Drilling

The bit is pressed against the work-piece and rotated at rates from hundreds to thousands of revolutions per minute.

In rock drilling, the hole is usually not made through a circular cutting motion, though the bit is usually rotated.

[2] Drilling may affect the mechanical properties of the workpiece by creating low residual stresses around the hole opening and a very thin layer of highly stressed and disturbed material on the newly formed surface.

Chips may form long spirals or small flakes, depending on the material, and process parameters.

This minimizes the drill bit's tendency to "walk", that is, to be deflected from the intended center-line of the bore, causing the hole to be misplaced.

The tendency to walk is also preempted in various other ways, which include: Surface finish produced by drilling may range from 32 to 500 microinches.

Application of these fluids is usually done by flooding the workpiece with coolant and lubricant or by applying a spray mist.

Using methods such as a rotating tool and counter-rotating workpiece are common techniques to achieve required straightness tolerances.

A high tech monitoring system is used to control force, torque, vibrations, and acoustic emission.

The key feature of gun drilling is that the bits are self-centering; this is what allows for such deep accurate holes.

Trepanning is commonly used for creating larger diameter holes (up to 915 mm (36.0 in)) where a standard drill bit is not feasible or economical.

Trepanning removes the desired diameter by cutting out a solid disk similar to the workings of a drafting compass.

Trepanning is performed on flat products such as sheet metal, granite (curling stone), plates, or structural members like I-beams.

High spindle speeds that exceed 10,000 RPM also require the use of balanced tool holders.

The main principle consists in axial vibrations or oscillations in addition to the feed movement of the drill so that the chips break up and are then easily removed from the cutting zone.

Circle interpolating, also known as orbital drilling, is a process for creating holes using machine cutters.

The lower thrust force results in a burr-less hole when drilling in metals.

Cutting fluid is sometimes used to ease this problem and to prolong the tool's life by cooling and lubricating the tip and chip flow.

When cutting brass, and other soft metals that can grab the drill bit and causes "chatter", a face of approx.

This process is faster, but is only used in moderately long holes, otherwise it will overheat the drill bit.

The main issue in drilling wood is ensuring clean entry and exit holes and preventing burning.

Drill bits can tear out chips of wood around the top and bottom of the hole and this is undesirable in fine woodworking applications.

Some materials like plastics as well as other non-metals and some metals have a tendency to heat up enough to expand making the hole smaller than desired.