drilling tool design

8/19/2019 Drilling Tool Design

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Design of Drill Bit

Drill can be defined as a rotary end

cutting tool having one or more cutting lips, and

having one or more helical or straight flutes for the

passage of chips and the admission of a cutting fluid.


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Classification

A. Classification Based on Construction

1. Solid Drills: Those made of one piece of material

such as high speed steel

2. Tipped Solid Drills: Those having a body of one

material with cutting lips made of another material braed

or otherwise bonded in place

!. Composite Drills: Those having cutting portions

mechanically held in place

B. Classification "ased on Methods of Holding orDriving

1. Straight Shank Drills: Those having cylindricalshan#s which may be the same or different diameter

than the body of the drill$ the shan#s may be madewith or without driving flats, tang, grooves or threads

2. Taper Shank Drills: Those having conical shan#ssuitable for direct fitting into tapered holes in machinespindles, driving sleeves or soc#ets$ tapered shan#sgenerally have a driving tang

!. Taper Shank Square Drills: Those having taperedshan#s with four flat sides for fitting a rachet or brace

%. Shell Core Drills: Core drills mountable on arborsspecifically designed for the purpose$ commonly used


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with shell reamer arbors&. Threaded Shank Drills Those made with threadedshan#s generally used in close center multiple spindle

applications or portable angle drilling tools

'. Beaded Shank Bits: Drills with flat shan#s havingraised beads parallel to the a(is

C. Classification Based on Number of Flutes

1. Two-lute Drills: The conventional type of twist drillused for originating holes 2. Single-lute Drills: Those having only one fluteonly used for originating holes !. Three-lute Drills !Core Drills": Drills commonlyused for enlarging and finishing, drilled, cast, or punchedholes$ they will not produce original holes %. our-lute Drills !Core Drills": )sedinterchangeably with three*flute drills$ they are of similarconstruction e(cept for the number of flutes

#o$enclature of Twist Drills and %ther Ter$s &elating

to Drilling

A'is: The imaginary straight line which forms thelongitudinal center line of the drill Back Taper : + slight decrease in diameter from frontto bac# in the body of the drill Bod(: The portion of the drill e(tending from theshan# or nec# to the outer corners of the cutting lips


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Bod( Dia$eter Clearance: That portion of the landthat has been cut away so it will not rub against the wallsof the hole

Built-)p *dge: +n adhering deposit of nascentmaterial on the cutting lip or the point of the drill Ca$ &elief : The relief from the cutting edge to thebac# of the land, produced by a cam actuated cutting toolor grinding wheel on a relieving machine Chip Breaker : ic#s or -rooves designed to reducethe sie of chips$ they may be steps or grooves in thecutting lip or in the leading face of the land at or adacent

to the cutting lips Chip +acking: The failure of chips to pass throughthe flute during cutting action Chipping: The brea#down of a cutting lip or marginby loss of fragments bro#en away during the cutting action Chisel *dge: The edge at the end of the web thatconnects the cutting lips

Chisel *dge Angle: The angle included between thechisel edge and the cutting lip, as viewed from the end ofthe drill Clearance: The space provided to eliminateundesirable contact between the drill and the wor# piece Clearance Dia$eter : The diameter over the cutaway portion of the drill lands

Drill Dia$eter : The diameter over the margins of thedrill measured at the point

*'posed ,ength: The distance the large of a shan#proects from the drive soc#et or large end of the taper ringgage *'ternal Center : The conical point on the shan# end


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of the drill, and the point end on some sies of core drills lat Drill: + drill whose flutes are produced by twoparallel or tapered flats

lat !Spade" Drill: + removable cutting drill tipusually attached to a special holder designed for thispurpose$ generally used for drilling or enlarging coredholes lutes: /elical or straight grooves cut or formed inthe body of the drill to provide cutting lips, to permitremoval of chips, and to allow cutting fluid to reach thecutting lips

lute ,ength: The length from the outer corners ofthe cutting lips to the e(treme bac# end of the flutes$ itincludes the sweep of the tool used to generate the flutesand, therefore, does not indicate the usable length of theflutes

Helical lutes: 0lutes which are formed in a helical

path around the a(is Heli' Angle: The angle made by the leading edgeof the land with a plane containing the a(is of the drill ,and: The peripheral portion of the body betweenadacent flutes ,and idth: The distance between the leadingedge and the heel of the land measured at a right angle tothe leading edge ,ead: The a(ial advance of a leading edge of theland in one turn around the circumference ,ips: The cutting edges of a two flute drill e(tendingfrom the chisel edge to the periphery ,ip &elief : The a(ial relief on the drill point


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,ip &elief Angle: The a(ial relief angle at the outercorner of the lip$ it is measured by proection into a planetangent to the periphery at the outer corner of the lip

Materials of drill

any different materials are used for or on drill bits,depending on the reuired application. any hard

materials, such as carbides, are much more brittle thansteel, and are far more subect to brea#ing, particularly ifthe drill is not held at a very constant angle to the wor#piece$ e.g., when hand*held

1 Steels2 Tungsten carbide

! polycrystalline diamond 3pcd4

Cutting forces in drilling


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5n a drill there are two main cutting edges and a smallchisel edge at thecentre as shown in above 0ig.The force components that develop 3during drilling

operation are :6 + pair of tangential forces, 7T1 and 7T2 3euivalent to 78 in turning4at the main cutting edges6 +(ial forces 791 and 792 acting in the same direction6 + pair of identical radial force components, 71 and 726 one additional a(ial force, 79e at the chisel edge which

alsoremoves material at the centre and under more stringentcondition.7T1 and 7T2 produce the torue, T and causes powerconsumption 7C as,


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T ; 7T ( < 3D4and 7C; 2=Twhere, D ; diameter of the drill

and ; speed of the drill in rpm.The total a(ial force 79T which is normally very large indrilling, is provided by79T ; 791 > 792 > 79e "ut there is no radial or transverse force as 71 and 72,being in opposite direction, nullify each other if the toolgeometry is perfectly symmetrical.

drilling tool design

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