cutting methods & forces

Question 1

orthogonal cutting

Answer 1

• tool cutting edge set at 90°
• tool curls chip in form of clock spring/flat spiral = chips stay on top of tool holder & damage workpiece’s surface

1) Tangential Force:
tangential to the work surface; MAIN POWER-CONSUMING FORCE

2) Axial Force:
\ to work axis & resists feed motion; relatively small force

Question 2

oblique cutting

Answer 2

• tool cutting edge set at any angle other than 90° = twisted curl chip formation
• inclined cutting condition improves surface finish = chips move away freely from cutting area

1) Tangential Force
2) Axial Force

3) Radial Force:
insignificant; tend to force tool out of work & is resisted by friction in cross slide & leads screw; no motion associated as it does not consume power but influences A.F

Question 3

characteristics of cutting tool materials

Answer 3

• hot hardness;
  ability to retain hardness at elevated temp
• toughness;
  ability to resist shocks & impacts
• abrasion resistant;
  due to low coefficient of friction, good surface finish & good tool material
• economical;
  reasonably cheap & easily fabricated/shaped
• others: tensile strength, thermal conductivity, coefficient of thermal expansion, module of elasticity

Question 4

+ve rake angle tools

Answer 4

rake angle increase; 
tool bcomes weaker;
reduced cutting force & power;
increase side rake angle;
improves machined surface finish;
provides sharper edge;
increase tool life

Question 5

-ve rake angle tools

Answer 5

rake angle decrease;
strengthened cutting area;
cutting forces supported by tool body;
tools used for higher cutting speeds;
poor surface finish;
rapid cutting + chip friction = heat;
no time to pass to tool, almost all heat is concentrated in chip;
chip bcomes more plastic;
forms thin continuous chip