Is it possible your lathe requires a specific number on the thread dial to do 10 tpi? Also check the change gear setup again. If it is running the wrong ratio it might mess it up. Try locking the compound and use the cross slide to adjust your cut. Try cutting .005" at a time. Is your chuck secure in reverse, or won't unscrew under load? If so try mounting the cutter upside down and cut from the shoulder out. Remember the feed works opposite in reverse so run it in air to test it first.
Dave
Dave