Jobber Drills
The term Jobber drill comes from this tool's popularity, they are the most commonly found and often get used in lots of jobs
Drilling is the process of cutting or originating a round hole from the solid material. The tool (drill) and not the work piece is revolved and is fed into the material along its axis. For example, according to material, number and types of flutes, drill size, type of shank(straight or taper) and cutting point geometry etc. However the most common type of drill is the fluted drill as in the diagram below:
The point comprises the cutting elements while the body guides the drill in the operation. The body of the drill has two helical grooves called “ flutes”. The flutes from the cutting surface and also assist in removing chips out of the drilled hole. The parts of twist drill are:
1: Point:
The point is the cone shaped end and it does the cutting. It consists of the following:
(A) dead center: It is the sharp edge at the extreme tip of the drill. This should always be the exact center of the drill.
(B) Lips: these are the cutting edges of the drill.
(C) Heel : It is the portion of the point back from the cutting edge.
2: Shank :
It is the portion of the drill by which it is clamped in the spindle. The shank may be either straight or tapered. Straight shank drills are used with a chuck. Tapered shank drills have self-holding tapes that fit directly into the drill press spindle. On the taper shank is the another term is used which is called tang. This fits into a slot in the spindles sleeve.
3: Body :
It is the portion between the point and the shank. The body consists of the following parts:
(A) Flutes - Two or more spiral grooves that run the length of the drill body are called flutes. The flutes do four things: help from the cutting edge of the drill point, curl the chip tightly for easier removal, Form channels through which chips can escape from the hole being drilled. Allow the coolant and lubricant to get down to the cutting edge.
(B) Margin - It is the narrow strip extending back the entire length of the flute. It is the full diameter of the drill.
(C) Body Clearance: - It is the part of the drill body that has been reduced in order to cut down friction between the drill and the wall of the hole.