A drill bit or drilling tool , when used in a drilling machine and drill bit, is a tool that can be produced with the spinning movement of holes in the solid material. There is a cutting tool for manufacturing of holes by the method of drilling . Drills only have cutting edges at their tips. During processing, they rotate around their own axis and penetrate the material along this axis. There are drills for working on wood , metal , plastic and stone .
The most common drilling tool, which makes up about a quarter of all cutting tools, is the twist drill . Most are made of high speed steel (HSS); For special applications there are also some that consist entirely or only partially on the cutting edges of hard metal , boron nitride or diamond . Besides the usual twist drills there are drills with indexable inserts for larger holes in steel, core drill for core drilling, centering on centering and gun drill for deep drilling . Removing the chips is problematic when drilling deep holes , which is why deep hole drills pump cooling lubricant into the hole under high pressure . A distinction is made between three types: ejector drill , BTA drill and single-lip drill . Countersink are actually for the lowering thought a similar drilling method for precision machining, but you also can drilling be used.
In contrast to the drill, a milling tool also rotates around its own axis, but is usually moved perpendicular or at an angle to the axis of rotation. Milling tools have cutting edges on their circumference. Some milling cutters are also conditionally suitable for drilling, but cannot or only insufficiently convey the chips out of the hole being created.
The drilling is a very old technique. Stone drills already appear in the older Upper Palaeolithic , the Aurignacian . At that time they were used to pierce softer materials such as wood, antlers or bones as well as hides. The distinction between Upper Paleolithic drills and so-called tines is difficult, however. Depending on the intended use, there were even then simple drills, heavy coarse drills, fine drills and long drills. Stone drilling techniques using quartz sand, for example in pearl production, were still relatively rare.
In the Mesolithic and Neolithic , more effective stone drilling techniques were developed, and the drilling technique is considered to be one of the important technical characteristics of that era that began around 10,000 years ago. They used this geschäftete drill bits and also quartz sand, which was also used for stone grinding, the other major technical innovation of the Neolithic period outside the purely agricultural technology and ceramics. The bow drill, also used to generate fire, was common. Both full-hole drills and hollow drills made of organic material were used (such as reeds), in which the drilling sand was contained in the sleeve and came out during drilling.
Typical palaeolithic drill from Gravettia approx. 28,000 to 22,000 years ago.
Cannon boring machine from the Diderot encyclopedia . The cannon hangs in the middle with the muzzle down so that the chips can fall out. Below is a göpel to drive.
Prehistoric drilling technique: There were two basic methods here:
- the fake hole , where picking on both sides created hourglass-shaped depressions that left a double hole,
- the real hole as a full or hollow hole (tenon hole ) and lens hole .
The full drilling was carried out with a rapidly rotating drill head made of hard material, possibly with the help of sand as emery. The hallmark is the V-shaped borehole.
For hollow drilling , hollow wood, hollow bones or reeds are used as a rapidly rotating drilling aid, with the actual grinding work being done using quartz sand that is piled up around the drill. Usually drilling is done from two sides. One-sided drilling creates a conical pin that falls out. The technique is less time consuming than full drilling.
The lens hole of the Natufian is a special case, because it was only used for the erosion of stone vessels using a bow drill.
In ancient times , the auger bits were used for drilling , which consisted of a twisted square rod and only provided sawdust, but no chips. It was replaced by the spoon drill , which was in use until the 19th century. For the processing of glass and precious stones, drills were also used, the tips of which were set with diamond fragments.
In the early modern period , cannons were first cast from bronze over a core and then drilled out . For this purpose, vertical or horizontal boring mills were developed. Later it was also possible to drill iron cannon barrels from solid pieces.
In the middle of the 19th century, the twist drill that is still in use today , also known as the spiral drill, was created. As it is difficult to manufacture, it did not gain acceptance until the end of the century.
