I have a Myford and a Cummins mini-lathe and saw on John Moran's site  his mini-lathe version of your ball/radius turning attachment for your 9x20. I made one like his for the mini-lathe and, after viewing your site, decided I could modify it more like yours and use it on both the Myford and the mini-lathe. I've made your modification (two cutting inserts) to allow easier concave turning and have bolted a small piece of 0.5" wide ruler to the tool holder to allow setting of the radius by 1/64 inch increments. I can turn a ball 2" OD. It works great and the addition of the ruler makes it easy to set radius.