FINE BORING GUIDELINES Major Influences of Fine Boring • The amount of stock to be removed (D.O.C.) • Feed rate • Cutting speed
For all of these influences, a balance must be obtained for optimal machining. Too much stock or too heavy of a feed rate will generate excessive cutting forces that can result in inconsistent bore size. When stock or feed rates are too light, the possibility of chatter increases due to deflection.
D.O.C
High Possibility for Deflection & Chatter: When D.O.C. is less than half the insert nose radius, the resulting forces (F) are almost 100% radial. Good Stable Cut: When D.O.C. is greater than or equal to half the insert nose radius, the resulting forces (F) are almost 100% axial. High Possibility for Deflection & Chatter: When the feed rate is less than the hone on the insert tip, the risk of vibration increases. Good Stable Cut: When the feed rate is larger than the hone on the insert tip, full use of the chip breaker is allowed. This results in lower cutting forces.
F
< 1/2 Nose Radius
F
≥ 1/2 Nose Radius
FEED RATE
IPR
IPR
CUTTING SPEED Higher Speeds: • Better surface finish • Shorter machining times • Better chip evacuation
As a general rule, the tool’s length/diameter ratio and insert radius will determine optimum cutting speed. For smaller diameter bores, carbide or heavy metal bars may be required to eliminate vibration & chatter
Lower Speeds: • Poorer surface finish • Low chance for chatter • Longer machining times • High chance for built-up edge, results in shorter insert life
L/D Ratio
Max Insert Radius
Speed Reduction
≤ 4:1 ≤ 5:1 ≤ 6:1 ≥ 7:1
.031 .016 .008 .008
100% of optimum 75% of optimum 60% of optimum 50% of optimum
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