plug away
peg away
slog
keep one's nose to the grindstone
keep one's shoulder to the wheel

I'd get up pretty late mornings and peg away at my Spanish books.

They pegged away in silence for some time.

The only thing is to peg away.

I see you pegging away at your books, no, I mean studying hard.

If I peg away for some weeks without a break I am safe.

He pegs away obsessively at his barn, generally locating it off-center.

They couldn't mean a police car, for they weren't accompanied by a siren, nor were guns pegging away.

He didn't argue, just stepped up close to the other vamp and started pegging away at it.

Such a much more attractive way of earning a living thaOn just pegging away at a job.

I keep pegging away, but it don't seem to do much good;" and Dan looked discouraged.