nose to the grindstone, keep one's - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Stay hard at work, as in We expect John to get good grades again, since he really keeps his nose to the grindstone. This expression, first recorded in 1539, alludes to a tool that must be sharpened by being held to a grindstone.