There are quite a bit of wood residue left on inner rim after soundboard removal. We can use either sanding or teaming method to clean the inner rim surface. Use sanding when inside of outer rim is not going to be refinished. Use steam if it is going to be stripped and refinished. The first step of either method is to chisel the wood residue as clean as possible, leaving minimum amount of wood to be sanded or steamed off.
Before and after chisel cleaning.
This piano is going to be completely refinished. So steam is being used here. Line a few very wet rags on inner rim, steam for about a minute. The wood residue turns into a film and is easily taken off with a scraper.
Before and after cleaning. Note the steam lets water vapor go into old finish and makes it white. Only use steam when inside of the case is going to be refinished.