My sister just had a hammer snap off on her piano and doesn’t know what to do. Can you advise?
The best advice is to call in your piano tuner / technician. This is not something that can be successfully repaired with enthusiastic DIY. The broken hammer shank has to be carefully drilled or drawn out of the hammer head and butt portions and a new shank inserted and glued at the correct rake angle and alignment to the string. If you have retrieved the old shank with the hammer head still attached from the bottom of the piano, please do not throw it away or lose it! If a head from a different set has to be used there will be a noticeable difference in tone between it and the other hammers. Hammer shanks used to be made from cedar which gets brittle with age, and is possibly why your hammer broke. Modern shanks (what yours will be replaced with) are sycamore which has a good straight grain and is much stronger.