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HINTS, TIPS, IDEAS ON DRILLING

 

Chips clogging flutes is the major cause of twist-drill failure.
When hole depth is grater than three diameters, consider it a deep hole.
"Peck" drilling is required to remove chips when drilling deep holes.
Feed rate is the major controlling factor in breaking up chips.
A split-point or a thinned web will reduce thrust on the drill.
Tool design (chipbreaker) can help control the breaking of chips.
Coolant helps wash away chips and prevents tool and work from overheating.

CHATTER-LOCATE THE CAUSE, AND CORRECT IT:

Work must be adequately supported and held.
The tool must be amply rigid to withstand heavy feeds without twisting; use the shortest tool possible.
Spindle must have capacity to supply steady power to a multidrill unit.
The entire machine must resist deflection under working load.
The fixture should be rigid enough to withstand the work forces.

DEEP HOLE DRILLING:

Practically all holes 0.050" or smaller are in the deep-hole category.
Webs of small drills are proportionately thicker than larger drills.
Lip relief angle should be greater on small drills.
Avoid the tendency to overspeed and underfeed drills, they must produce chips, not powder.
Peck drill just enough to prevent packing chips in the flutes.
Decrease speeds and feeds as holes get deeper:

Depth/dia. ratio Speed reduction Feed reduction
3 10% 10%
4 20%  
5 30% 20%
6-8 35-40%  

COOLANTS

Prime purpose is to prevent heat buildup. Flooding also helps wash away chips.
Water is the best coolant known (water-based fluids are preferred).
Coolants must contain rust inhibitor. Avoid coolants that become rancid.
A coolant with good lubricity can help improve hole quality.

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Copyright 2000 ZABEL PUBLICATIONS
Last modified: October 02, 2001