A reader's question about drilling acrylic is answered by one of PBO's experts

QUESTION: 

Are there any special things I should know about drilling acrylic? I want to drill some holes quite close to the edge of a piece around 8mm thick. Any tips would be greatly appreciated.

Bill Carr
By Email

DICK EVERITT REPLIES:

Special acrylic drilling bits are
ideal, but I’ve managed with
ordinary twist drills. Practise on a
scrap piece of acrylic and if there
is a tendency for the drill to dig in
and chip the surface, grind the
drill’s cutting edges back a bit.
Simply fl atten them against the
side of the grinding wheel, as
shown in the photo.
A drill press is great for keeping
everything square, but a manual or
powered hand drill also works fi ne.
Clamp the acrylic down carefully,
being careful not to scratch the
surface, and have a scrap piece of
acrylic or hardwood underneath.
This gives the right resistance to
the drill point as it keeps cutting
and prevents the sides of the drill
from bursting through and
chipping the edge of the hole.
Use a slow speed, drill a pilot
hole and make a circular dam of
plasticine around the hole to hold
water to lubricate and cool the job.
Work slowly and keep taking the
load off the drill so it doesn’t heat
up and crack the plastic.
If the hole is for a bolt, drill it
slightly oversize and rub off the
sharp edges with a countersink or
larger drill, to prevent stresses
building up as you clamp
everything down.
There are all sorts of acrylic
plastics: some drill like soft cheese,
others seem to work-harden and
always want to chip, so good luck!
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