work one's fingers to the bone
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.