40 SERVO 09.2013
The down side to using Kapton tape is that is can
sometimes be difficult to remove the finished print, and
damage to the Kapton tape can occur. If you do damage
the tape, you will need to replace it.
Note that some objects can be printed on blue painter's
tape. It does not have the adhesion that Kapton does, but it
can work in a pinch.
PLA to the Rescue
Okay. Now you understand some of the downsides of
printing with ABS. What are our alternatives? The answer is
PLA which is a bio-degradable plastic made from corn or
other plants. It warps very little and does not smell as bad
as ABS. Corn is used in US-made PLA, but since other
plants may be used on imported PLA, the properties may
PLA Melting Point
PLA has a lower melting point than ABS and so it prints
at a lower temperature than ABS. This lower melting point
is one of the major disadvantages of printing with PLA. As
PLA is printed, the heat from the extruder nozzle can creep
up the extruder and soften the filament as the print
progresses. This softening can cause the filament to jam
inside the extruder.
To solve the jamming problem, a fan like the one
shown in Figure 11 can be used to keep the filament from
getting soft inside the extruder. Figure 12 shows a set of
cooling fans used to cool the filament in a dual extruder.
Unlike ABS, PLA cannot be left with the extruder heated
for any length of time without extruding filament. When
heated for short periods of time without extruding, PLA will
caramelize. This action will clog the extruder nozzle.
PLA Bed Adhesion
I have found PLA to stick reliably to three surfaces: glass
heated to 65-75 degrees Celsius; Kapton heated to 65-75
degrees Celsius; and unheated acrylic. That's not to say it
won't stick to other surfaces; it's just that these are
my top three.
PLA sticks best to unheated acrylic. I like to use a
fine sanding sponge to scuff the surfaces as shown in
Figure 13. Try not to use solvents like alcohol on
acrylic or it may start to chip and crack like the sheet
shown in Figure 14.