Radius turner from boring bar

What tap was used for the insert screw?
 
@Aukai it's M2.5x.45

Picked up an inexpensive set on Amazon: amazon.com/gp/product/B07DPRVSCR
 
Thank you I'm not up on metrics, just checking.
 
One other change that I forgot to mention. Not sure why they are designed this way, but the adjustment screw for the boring head only has a hex on one end, which in this application means that it's on either the bottom or on the chuck side as you use it.

This is fine as long as you're just rounding off the end of a rod. You can just set the cutter to the top of the rod, then work your way in making passes along the z-axis. But if you're trying for a ball, you need to change the diameter of the cutting arc as you work.

The solution is to remove the adjustment screw from the boring head, drill and tap the blind end, and loctite a grub screw into it so you can adjust the head from either side.

IMG_20200331_105955.jpg
 
Could you have removed the bottom piece and just reversed it? It seems you could just disassemble it and turn it around, right?
 
@r3292c as mentioned above, in a smaller lathe a standard boring bar holder forces the boring head too close to the centerline of the lathe, even withe the cross slide full retracted, leaving zero clearance between the boring head and the work. That's the reason for the offset rectangular mount for the body of this design.
 
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