work one's fingers to the bone - 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.
Also, work one's tail or butt off. Exert oneself, labor very hard, as in She's working her fingers to the bone to support her children, or I work my tail off and then the government takes half my income in taxes. The first hyperbole, with its image of working the skin and flesh off one's fingers, dates from the mid-1800s; the less polite variants date from the first half of the 1900s.