only too...to do sth 等于 rather ,very ,quite
例句：I am only too glad to help you.我很高兴能帮助你.I am only too glad to go.我很高兴能去.
补充：only too...to do sth是一个句型,它的意思与rather,much,very都一样的,用来修饰形容词,表达很怎么样,非常怎么样,极其怎么样.比如我非常乐意能帮到你的忙.I am only too glad to help you .它就等于I am very glad to help you.
加not,but,all,never都是进一层的修饰,用以表达更强烈的感情.比如I am only never too glad to know you.认识你我再高兴不过了.
括号里面的not,all,never,but都是用以修饰的,加强语气肯定或否定.你可以不带这些词,直接用only too...to do sth,也可以加上这些修饰的词,以加强感情的表达.