Hi, Gang: I have a piece of Plexi 1/4" thick that needs four holes drilled
in it. Size yet to be determined, but under 1/4". I did this in school thirty
years ago but not since and need a memory upgrade. Any tips appreciated.
Roger in Vegas
Worlds Greatest Impulse Buyer
You can use regular twist drills but you gotta keep 'em COOL or the
Plexi will melt and leave a raised ridge around the holes, or worse,
melt so much that the hole becomes oversized.
Keep the drill speed low and don't try and "punch" the drill through
with too much pressure.
If the Plexi is horizontal you can build a low dam of modeling clay
around the spot you're drilling and put a little water in it to help
keep the drill cool.
If you've got some extra Plexi, you might want to PRACTICE a little
until you know you can drill the workpiece properly.
HTH,
Jeff
Make sure that both sides are masked: if the original covering paper has
been removed use masking tape to insure that both sides are masked where
the holes are to go.
Masking will reduce chipping as the bit enters and leaves the material.
drilled
thirty
IIRC, that material undergoes a tremendous expansion rate on temperature
change, so suggest drill oversize if the piece is very large at
all--otherwise, it will crack--or else your fastener heads will break off
upon weather changes.....
What exactly is the application ???
The material is very prone to cracking. I have good luck using a
step drill (Unibit).
(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)
snipped-for-privacy@7cox.net
I always reduce the grind angle on bits I use for drilling plastics. I
picked up a set of mid quality drill bits at Harbor freight, and used
them for various items, and when they needed resharpening, I just
gro9und them to a lesser rake angle and put them asside for plastics.
Less rake and reduced pooint angle keeps them from grabbing and
chipping the exit side of the holes, and really makes a nice clean
hole.....I use center cutting endmills as well in some cases, for
larger holes.
=============================================Put some color in your cheeks...garden naked!
~~~~ }<((((o> ~~~~~~ }<{{{{o> ~~~~~~~ }<(((((o>
With hole diameter less than thickness, there shouldn't be a lot of
problems. You will probably have some chipping as a regular drill
exits. If the hole is very near the edge, you may crack the material
hole-to-edge.
If you can buy a drill bit specifically made for plexiglass, most of
these problems will disappear. Any plastics supplier will have the
drill bits.
Tim.
Along with all the other tips don't use any kind of oil on it. If you
do it will crack. Maybe not right away, but it will for sure crack. No
doubt about it. Water is really best for a coolant.
ERS
Really? I always used cooling fluid (water + oil). But I never realized
that this might be the cause for cracks. Yes, I had some/many fine but
_only_ after glueing. I always thought that it has something to do with
the way I glue (UV-hardening glue).
astonished,
Nick
--
WDR Fernsehen:
"Ein Computer arbeitet so lange Befehle ab,
I don't think the oil CAUSES the cracks, but, as I understand it, the
machining produces microcracks. The oil gets into these and causes them
to spread (propagate). Eventually the whole area around the hole or cut
just about crystallizes and crumbles from all the little cracks. Tapped
holes are especially prone to this. Anyway, it DOES happen.
Water does indeed seem to be the safest coolant/lubricant. ANY residual
oil is asking for trouble. I have tried wax, and this does not seem to
have the same degree of problem as oil. Perhaps some, but I've not
decided one way or the other yet. Some micro-cracking is normal.
Like many things, the plastic can have internal strains that are
released during the cutting process. This may aggravate the cracks.
Sometimes the plastic can be annealed to relieve this effect. It is
heated evenly to a temperature below it's melting point, and allowed to
set for a while, then slowly cooled. This may reduce cracking. I've not
done this, and usually get decent results without needing it.
What I do that DOES help a lot ... AFTER the cut is finished, seal any
cracks(most are invisible at this point). This can be done with either
heat (fire polishing)if it's an open surface, or a solvent chemical like
Methylene chloride (liquid acrylic cement ... nasty stuff, use suitable
gloves and good ventilation) which can be used even inside a hole. Even
lacquer thinner may work fairly well (depends on the brand, as all are
NOT alike). The solvent needs to melt the surface slightly, thus fusing
any tiny cracks into the main body of the plex. A drop into a small hole
should work fairly well. Let the plex dry and harden before trying to
use the part. Some minor rework may be needed after for critical surfaces.
Dan Mitchell
===========
ACK
Sounds reasonable. So I accept your oily oppinion. :-)
Oh yes, they do! I think Plexiglas XT (extruded) is worse than the GS
(or G? anyhow, the casted one)
I did this and it helps. But you can make it wrong too. 60 deg. C for
several hours is OK, 70 deg. C will make new wraps. :-(
Polishing helps most. 240 grit, then 400 grit whet, then a special
Plexi-polish. For glueing, polishing is not required, the 400 whet is
good enough.
I had bad experiences with acetone. It introduced cracks (_very_ fine,
but a lot). I think that the plexi swells a tad with the solvent,
deforms and when the solvent vapors you get the cracks. Not a proven
theory, just my experience. So I stay away from _any_ solvents (except
for glueing, but there the solvent vapors much slower).
Thanks for the insight,
Nick
--
WDR Fernsehen:
"Ein Computer arbeitet so lange Befehle ab,
I always regrind bits to almost no rake (bit scrapes instead of cuts) and use a mix of
water and dish soap on it when drilling. Holes are clean, no breakout on bottom (use back
board on bottom of course). If you go to a place that sells "drill bits for plastic" just
look at the way they are ground. Otherwise they are just regular twist bits. regards,
Joe.
On Tue, 24 May 2005 11:59:05 -0400, "Daniel A. Mitchell"
Take a look at a plexiglass pepper mill. They will be molded, with
maybe a little machining done to hold the grinder parts. And then
again, maybe not. However, it doesn't matter. They ALL develop cracks
eventually. The oil from the peppercorns gets into tiny cracks,
scratches, whatever, and cracks form.
ERS
On Tue, 24 May 2005 16:32:31 +0200, snipped-for-privacy@gmx.de (Nick Müller)
wrote:
The worst think is that the cracks may not form for months. It depends
to some degree on how much stress is put on them. I built some vacuum
chamber lids out of 2 inch plexiglass that were about 28 inches in
diameter. I had to polish out all scratches. The polish used contained
no oils or alcohols. The lids worked fine but were prototypes. The
production ones went to a different shop that was better equipped to
do parts as large as these. All the lids they made failed when
stressed with the vacuum. Turns out they used coolant with soluble oil
and polished out scratches with abrasive powder mixed with the same
coolant. All the subsequent lids they made were kept well away from
any oils.
ERS
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