Drilling Machine
Drilling is the cutting process of using a drill bit in a drill to cut or enlarge holes in solid materials, such as wood or metal. Different tools and methods are used for drilling depending on the type of material, the size of the hole, the number of holes, and the time to complete the operation.
Drilling is a cutting process in which a hole is originated or enlarged by means of a multipoint, fluted, end cutting tool. As the drill is rotated and advanced into the workpiece, material is removed in the form of chips that move along the fluted shank of the drill. One study showed that drilling accounts for nearly 90% of all chips produced.
Process Characteristics
-Cutting tools or workpieces are rotated relative to each other.
-Creates or enlarges holes.
-Generates small burrs upon entry and more coarse burrs upon exit of the workpiece.
-Uses a multi-point rotating, fluted, end cutting tool (drill).
-May produce coarse, helical feed marks, depending on machining parameters (feed, speed, tool geometry, coolant, etc.)
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. This causes the workpiece to become more susceptible to corrosion at the stressed surface.
Process Schematic
Drilling involves relative axial and rotations between the drill and the workpiece. Usually, the drill rotates and proceeds into the workpiece, but sometimes the opposite is true. Chips are removed by following along grooves of flutes in the drill. Although long spiral chips usually result from drilling,adjustment of the feed rate can result in chips with a range of many different shapes and sizes. Material of workpiece can also chane the range of different chip shapes and sizes.
Workpiece Geometry
A drilled hole may be distinguished from one produced by piercing, casting, molding, torch cutting, etc. by the presence of helical feed marks inside the hole and small burrs on the workpiece as the drill enters and exits. Drilled holes are usually sharp around the edge where the drill has entered the workpiece.
Machining operations for drilling
Some of the basic drilling operations are:
a) Reaming - to provide better tolerance of its diameter and to improve surface finish.
b) Tapping - to provide internal screw threads on an existing hole.
c) Counterboring - to provide a step hole in which a larger diameter follows a smaller diameter partially into a hole.
d) Countersinking - similar to counterboring but the step in the hole is cone-shaped.
e) Centering - creating a hole to accurately establish its location for subsequent drilling.
f) Spotfacing - similar to milling where it is used to provide a flat machined surface on the workpiece in the localized area.
Tool Style
Different jobs require different types of drills, that is why there are so many different drill types in many different shapes and sizes. Countersink or center drills are mainly used to center holes very accurately. A more common drill is the twist drill, a drill that produces a majority of drilled holes. Some specialty drills include subland, spade, and indexable drills.
Toolholding Methods
Drills are either straight shank or taper shank. Straight shank drills are often held in a keyless chuck for quick load/unload time. Tapered shank drills are held in the female Morris taper in the end of the machine tool spindle. Removal of the drill is accomplished by driving a tapered drift through a hole in the spindle and against the end of the drill's tang.
Workpieces
A drilled hole can be distinguished from piercing, casting, molding, and torch cutting. Drilled holes are usually sharp around where the drill entered the workpiece. The different pieces that can be used are rods, plates, castings, extruded, and more.
Drilling in metal
Under normal usage, swarf is carried up and away from the tip of the drill bit by the fluting of the drill bit. The continued production of chips from the cutting edges produces more chips which continue the movement of the chips outwards from the hole. This continues until the chips pack too tightly, either because of deeper than normal holes or insufficient backing off (removing the drill slightly or totally from the hole while drilling). Lubricants and coolants (i.e. cutting fluid) are sometimes used to ease this problem and to prolong the tools life by cooling and lubricating the tip and chip flow. Coolant is introduced via holes through the drill shank (see gun drill). When cutting aluminum in particular, cutting fluid helps ensure a smooth and accurate hole while preventing the metal from grabbing the drill bit in the process of drilling the hole. Only a few drops are needed at a time.
Straight fluting is used for copper or brass, as this exhibits less tendency to "dig in" or grab the material. If a helical drill (twist drill) is used then the same effect can be achieved by stoning a small flat parallel with the axis of the drill bit.
For heavy feeds and comparatively deep holes oil-hole drills can be used, with a lubricant pumped to the drill head through a small hole in the bit and flowing out along the fluting. A conventional drill press arrangement can be used in oil-hole drilling, but it is more commonly seen in automatic drilling machinery in which it is the workpiece that rotates rather than the drill bit.
* Peck Increments: If a peck cycle is needed while drilling a deep hole, the peck increment should not exceed 1/2 the diameter of the drill.
