How do you replace the 10" grinding stone??? I can not get the old stone off the shaft.
Welcome to the forum, Rodger. The two most essential ingredients to removing a stuck grinding wheel are plenty of patience and plenty of penetrating oil. If that does not work after a day or two:
If you remove the leather honing wheel and the drive wheel, you can remove the grinding wheel and shaft through the grinding wheel end.
Once the shaft and grinding wheel are loose, you can increase your leverage by using Vise Grips or a pipe wrench on the shaft and a long 19mm or 3/4" wrench, preferably a box end wrench or a socket, on the nut.
If your shaft is an older non stainless steel model and rusted, this is an excellent opportunity to upgrade to a new stainless EZYlock shaft.
Whichever shaft you use, clean and regrease the nylon bushings.
Ken