A drill consists of a shaft and a head. The drill shank transmits the torque to the drill head, guides the drill head, enables the cuttings to drain and ensures the supply of a cooling lubricant. The drill head takes over the machining work.
The drill bit is held by its shank (often cylindrical , normally 0.5 - 13 mm, sometimes also a hexagon ) in a tool holder, which is usually designed as a drill chuck , and thus connected to a drill . Diameters from 5 mm can also be provided with a conical seat, the so-called Morse taper (e.g. MK1, MK2 etc.). Drills from 13 mm usually only have MK shanks, so that the necessary high torque of the drill can be transmitted better. (see also drill chuck)
The drill head of the normal twist drill consists of the tip, the two cutting edges and the secondary cutting edge connecting the two cutting edges. The point angle is usually 118 ° (100 ° for aluminum and copper, up to 135 ° for hardened steel). The two main cutting edges each remove a chip from the material to be processed . Depending on the material to be processed, the cutting edges are ground at suitable angles ( cutting angle , clearance angle , rake angle , wedge angle ). The chips are guided out of the resulting borehole against the feed direction through lateral, helically worked grooves on the shaft , which act as chip chambers .
A wood drill bit is characterized by the fact that it has a thin tip in the middle for centering. The two cutting edges protrude so that the edge of the hole is cut first. This will cleanly cut the fibers of the wood and give the hole a relatively smooth edge. Wood drills are usually made of a chrome - vanadium alloy and some are also carbide-tipped.
The wood drills include the Forstner bit, the artificial drill / cylinder head drill, the nail drill, the drill saw and the auger bit.
Twist drills, twist drills or spiral groove drills have a conical head and almost always two cutting edges, each consisting of a main cutting edge, secondary cutting edge and cross cutting edge. They are the most frequently used cutting tools with a share of 20 to 25%.
Center drill and center drill
A center drill is a drill specially designed for the production of center bores. It is made of HSS , is particularly short and has a stepped profile. This has an additional center point at the very front. The diameter of this tip is also the nominal diameter of the center drill. It is 0.5–12.5 mm and is constant over a length that is slightly larger than the respective diameter value. Then the cutting edges merge into the larger shank diameter in an area with a 60 ° point angle. Center drills are defined in the DIN 333 standard; Center bores produced with such tools in DIN 332.
Due to the small dimensioned center point, significantly lower radial forces and reaction forces from the chip occur when drilling into the material. These factors reduce a blurring of the drill, whereby the positional accuracy of the hole produced significantly improved. The actual hole can then be drilled with a twist drill, which is guided laterally through the center hole from the start; this is done through the different design of the point angles, which only guide the twist drill at one point on the support surface. However, no deep holes can be made with a center drill (max. Until the full diameter is reached, since there is no flute in the upper area for chip evacuation); it is only suitable for centering.
The transition from the diameter of the centering point to the shaft diameter is designed differently in detail, depending on the selected shape, according to DIN 332 Form R, A, B or C.
The use of NC spotting drills is recommended for machine tools with high geometric rigidity ; This includes machining centers in particular, but also other numerically controlled machines , as they are often very stable. With NC spotting drills, the center point is omitted, which results in shorter drilling paths. Their point angle is 60, 90 or 120 °. Deep holes cannot be drilled with them because they have no guide chamfers.
Conical drill or step drill
Conical drills are used to expand pre-drilled, pre-punched or pre-cast holes. They are mainly used for drilling sheet metal. Their appearance is similar to that of a countersink. In contrast to the twist drill, there are more cutting edges available for drilling. This increases the cutting volume, gives the drill better guidance in thin material and thus increases the roundness of the hole. In order to increase the stability, these drills are usually coated with titanium.
For deep bores, the modular system consisting of a clip-on holder as the drill shank and a shell-type cone drill as the drill head has proven itself. Conical drills are particularly suitable for thin sheet metal, as drilling deeper into metal leads to a short tool life. They are well suited for wood or plastic processing.
