[van Dyck]

I've encountered the same problem with the Neway cutters: they do not cut concentric. The seats need touching up with a "stone".
The main thing with seat grinding equipment is the mandrel-to-pilot fit. If that fit is sloppy, you'll never get a good seat. I use Sioux equipment and find their stuff to be better quality to B&D, KOLee, and others of the 50s - 60s era.