The idea for the concave tool was to make some radius in the front of the piece, and with this one it's possible to go on a 5mm. radius, if I make a support with a recess it's possible to go to 1mm. theorically, it's not make for radius more than 30mm. the diameter of the cutting rod is too small on this model.
For bigger concave radius, I use the convex model with the head reversed under the center line.
Here is the completed page about Tripan tools, they are some others to photography when i've time…