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Incorporated, a worldwide network of science museums and related institutions.
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We drill holes through Plexi all the time with regular drills. The trick
is quite simple: Grind the flutes at the point to eliminate the "lips"
on the drill's end. A regular bit has the cutting angle quite shallow if
you look at it from the side. (Sort of like a gradually increasing
incline plane that spirals, usually there are two of these in most
smaller bits.) Carefully grind the flutes so there is a short distance
with the cutting angle being a sharp 90 Degrees. Figure in a 1/2"
diameter bit that this 90 degree part should be about 0.050" in height.
This will prevent the drill from grabbing. The remainder of the spiral
flutes will still allow for chip removal. By the way, this trick also
helps in drilling soft metals like brass and aluminum (in soft grades)
and copper. 

The second trick with plastic is to keep the rotational speed of the
drill low to reduce the surface cutting speed. Plastic has virtually no
ability to remove heat from the hole being drilled. The friction rapidly
heats up the drill and soon you are melting your way through. It can
also help to have a small cup of water handy to periodically cool the
drill down, especially in the case of deep holes.

By the way, this matter of keeping the bit cool applies to hand taps as
well! It is quite amazing how hot a tap can get tapping even a small and
short hole. Watch the heat as your threads will be lousy if you don't.

Hope this helps!

John Bowditch

-----Original Message-----
From: Informal Science Education Network
[mailto:[log in to unmask]] On Behalf Of Albert J. Read
Sent: Monday, June 26, 2006 5:33 PM
To: [log in to unmask]
Subject: Re: film canister alternative

ISEN-ASTC-L is a service of the Association of Science-Technology
Centers
Incorporated, a worldwide network of science museums and related
institutions.
************************************************************************
*****

A pair of suggestions for Jonah Cohen and others regarding the challenge
of drilling holes through brittle plastic.....

1. Experiment with using a hot soldering iron to melt holes through the
plastic rather than drilling.  Note that there are several diameters of
tips available.  It would be prudent to do this in a well-ventilated
area since some fumes are produced. This technique even works well with
plastic cups and bottles.

2. Experiment with first drilling a rather small hole (like 1/8 or 3/16
inch) and then enlarging it to the size you want with a taper reamer.  

Albert J. Read, Director Emeritus, Science Discovery Center of Oneonta
(NY)




-----Original Message-----
From: Informal Science Education Network on behalf of Jonah Cohen
Sent: Mon 6/26/2006 4:54 PM
To: [log in to unmask]
Subject: Re: film canister alternative
 
ISEN-ASTC-L is a service of the Association of Science-Technology
Centers
Incorporated, a worldwide network of science museums and related
institutions.
************************************************************************
*****

In a similar vein, you could pony up some cash for snap-seal vials
(available from Flinn Scientific... and doubtlessly other places, too).

Pity yours truly! While such vials are certainly a useful film can
stand-in
for many experiments (like the alka seltzer rockets), they're less
useful
for the PVC sound pipes. You have to drill a hole in the bottom of the
canister. Easy for film cans, less so with the rigid plastic of pill
bottles
and snap-top vials.

Did I mention that we do a class where kids make their own individual
version of this instrument and get to keep it, ergo a constant need for
more
canisters? Sheesh, what moron came up with this idea?

Oh, right, it was me,
Jonah Cohen
Outreach & Public Programs Manager
The Children's Museum (formerly the Science Center of Connecticut)

"The difference between genius and stupidity is that genius has limits."
         -Albert Einstein

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