Boring (manufacturing)
Because of the limitations on tooling design imposed by the fact that the workpiece mostly surrounds the tool, boring is inherently somewhat more challenging than turning, in terms of decreased toolholding rigidity, increased clearance angle requirements (limiting the amount of support that can be given to the cutting edge), and difficulty of inspection of the resulting surface (size, form, surface roughness).
These are the reasons why boring is viewed as an area of machining practice in its own right, separate from turning, with its own tips, tricks, challenges, and body of expertise, despite the fact that they are in some ways identical.
The dimensions between the piece and the tool bit can be changed about two axes to cut both vertically and horizontally into the internal surface.
A tapered hole can be made by simultaneously feeding the cutting edge in both the radial and axial directions.
First developed to make the barrels of firearms and artillery, these machining techniques find wide use today for manufacturing in many industries.
Geometries ranging from simple to extremely complex in a variety of diameters can be produced using boring applications.
To produce a taper, the tool may be fed at an angle to the axis of rotation or both feed and axial motions may be concurrent.
Straight holes and counterbores are produced by moving the tool parallel to the axis of workpiece rotation.
On these chucks the runout faces limitations; on late-model CNCs, it can be quite low if all conditions are excellent, but traditionally it is usually at least .001-.003 in (0.025-0.075 mm).
In some cases tolerances as tight as ±0.0001 in (±0.0038 mm) can be held in shallow holes, but it is expensive, with 100% inspection and loss of nonconforming parts adding to the cost.
Often a part will be roughed and semifinished in the machining operation, then heat treated, and finally, finished by internal cylindrical grinding.
The limitations of boring in terms of its geometric accuracy (form, position) and the hardness of the workpiece have been shrinking in recent decades as machining technology continues to advance.
However, working to tolerances of only a few micrometres (a few tenths) forces the manufacturing process to rationally confront, and compensate for, the fact that no actual workpiece is ideally rigid and immobile.
It is factors such as these that sometimes preclude finishing by boring and turning as opposed to internal and external cylindrical grinding.
When engineers are confronted with such a case, it drives the quest to find other workpiece materials, or alternate designs that avoid relying so heavily on the immobility of part features on the micro or nano scales.
