Yeah... cutting acrylic aint easy; and it does crack just
when ya think you're almost home scott-free,
then "snap!" there goes the neighborhood.
It takes a Lot of patience to cut and file acrylic.
Some of the causes for acrylic to break, when cutting it, include
where and how it is cut... ya have to brace it down on a flat
surface so the vibrations from the cutter doesn't cause cracks to form.
The cutter itself has to be a very fine-tooth blade; and pressure
must Not be put against the cutter-- sometimes I've been too
impatient cutting plexiglass just to fix a window, and I break the
plastic from exerting pressure trying to rush through the
cutting process.
When cutting acrylics in a straight line, I've sandwiched the acrylic
between two half-inch thick sheets of plywood bolted together,
and cutting with a fine-toothed blade-- again, letting the blade move
at it's own weight instead of forcing the cut.
This minimizes the vibration from causing the acrylic
to crack against your newly-cut shape...
Other methods I've used have been with a box-cutter and a
aluminum T-Square when cutting straight lines, by repeated
scratching of a straight line along the T-Square while holding
the box-cutter blade at an angle.
Then running the blade in one direction to scratch into the
acrylic until the scratch deepens right through... a gentle flex,
and the new cut piece breaks free.
Then filing the new edges smooth with a fine grinding tip
of a dremel in short sweeps along the acrylic's edge.
Can't do this with curved lines, though.
Here in This case, 45 did the right thing with the small holes
along the shape: that means less acrylic for the blade to cut
as it goes from one hole to the next, again- cutting
Patiently.
This "hole-chain" technique also prevents the build-up of hot
molten acrylic shavings to harden back onto your
newly-cut shape.
Cutting with a dremel is fine, in some circumstances...
but in This case, trying to cut fancy shapes with a dremel can
spell Trouble: the heat from the cutter causes the molten
acrylic shavings to pile up and harden back up again along the
path behind where you've already cut... when that happens,
the acrylic is rejoined and could damage the fancy shape if ya
try to break off the hardened residue.
A dremel may be useful to smooth out the edges of the
newly-cut acrylic: In which a Very fine grinding tip may be used,
in short gentle sweeps along the newly cut edge.
Avoid prolonged grinding along the acrylic edge so that
No molten acrylic residue forms and hardens onto the acrylic
as you grind along its edge.
If you can develop a "writing" technique with the dremel,
practicing on scrap pieces of acrylic, you could come up with
amazing ways to Control the dremel to cut and grind your acrylic
shapes in many kinds of angles, shapes, curves, and lines;
any way you want; and make some really
awesome custom plastic parts.
Hope this helps ;D
zozo-Magengar