Verified answer

"だけ" is simply translated into "only" or "just". "ばかり" is more complicated. It has many meanings and nuances.

私はスシだけ食べる > I only eat sushi.(I don't eat anything else.)

私はスシばかり食べる > I eat sushi (more than I should eat.) (I might eat something else, but it is not enough.) > I always eat sushi.

オレンジを三つだけ買った > I bought just 3 oranges. (not 2, not 4, I bought 3 oranges)

オレンジを三つばかり買った > I bought about 3 oranges. (it might be 2 or 4)

来ただけだ > I only came here. (I did nothing else)

来たばかりだ > I've just came here. (I have no time to do anything else)

For example,

仕事だけが人生じゃない (both written & colloquial)

仕事ばかりが人生じゃない(more like written)　

--> 仕事ばっかり（ばっか）が人生じゃない(colloquial)

Although most of the time だけ can be replaced with ばかり（ばっかり・ばっか）

the following, for example, is NOT substitutable:

（person）だけに verb 　e.g. これ、君だけにあげる (I only give you this.)

We don't say 君ばかりにあげる

Or,　君ばかりがもらう sounds more jealous than 君だけがもらう

(the both mean "only you'll have that.")

-- so far...

one more example;

You can say ～だけ？ alone. e.g. 俺だけ？　　え？これだけ？ 　 休みは土曜日だけ？

But you cannot say 　～ばかり（ばっかり／ ばっか）？ you need a PARTICLE

～ばかりが...、　～ばかりで...、　～ばかりを...　etc.

毎日勉強ばっかり～ with no question mark (I just stury and study everyday!) is OK.

to me nothing it looks exactly the same