<s>
A	O
3D	B-Device
printer	I-Device
extruder	I-Device
is	O
a	O
filament	B-Device
feeding	O
mechanism	O
used	O
in	O
many	O
fused	O
filament	B-Device
fabrication	O
(	O
FFF	O
)	O
3D	O
printers	O
.	O
</s>
<s>
There	O
are	O
several	O
types	O
of	O
3D	B-Device
printer	I-Device
extruders	I-Device
.	O
</s>
<s>
A	O
Bowden	B-Device
extruder	I-Device
is	O
a	O
type	O
of	O
extruder	O
that	O
pushes	O
filament	B-Device
through	O
a	O
long	O
and	O
flexible	O
PTFE	O
(	O
Teflon	O
)	O
tube	O
to	O
the	O
hot	O
end	O
.	O
</s>
<s>
An	O
alternative	O
type	O
of	O
extruder	O
which	O
is	O
also	O
widely	O
used	O
in	O
filament	B-Device
3D	O
printers	O
is	O
the	O
direct-drive	O
extruder	O
,	O
which	O
sits	O
closer	O
to	O
the	O
extruder	O
hot	O
end	O
.	O
</s>
<s>
They	O
also	O
have	O
less	O
chance	O
of	O
tangling	O
the	O
filament	B-Device
while	O
it	O
unwinds	O
from	O
the	O
spool	O
.	O
</s>
<s>
Additionally	O
,	O
they	O
reduce	O
the	O
mass	O
of	O
the	O
extrusion	O
carriage	O
because	O
it	O
does	O
n't	O
have	O
to	O
hold	O
a	O
stepper	B-Algorithm
motor	I-Algorithm
.	O
</s>
<s>
One	O
disadvantage	O
is	O
that	O
because	O
Bowden	B-Device
extruders	I-Device
push	O
filament	B-Device
through	O
a	O
long	O
and	O
curved	O
tube	O
,	O
more	O
friction	O
must	O
be	O
overcome	O
compared	O
with	O
direct	B-Device
drive	I-Device
extruders	I-Device
.	O
</s>
<s>
Flexible	O
filaments	O
do	O
not	O
print	O
well	O
because	O
the	O
filament	B-Device
flexes	O
inside	O
the	O
tube	O
and	O
clogs	O
up	O
the	O
machine	O
.	O
</s>
<s>
Another	O
disadvantage	O
is	O
that	O
the	O
feeding	O
distance	O
is	O
relatively	O
long	O
,	O
and	O
thus	O
the	O
resistance	O
is	O
high	O
,	O
meaning	O
the	O
stepping	B-Algorithm
motor	I-Algorithm
of	O
extrusion	O
is	O
required	O
to	O
have	O
a	O
higher	O
torque	O
.	O
</s>
<s>
With	O
a	O
direct-drive	O
extruder	O
,	O
the	O
motor	O
pushing	O
the	O
filament	B-Device
is	O
installed	O
by	O
the	O
hotend	O
and	O
pushes	O
the	O
filament	B-Device
directly	O
into	O
the	O
nozzle	O
.	O
</s>
<s>
One	O
typical	O
disadvantage	O
of	O
direct-drive	O
extruders	O
is	O
the	O
added	O
mass	O
to	O
the	O
hotend	O
,	O
compared	O
to	O
a	O
typical	O
Bowden	B-Device
extruder	I-Device
,	O
which	O
may	O
cause	O
more	O
vibrations	O
so	O
that	O
the	O
direct-drive	O
printhead	O
has	O
to	O
move	O
slower	O
,	O
which	O
can	O
affect	O
print	O
speed	O
.	O
</s>