Machinability Ratings
Aluminum - good to excellent
Brass - good to excellent
Cast Iron - fair to good
Mild Steel - fair to good
Stainless Steel - poor to fair
Plastics - good to excellent
Drilling in wood
Wood being softer than most metals, drilling in wood is considerably easier and faster than drilling in metal. Cutting fluids are not used or needed. The main issue in drilling wood is assuring clean entry and exit holes and preventing burning. Avoiding burning is a question of using sharp bits and the appropriate cutting speed. Drill bits can tear out chips of wood around the top and bottom of the hole and this is undesirable in fine woodworking applications.
The ubiquitous twist drill bits used in metalworking also work well in wood, but they tend to chip wood out at the entry and exit of the hole. In some cases, as in rough holes for carpentry, the quality of the hole does not matter, and a number of bits for fast cutting in wood exist, including spade bits and self-feeding auger bits. Many types of specialised drill bits for boring clean holes in wood have been developed, including brad-point bits, Forstner bits and hole saws. Chipping on exit can be minimized by using a piece of wood as backing behind the work piece, and the same technique is sometimes used to keep the hole entry neat.
Holes are easier to start in wood as the drill bit can be accurately positioned by pushing it into the wood and creating a dimple. The bit will thus have little tendency to wander. In metal working, an accurate position needs to be marked with a punch to avoid the bit wandering from the desired position of the hole.
Drilling in stone
When drilling in stone, one must pay particular attention to th type of stone he drills into. There are three different classifications of drill bits used for drilling into stone: soft, medium, and hard. Soft formation rock bits are used in unconsolidated sands, clays, and soft limestones, and red beds, etc. Medium formation bits are used in calcites, dolomites, limestones, and hard shale, while hard formation bits are used in hard shale, calcites, mudstones, cherty lime stones and hard and abrasive formations.
Drilling is the cutting process of using a drill bit in a drill to cut or enlarge holes in solid materials, such as wood or metal. Different tools and methods are used for drilling depending on the type of material, the size of the hole, the number of holes, and the time to complete the operation.
Drilling is a cutting process in which a hole is originated or enlarged by means of a multipoint, fluted, end cutting tool. As the drill is rotated and advanced into the workpiece, material is removed in the form of chips that move along the fluted shank of the drill. One study showed that drilling accounts for nearly 90% of all chips produced.
Process Characteristics
-Cutting tools or workpieces are rotated relative to each other.
-Creates or enlarges holes.
-Generates small burrs upon entry and more coarse burrs upon exit of the workpiece.
-Uses a multi-point rotating, fluted, end cutting tool (drill).
-May produce coarse, helical feed marks, depending on machining parameters (feed, speed, tool geometry, coolant, etc.)
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. This causes the workpiece to become more susceptible to corrosion at the stressed surface.
Process Schematic
Drilling involves relative axial and rotations between the drill and the workpiece. Usually, the drill rotates and proceeds into the workpiece, but sometimes the opposite is true. Chips are removed by following along grooves of flutes in the drill. Although long spiral chips usually result from drilling,adjustment of the feed rate can result in chips with a range of many different shapes and sizes. Material of workpiece can also chane the range of different chip shapes and sizes.
Workpiece Geometry
A drilled hole may be distinguished from one produced by piercing, casting, molding, torch cutting, etc. by the presence of helical feed marks inside the hole and small burrs on the workpiece as the drill enters and exits. Drilled holes are usually sharp around the edge where the drill has entered the workpiece.
Machining operations for drilling
Some of the basic drilling operations are:
a) Reaming - to provide better tolerance of its diameter and to improve surface finish.
b) Tapping - to provide internal screw threads on an existing hole.
c) Counterboring - to provide a step hole in which a larger diameter follows a smaller diameter partially into a hole.
d) Countersinking - similar to counterboring but the step in the hole is cone-shaped.
e) Centering - creating a hole to accurately establish its location for subsequent drilling.
f) Spotfacing - similar to milling where it is used to provide a flat machined surface on the workpiece in the localized area.
Tool Style
Different jobs require different types of drills, that is why there are so many different drill types in many different shapes and sizes. Countersink or center drills are mainly used to center holes very accurately. A more common drill is the twist drill, a drill that produces a majority of drilled holes. Some specialty drills include subland, spade, and indexable drills.
Toolholding Methods
Drills are either straight shank or taper shank. Straight shank drills are often held in a keyless chuck for quick load/unload time. Tapered shank drills are held in the female Morris taper in the end of the machine tool spindle. Removal of the drill is accomplished by driving a tapered drift through a hole in the spindle and against the end of the drill's tang.
Workpieces
A drilled hole can be distinguished from piercing, casting, molding, and torch cutting. Drilled holes are usually sharp around where the drill entered the workpiece. The different pieces that can be used are rods, plates, castings, extruded, and more.