- See also: Ausspindler .
External threads are created by cutting dies.
Indexable insert drill
Indexable insert drills are similar in structure to twist drills. They also have grooves for removing the chips. The cooling lubricant is supplied through the tool shank. Indexable insert drill having at least two at the tip or a plurality of exchangeable cutting inserts which are arranged asymmetrically. These consist of a base body made of tool steel with a rake face and flutes to accommodate one or more indexable inserts. Usually two are used, which are fastened with screws in the insert seat. So-called "Eco-Cut drills" represent a special feature: They have an indexable insert with which a centric hole can be made and then turned. Indexable insert drills are used in the diameter range from 16 mm to around 60 mm, in exceptional cases also up to 120 mm.
Strictly speaking, if the indexable inserts are fitted in different radii, these are individually milling cutting edges. The inner plate cuts in the center, while the outer one processes the wall of the hole (with a twist drill, both cutting edges process the same area). As a result, the inserts are loaded unevenly (cutting speed, cutting path), which is why careful adaptation of the material, cutting material and cutting edge geometry is recommended. Because of the lower cutting speed, the inner plate can be made of a softer cutting material than the outer one.
Due to the relatively high feed rates per cutting edge with indexable inserts, the feed rates are comparable to the feed rates that can be achieved with twist drills, despite the lack of a second cutting edge.
Deep drill (metalworking)
Deep hole drilling (or synonymously deep hole drilling) in metalworking begins (according to VDI 3210) with a drilling depth of 3 times the tool diameter.
The difficulty with deep drilling is to minimize the migration of the drill head center away from the set axis, although the drill shank has a lower flexural rigidity due to its length than with normal drilling. This is achieved through two properties of deep drills:
- No blunt cross cutting edge in the middle of the drill tip, which only displaces or scrapes material, requires high drilling pressure and provokes lateral evasive movements of the drill. Instead, the entire cross-sectional area is regularly cut by means of one or more cutting edges.
- Since the drill shank cannot provide a clear definition of the position of the drill head, the wall of the hole that has already been drilled takes over this task. Except for the simplest deep drills, one or more longitudinal webs, so-called guide strips, on the outside ensure this position definition. These are either left standing when the drill head is ground off or specially inserted into grooves. So it is the material of the cuttings that absorbs the lateral forces when drilling. This is why a pilot hole or drill bushing is required at the beginning of the drilling process.
In this way, drilling depths of up to 250 times the tool diameter are possible, with high surface quality and compliance with dimensional tolerances of up to H8 (H7).
The various processes differ mainly in the number of cutting edges - multi-cutting tools are only used with larger diameters - and the supply of the cooling lubricant , which also serves to remove the chips:
- Feed through hole in the tool, discharge between tool and hole wall (single-lip drilling, ELB)
- Infeed between the tool and the wall of the bore, discharge through the bore in the tool (one-pipe system)
- Infeed and discharge inside the tool, through a bore with an internal pipe (double pipe system).
With a smaller diameter, the drill head is made entirely of hard metal, into which the tool geometry is ground, and is soldered onto the drill shank. Larger tool heads are made of steel and have screwed-in hard metal cutting elements.
For some years now, double-edged (extra-long) twist drills have been increasingly used as deep drilling tools. In contrast to single-lip deep drilling tools, the length-to-diameter ratio is limited to around 40. The advantage of this type of tool is a seven-fold increase in machining speed compared to single-lip deep drilling.
For drilling, particularly in concrete, drills with a special shaft ( SDS system ) are used in rotary hammers ; In addition to the rotary movement, these produce regular impact movements in the axial direction. A distinction is made here according to the diameter of the tool holder. SDSplus is usually used for bores up to max. Ø16 mm and light chiseling work are used, while SDSmax is used for larger bores and heavy chiselling work.
