font add to your book on ipad, you must add one file called com.apple.ibooks.display-options.xml with this content:
<?xml version="1.0" encoding="UTF-8"?>
<display_options>
<platform name="*">
<option name="specified-fonts">true</option>
</platform>
</display_options>