Boring Process and Types of Boring
– Boring is the process of enlarging a hole using a cutting tool or boring head.
– It achieves greater accuracy of the hole diameter and can cut tapered holes.
– Boring can be supported on both ends (lineboring) or reach through an existing hole (backboring).
– Boring is more challenging than turning due to toolholding rigidity and clearance angle requirements.
– Boring is a separate area of machining practice with its own tips, tricks, and challenges.
History, Applications, and Machine Tools Used
– The first boring machine tool was invented in 1775 by John Wilkinson.
– Boring and turning have counterparts in cylindrical grinding.
– Boring can be done on general-purpose machines like lathes or milling machines.
– Specialized machines like jig borers and boring mills are designed for primary boring functions.
– Boring is used in various industries for achieving precise dimensions and tolerances.
– Boring mills include vertical and horizontal boring mills.
Lathe Boring
– Lathe boring uses a cutting tool or boring head to enlarge existing openings.
– It can produce straight holes, tapered holes, and counterbores.
– The workpiece is held in the chuck and rotated while the cutting tool is fed into the hole.
Tolerances, Surface Finish, and Limitations of Boring
– Tolerances in lathe boring can range from ±0.010in to ±0.0005in.
– Surface finish in boring typically ranges from 8 to 250 microinches.
– Boring may not provide the required accuracy of form and size for some parts.
– Diameter variations, taper, roundness error, and cylindricity error may be unacceptable.
– Internal cylindrical grinding is often used for parts requiring higher accuracy.
Advancements in Machining Technology and Challenges with Workpiece Rigidity
– New grades of carbide and ceramic cutting inserts have increased accuracy and surface quality.
– These advancements have expanded the range of workpiece hardness values that can be worked on.
– Workpiece movement due to cutting or temperature changes can cause positional errors.
– Internal and external cylindrical grinding may be preferred over boring and turning in some cases.
– Engineers seek alternate workpiece materials and designs to address immobility issues. Source: https://en.wikipedia.org/wiki/Boring_(manufacturing)
In machining, boring is the process of enlarging a hole that has already been drilled (or cast) by means of a single-point cutting tool (or of a boring head containing several such tools), such as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters.
There are various types of boring. The boring bar may be supported on both ends (which only works if the existing hole is a through hole), or it may be supported at one end (which works for both, through holes and blind holes). Lineboring (line boring, line-boring) implies the former. Backboring (back boring, back-boring) is the process of reaching through an existing hole and then boring on the "back" side of the workpiece (relative to the machine headstock).
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 first boring machine tool was invented by John Wilkinson in 1775.
Boring and turning have abrasive counterparts in internal and external cylindrical grinding. Each process is chosen based on the requirements and parameter values of a particular application.
