| Cause |
Failure condition |
Countermeasure |
D
r
i
l
l
B
i
t
D
e
s
i
g
n |
Small chip
pocket (flute volume) |
Poor chip evacuation causes bird nesting. |
Enlarge chip pocket volume, change web thickness
web taper, and flute land ratio. |
| Short flute length |
Poor chip evacuation causes bird nesting at the
flute end. |
Apply suitable flute length for stack height. |
| Large helix angle |
The axial direction does not promote good chip
evacuation, causing Bird Nesting at the end of the flute |
Lower helix angle. |
| Small point angle |
Because the Chip isn't cut (divided), it becomes
a continuous form. |
Enlarge point angle. |
D
r
i
l
l
i
n
g
C
o
n
d
i
t
i
o
n |
Low chipload / Low spindle speed |
Low chipload generates a long, thin chip form,
causing Bird Nesting at the end of the flute. Low spindle speed
removes the centrifugal force effect to drive the swarf away |
Higher chipload / Higher spindle speed |
| Penetrating to deep into the backup board |
Materials such as Backing Board generate large
particles of swarf which can adhere to the drill causing Bird
Nesting. |
Set suitable penetration depth. |
| No dwell time between drilling strokes |
Bird Nesting occurs because the drill has not
completed the evacuation process |
Use dwell time. |
P
W
B
S
e
t
t
i
n
g
|
Thick lubricant resin on entry board |
Bird nesting occurs at end of flute, and can cause
breakage in extreme cases. |
Change to thinner lubricant layer type. (Note
that this can cause hole registration accuracy to worsen) |
| Unsuitable entry board |
On thicker PWB's, bird nesting occurs more easily
because of the uncut chip from the entry board. |
Consider suitable thickness. |
| Hinge number and thickness of PWB copper layers |
Bird nesting occurs because of spiral copper chip. |
Higher chipload |
E
q
u
i
p
m
e
n
t |
Unsuitable bush diameter (restricted air flow) |
Chip evacuation is less effective due to the smaller
inner bush. |
Change large diameter bush. |
| Unsuitable vacuum force |
Poor chip evacuation is increased with a low vacuum
force, especially with larger ID drills |
Set a suitable vacuum force. Clean pressure foot
and hoses. Maintain dust catcher. |
