Drilling

Question 1

Drilling: definition

Answer 1

Machining operation that creates a round hole in the workpiece

Question 2

types of holes

Answer 2

• through holes: open on both sides
• blind holes: open on one side
• countersink: conical entrance to help inserting a piece
• Counterbore: useful for fixing

Question 3

twist drill: characteristics

Answer 3

• 2 helics
• helicoidal flutes allow the chip removal
• possible cutting fluid inside the drill
• diameter of the body smaller than the extremity to reduce friction
• web: no cutting speed near the center, so a web is used instead of a cutter to increase the robustness of the tool

Question 4

reaming operation

Answer 4

finishing operation to improve the quality of the hole

it consists in enlarging an existing hole, obtaining a better surface finish

Question 5

basic rules to obtain a good holeq

Answer 5

1. generate a flat entrance for the drill, to avoid bending

2. possibly, drill the hole in many passes, increasing the diameter of the drill

Question 6

tapping operation

Answer 6

a particular shape of the drill defined the internal shape of the hole

to maintain the internal surface, at the end of the hole the drill stops and restarts in the opposite direction to exit

Question 7

work holding for drill presses

Answer 7

1. vise: workholder with two jaws
2. fixture: custom device designed for the particular workpiece
3. drill jig: provides a guide for the tool during drilling

Question 8

types of machines for drilling

Answer 8

1. drill press
   - base
   - table
   - vertical spindle
   - column
2. radial drill press
   - for large parts
   - column
   - axial movement
   - vertical spindle
   - table
3. CNC drilling machine
   - table
   - turret
   - column

Question 9

cutting forces in drilling

Answer 9

• forces due to chip formation, perpendicular to the cutting edge
• forces due to friction on flank faces
• force on the web due to the feed