Why does this need to be done?
When the hammer with a large groove strikes the sting, the inertia energy from the hammer is spread through the surface of contact. At the bottom of the groove, there will be a lot of surface contact, unlike a properly shaped hammer that has more of a point to it. Also, when the strings vibrate after the hammer strikes, the strings can rub on the felt inside the groove while the hammer is pulling back. This can cause a whining sound.
If a piano hasn’t been maintained for over a decade and the tuning is very far from pitch, we recommend this maintenance before performing a pitch raise. This helps the strings not break nearly as frequently as we stretch the strings to pitch. The hammer is more gentle to the string when it has an egg shaped point.
After the hammers are reshaped, there needs to be adjustments to your piano to compensate for the loss of felt. Also, since this job creates a tremendous amount of dust in the action, a thorough cleaning of the action is required. This adjustment and cleaning are included in our service.
Please understand that when a significant amount of felt is removed, weight of the action can change. Also, tone can change depending on the density of the felt at the new layer. If this will challenge your preference, then hammer replacement will be the solution.