If I only had one machine, I'd be very hesitant. Even with more, I'd be selective about which one I let someone borrow. That being said, I 'stole' my friend's machine once. She was on vacation and I was in the middle of a lace wedding dress and my machine quit. A friend loaned me hers, it wouldn't sew the lace so I broke into my close friend's house and took her precious Elna - the twin to mine. I did leave her a note. I hope she knew it was safe with me as I was the one who maintained it for her. We still laugh about it 30 years later, so I guess I was forgiven.