The trimming stand is homemade by shop owner. The action stack is screwed down, then raised to an angle to be easily worked on. Use a clamp to fasten one section of hammer shanks so they won't move everywhere during trimming process. Lift this section with a block. Also protect hammer felt with tape or plastic wrap.
Wear mask(s), safety glasses, and ear protection. Use a dremel with a grinding wheel attached. Carefully cut off the over hang shank without digging into neighboring hammer tails or hammer felt. Remove tape or plastic wrap, even out the hammer tails with a belt sander. Be careful not to over shape or sanding too much wood off.
Lightly sand off splinters and sharp edges on hammers. Vacuum clean then use compressed air to remove any dust from hammer felt. The composite dust from shanks is very fine. The compressed air helps with it better than vacuum.
Did my dirty gloves pollute the hammers again...?