The ones used on a pole lathe are subject to less stress, probably why he (Robin) quoted me a big price to make one. I actually have an old ring tool, could grind the back off and see if it works wearing full safety gear to do so LOL. Seriously it is worth a go. Just as a pont of interest, the japanese ones seem to be backwards as they turn bowls on the far side, the upstroke as it were in the videos I have seen. If I had the know how I would consider making one but I am about as ignorant as is possible regarding metal work.
Pete