With regard to the drill tips, the current state of the art is a solid carbide head with 4 cutting edges (2 main and 2 secondary cutting edges), which can be used optimally especially for reinforced concrete, as the drill does not get caught when it hits a reinforcing iron. The hard metals used are medium to coarse grades with a high proportion of binder in order to achieve the toughness required to absorb the impact.
Welding instead of brazing is now often used as a joining process with the tool steel shaft in the SDS-Plus area. In the large diameter range (SDS-Max), however, this has so far not been possible for technical reasons.
For the drilling of bricks and other building materials with a lower hardness and abrasiveness than concrete, drills with a round shank and soldered carbide cutting edge (plate) are often used. Since the Widia company manufactured this type of drill for the first time, it is also known colloquially as the Widia drill. These are used in so-called impact drills with normal drill chucks.
Drill bit, drill bit
Drill bits, also called drill heads, and drill bits are used for drilling in solid rock (e.g. rotary drilling method ). They destroy the rock in the depth of the borehole. Drill bits destroy the entire bottom of the borehole, and the rock material is flushed out of the borehole as fine cuttings - usually with a liquid mud, in the case of short boreholes also with compressed air.
Another form of drill bit is also used in the craft sector for house installation for setting cavity wall sockets (e.g. for sockets or light switches ). It can be clamped in almost any type of drilling machine .
With this type of drill bit, a guide rod (a round steel or concrete drill) fixed in the center of the bit serves as a centering device so that the drill bit does not "run" during the machining process. Several cutting inserts (mostly hard metal cutting edges ) placed on the side wall of the crown facing forwards mill into the material to be machined. Since the back of the drill bit is closed, the maximum depth of the individual drilling is already predetermined, larger drilling depths require the core to be broken out in the meantime (in order to be able to continue drilling). Many versions of drill bits have a helical groove on the outer cylinder jacket for removing cuttings. There are special versions for use with rotary hammers (hammer drill bits versus rotary drill bits).
Flow drill (flow hole drill)
In contrast to cutting drilling, flow drilling or flow forming (also flow hole drilling or flow hole forming ) is a non-cutting forming process in thin-walled material. The flow drill has a conical tip and an adjoining cylindrical part, which determines the diameter of the resulting hole, but no chip spaces like a conventional drill. The machined material is not machined, but displaced by the force of the drill and the resulting frictional heat and deformed into a bulge-shaped ejection. Flow drills are made of hard metal .
- Drilling wells
- Core hole drilling
- drilling machine
- Drill bit
- Drill bit
- Gun drill
- Crown drills
- Hole saw
- Racing spindle as Dreule known
- Earth auger
- Stage drills , wood screw with out running over the head wand and hand grip for tool-free fixed and loose screws in soft wood of the stage floor
- Rotating dental instruments
- Emil Hoffmann: Lexicon of the Stone Age. P. 57 ff. Verlag CH Beck, Munich 1999, ISBN 3-406-42125-3 .
* Driving, drilling, connecting: Günter Spur: About the change in the industrial world through machine tools. Carl Hanser Verlag, Munich, Vienna 1991, pp. 54–56.
- Drifting: Wolfgang König (Ed.): Propylaea History of Technology - Volume 3. Propylaea, Berlin 1997, p. 101 f.
- Günter Spur: On the change in the industrial world through machine tools. Carl Hanser Verlag, Munich, Vienna 1991, pp. 89, 91 f.
- Wolfgang König (Hrsg.): Propylaen technology history - Volume 3. Propylaen, Berlin 1997, pp. 188-190, 194, 196 f.
- Herbert Schönherr: Machining , Oldenbourg, 2002, p. 164 f.
- TE-CX hammer drill bit - Hilti Germany. (No longer available online.) In: Germany. Archived from the original on November 30, 2016 ; accessed November 30, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- Ceratizit: Hard metals for stone working (No. 258) . Ed .: Ceratizit. 2016.
- drilling method. Spectrum of Science, Lexicon of Geosciences, accessed on October 18, 2015 .