Drilling in metal
Under normal usage, swarf is carried up and away from the tip of the drill bit by the fluting of the drill bit. The continued production of chips from the cutting edges produces more chips which continue the movement of the chips outwards from the hole. This continues until the chips pack too tightly, either because of deeper than normal holes or insufficient backing off (removing the drill slightly or totally from the hole while drilling). Lubricants and coolants (i.e. cutting fluid) are sometimes used to ease this problem and to prolong the tools life by cooling and lubricating the tip and chip flow. Coolant is introduced via holes through the drill shank (see gun drill). When cutting aluminum in particular, cutting fluid helps ensure a smooth and accurate hole while preventing the metal from grabbing the drill bit in the process of drilling the hole. Only a few drops are needed at a time.
Straight fluting is used for copper or brass, as this exhibits less tendency to "dig in" or grab the material. If a helical drill (twist drill) is used then the same effect can be achieved by stoning a small flat parallel with the axis of the drill bit.
For heavy feeds and comparatively deep holes oil-hole drills can be used, with a lubricant pumped to the drill head through a small hole in the bit and flowing out along the fluting. A conventional drill press arrangement can be used in oil-hole drilling, but it is more commonly seen in automatic drilling machinery in which it is the workpiece that rotates rather than the drill bit.
* Peck Increments: If a peck cycle is needed while drilling a deep hole, the peck increment should not exceed 1/2 the diameter of the drill.
Machinability Ratings
Aluminum - good to excellent
Brass - good to excellent
Cast Iron - fair to good
Mild Steel - fair to good
Stainless Steel - poor to fair
Plastics - good to excellent
Drilling in wood
Wood being softer than most metals, drilling in wood is considerably easier and faster than drilling in metal. Cutting fluids are not used or needed. The main issue in drilling wood is assuring clean entry and exit holes and preventing burning. Avoiding burning is a question of using sharp bits and the appropriate cutting speed. Drill bits can tear out chips of wood around the top and bottom of the hole and this is undesirable in fine woodworking applications.
The ubiquitous twist drill bits used in metalworking also work well in wood, but they tend to chip wood out at the entry and exit of the hole. In some cases, as in rough holes for carpentry, the quality of the hole does not matter, and a number of bits for fast cutting in wood exist, including spade bits and self-feeding auger bits. Many types of specialised drill bits for boring clean holes in wood have been developed, including brad-point bits, Forstner bits and hole saws. Chipping on exit can be minimized by using a piece of wood as backing behind the work piece, and the same technique is sometimes used to keep the hole entry neat.
Holes are easier to start in wood as the drill bit can be accurately positioned by pushing it into the wood and creating a dimple. The bit will thus have little tendency to wander. In metal working, an accurate position needs to be marked with a punch to avoid the bit wandering from the desired position of the hole.
Drilling in stone
When drilling in stone, one must pay particular attention to th type of stone he drills into. There are three different classifications of drill bits used for drilling into stone: soft, medium, and hard. Soft formation rock bits are used in unconsolidated sands, clays, and soft limestones, and red beds, etc. Medium formation bits are used in calcites, dolomites, limestones, and hard shale, while hard formation bits are used in hard shale, calcites, mudstones, cherty lime stones and hard and abrasive formations.
Tool Geometry
| MATERIAL | Point Angle | Helix Angle | Lip Relief Angle |
| Aluminum | 90 to 135 | 32 to 48 | 12 to 26 |
| Brass | 90 to 118 | 0 to 20 | 12 to 26 |
| Cast Iron | 90 to 118 | 24 to 32 | 7 to 20 |
| Mild Steel | 118 to 135 | 24 to 32 | 7 to 24 |
| Stainless Steel | 118 to 135 | 24 to 32 | 7 to 24 |
| Plastics | 60 to 90 | 0 to 20 | 12 to 26 |
Time Calculations
When calculating the time needed to drill. use these formulas.
Cutting Time: L/F
Retract Time: L/T
Positioning TIme: H(S/R)
rpm: 4xv/D
Feed Rate: FxNxrpm
D = Diameter of tool
A = Approach time
O = Over-travel
F = Feed rate
V = Cutting Speed
r = Retract rate
H = Number of Holes
S = Distance to next Hole
R = Rapid travel
f = Feed per tooth
N = Number of teeth
L = Length of cut
d = Depth of Hole
Cost Elements
Cost elements include the following:
* setup time.
* load/unload time.
* Idle time.
* Cutting time.
* Tool costs.
* Direct labor rate.
* Overhead rate.
* Amortization of equipment and tooling
Source:wikipidea.org
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