Boring heads for the mill

[Hopefuldave]

Choosing between 2" and 3"... I guess it comes down to how big you think you'll want to go! The rigidity's likely to be limited by the size of the shank / spindle and overall construction quality more than the head size, although a longer dovetail will always be more rigid than a shorter? I'd advise going for a dovetail / leadscrew type rather than a pivoting-arm, purely because the leadscrew makes it a lot easier to adjust to dimension.

Re your press fit - if this is for a 15mm shaft, and it actually *is* 15.00 mm, you're a touch on the loose side - .590" would be a press fit (14.986mm, 0.55thou" undersize), .591 would be a "close sliding" fit, at 15.011mm (about 0.45 thou" clearance) - shoot for 0.590" and then lap the bore if you need to?

Just my ha'pennorth,
Dave H. (the other one)