WHAT IS BORING?
Boring, in the broadest sense of the term, is an operation that can be
performed by almost any machine tool with a rotating spindle and a feed motion,
and most of them (excluding grinders) do perform boring of one sort or another.
But boring is also a specialized operation and often involves
requirements that are best met by machines designed specifically for boring.
This specialization has proceeded along several broad, general lines, and the
requirements include such varied factors as precision, workpiece size,
versatility, and high productivity.
Therefore, the machines known as boring machines are quite a
mixed group. In fact, about the only thing they all have in common is that their
primary purpose, or at least one of their primary purposes, is to perform
First, though, let's analyze boring in general, so that all
boring is included. Then we can zero in on the operations that are performed on
the various boring machines themselves.
Boring can be defined as the machining of an internal surface
under three conditions, all of which must be met:
(1) with a single-point cutting tool.
(2) with either the cutting or the workpiece rotating about
the axis of the surface being machined, and
(3) with a feed relationship between the workpiece and the
tool in a direction parallel to the surface being machined.
Actually, it is not uncommon to see a two-cutter boring tool,
but the essential factor is that these tools could still do their work, even if
they had only one cutting edge. Drilling, reaming, and tapping do not meet this
requirement and are not included in boring. Milling is out because the cutter
does not rotate about the axis of the surface being machined.
Precision was not mentioned in the definition of boring
because it is not a basic requirement. However, in common usage, boring usually
implies work within fairly close limits-accurate diameters, most important,
true, straight holes. In fact, this is often the reason why boring is performed
in stead of drilling.
In the range of bole sizes that can be finished by either
drilling or boring, drilling is more economical, and boring is done only if the
quality of the product demands it.