Posted by Martin Connelly on 22/10/2018 19:35:36:
Boring bars are not hard steel and mark easily when clamped by screws acting directly on the surface. Since it is good practice to only have them protruding just enough they are frequently repositioned and the surface can get chewed up. A clamping system that avoids direct contact by rotating screws should be used. If you drill a block and slot one side then the tool post clamping screws will squeeze the block to clamp the bar and keep the bar in good condition. The clamping block can be cleaned up or replaced as it becomes necessary.
Martin C
I've got a couple of 5/16" and 3/8" diameter boring bars that take 1/8" and 3/16" square-section HSS bits. They have a straight transverse location at one end and a 45 deg angled one at t'other, and a slotted square-section sleeve of the sort Martin describes to mount them at whatever protrusion length will cut the required bore depth.
You can adjust cutting rake to some extent by rotating the bar in the sleeve, and when you clamp it it's held tight.
I've so far (about 18 years) always used the angled bit location, since that way the bit clears the bore or bottoms out before the bar does.
By taking off the sleeve and fitting a long bit you can stick it in the chuck and use it as a handy flycutter, too.
These two do all the boring and flycutting I've ever needed. I've had to replace one that I damaged a long time ago by severe overtightening, but apart from that I can't see me wanting anything else.
A good example in 16mm size is Ebay Item 302924490432 .