I have been contemplating building a bowl coring tool. My original thought was to make something like the Mcnaughton tool. However, I came across a video on youtube that might be of interest. It's noting like the Mcnaughton tool, but it is very nice. Take a look at it and let me know what you think:
It looks fairly easy to make if you can bend metal. It looks like both the cutting blade and the support underneath are the same ark. I think that they are simply 1/4's of a circle.