Unfortunately, I couldn't find a direct link to a free PDF of the book. However, I can suggest some alternatives:
Google Drive Archive: Some academic communities maintain digital copies for educational use, such as this Principles of Machine Tools PDF Archive.
As for the availability of the book in PDF format, I couldn't find any direct links to download a free PDF copy of "Principles of Machine Tools" by A. Bhattacharya and G.C. Sen. However, you can try searching for the book on various online platforms, such as: