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Basic Drilling
Parts, properties and functions
Margin width
Margin
Flute
Chisel edge
Flute width ratio
Flute width
Cutting edge
(Cutting edge honing)
Margin with
Margin
Land
The margin is a round face that does not have body clearance in the land. The margin section of a drill assists in attaining hole tolerance holes.
The margin width is the width of margin on a cross-section surface orthogonal to an axial centreline of the tool.
The flute of a drill is the section or area behind the cutting edge. It twists up through the body of the drill and is used to evacuate the chips developed while machining.
There are two helical flutes in a drill. Generally the flute geometry is designed so that the cutting edge is straight at a predetermined point angle.
Flute
Cutting edge
Heel
Flute
Chisel edge
The chisel edge of a drill is the cutting edge at the centre point of a drill.
The shorter the chisel edge is the higher the performance of the initial machining, and as a result the higher the accuracy of the drilled hole.
Flute width
Land width
Flute width
Land width
Flute
width
ratio
The flute width ratio is the ratio of the flute width and the land width at the tip of a drill.
As the flute width ratio decreases, both the helix rigidity and flexural strength increase. Additionally the cross-section area of the flute becomes smaller thus leading to poor chip evacuation.
For solid carbide drills, honing of the cutting edges carried according to applications. The larger the honing width or honing angle is the stronger cutting edge. However in doing so the cutting resistance tends to increase.
A-A Cross section
Honing
with
x
There are a large number of angles and terms used to described a drill and it´s properties.
Click on the links to learn more!
Depth of body clearance
Body clearance
Land width
Straight shank width tang
Tang
Neck
Neck length
Outer corner
Height of point
Flank
Shank length
Coolant
hole
Body
Clearance angle
Web
Lead
Point angle
Overall length
Shank
Back taper
Flute
Coolant hole
Recently, drills with coolant holes have become the mainstream. This is due to the many advantages associated with through coolant holes. Advantages such as, coolant is supplied directly to cutting edge, efficient chip discharge and the elimination of adjusting the coolant supply nozzles in the case of external coolant supply.
In comparison to drills without coolant holes, drills with coolant holes can be used with higher cutting speeds and feed rates. Therefore enabling high machining efficiency to be achieved.
The body of the drill is from the front end of the shank to the outer edge of the cutting edge.
Body
A-A Cross section
At the outer cutting edge corner, the angle between a cross-section surface orthogonal to the axial centreline of the drill and the flank face, represents the clearance angle. As the clearance angle becomes larger the cutting edge strength reduces..
Clearance angle
Cutting
edge
The web is a section of the drill that represents the core of the drill. The purpose of the web is to provide the drill with rigidity.
There are two kinds of web geometry, a parallel web and a taper web. The thicker the web is then the higher the helix rigidity and flexural strength become.
The web thickness represents the thickness of the web at the point if the drill.
Web thinning is a particularly process in which a portion of the chisel edge is made smaller. By applying web thinning it reduces cutting resistance experienced at the chisel edge. It also assists in improving chip disposal and as such offers longer tool life and higher hole accuracy.
Web
thick-
ness
Parallell
Taper
Web
Web thinning
Cutter sweep
Leading edge
Lead
The lead of a drill is the distance the leading edge advances axially in one revolution.
118°
130°~140°
The point angle is the angle measured by casting a reflection of the cutting edge on a plane parallel to a drill axis.
Usually, high-speed steel drills use a point angle of 118°, whereas the point angle for solid drills is between 130°~140°.
Outer corner
Overall length
overall length of a drill is the length from the outer cutting edge to the end of the shank. It is measured parallel to the axial centreline of the drill.
Shank
The shank is the portion of the drill that will be clamped or held in a collet or holder.
Back taper, is a slight decrease in the drill diameter towards the shank of the drill. This is designed to prevent the drill periphery from rubbing the inner wall of a hole while drilling. The larger the back taper the lower the cutting resistance. However due to the decrease in the tool diameter, the number of times regrinding can be carried out is limited.
Back taper
Flute
Flute
Cutting edge
Heel
The flute of a drill is the section or area behind the cutting edge. It twists up through the body of the drill and is used to evacuate the chips developed while machining.
There are two helical flutes in a drill. Generally the flute geometry is designed so that the cutting edge is straight at a predetermined point angle.
x