Difference between boring and boring/facing head ?

Hi
I see some boring heads advertised as boring and facing heads - whats the difference ?
thanks Tim

  Quoted Text Here  
Wild guess. Could some heads only have tool mounting holes in the Periphery whilst others have those holes in both the Face and Periphery?

Tim Nash (aka TMN) wrote:
  Quoted Text Here  
Without wanting to sound a smart arse a boring head can only bore a hole whereas a boring & facing head can also face a flange. Essentially there's a mechanism that causes the boring tool to edge out slightly every revolution when requires so that a flange could be both bored parallel and faced up true.
Boring & facing heads usually have a knurled ring around the body.
Charles

Tim Nash (aka TMN) wrote:
  Quoted Text Here  
If the cutting tool only sticks out at the side of the head then it can only bore. If it sticks out at an angle that's adjustable for diameter while also always being below the bottom surface of the head then it can both bore and face. A true flycutter by contrast has a tool that only sticks out below the head and not outwith its periphery so that can only face.
The advantage of a single purpose boring head is if the tool adjustment is perpendicular to the bore it can be easily and accurately adjusted for cutting diameter with a micrometer attachment. A tool moving in and out at an angle can also face but is harder to set up for boring. You either need to take trigonometry into account or have a more complex registering and setting system. A true flycutter can be adjusted for diameter without losing rigidity whereas a boring and facing head loses rigidity as the tool protrudes more. Every compromise has its downsides. Horses for courses.
For high precision boring such as for engine blocks you'd always use a single purpose boring head. For high precision skimming you'd ideally use a single purpose flycutter. For roughing out material in either mode you have your compromise boring/facing head.

  Quoted Text Here  
Some confusion here, I think. What most people think of as a boring & facing head is strictly a boring and *automatic* facing head, such as the Wohlhaupter. See http://www.wohlhaupter.de/daten/Kataloge/UPA_Englisch1200.pdf
for what they can do.
Tim

  Quoted Text Here  
This seems to be typical "theirs" vs "ours" !!!

  Quoted Text Here  
Dave - So a boring head that model engineers generally use that can take the cutter at 90 degrees to the shank or facing down parallel to the shank is a boring/facing head?
thanks tim