[sci.electronics] Machining Plexiglas

jgd@rsiatl.UUCP (John G. De Armond) (01/15/90)

In article <847.25aff5f4@simpact.com> jeh@simpact.com writes:

> (Mark Robert Thorson) writes:

>> You can also cut it with a straight handsaw, like what you would use on
>> plywood.  That produces a cleaner edge.  Most power tools don't work very
>> well on Plexiglas.
>
>In my limited experience, a small table saw will work fine, PROVIDED that you 
>have a carbide-tipped blade in it.  Expensive, but will last a long time.  
>Or, the Plexiglas dealers sell special blades for the purpose.  But scribe 
>cutting as described by Mark is fine for working with eighth-inch stuff.  
>In quarter-inch I've usually found that the scriber makes too curved an 
>edge for gluing -- I don't feel like filing down variations that large.  
>No doubt my technique needs to be improved. 

I've found an even easier way to cut plexiglass than that.  Use pretty much
any fine toothed saw and direct a strong stream of compressed on the kerf.
I use a blowgun with a clamp attached.  The tip is about 1/4" away from the
blade.  This blast of very cold air will stop localized melting which is
the root of most cutting problems.  I use this on both a sabre saw and
a circle saw.  I run the circle saw on a variac to slow it down a bit
for more controlability but I suspect it would work fine at full speed.

I've tried a water mister but it makes a bloody mess and is no more
efficient at cooling.

John


-- 
John De Armond, WD4OQC                     | The Fano Factor - 
Radiation Systems, Inc.     Atlanta, GA    | Where Theory meets Reality.
emory!rsiatl!jgd          **I am the NRA** | 

gnome@mach1.atc.olivetti.com (Gary) (01/16/90)

If you have a problem with twist drills causing
snags and chips around the hole, try using an old
drill and use a file to dull the cutting edge.  This
causes the plexi to be scraped away instead of chipped
off.  I've found this to be true with plexi and polycarbonate
sheet (Lexan).

Gary

brianr@tekig5.PEN.TEK.COM (Brian Rhodefer) (01/16/90)

While I was going to college, I had a summer job with a firm
that specialized in products called "lightplates", which were
.2" thick (or so) Plexiglas panels that provided illuminated
legending for aircraft cockpit controls.  All the cutting tools
that we used, whether carbide-tipped or not, were custom-ground
for use with Plex.  The crucial feature, I was told, is that most
"stock" mills, drills, and blades are sold for use on metals, and
have a shallow "rake angle" - the angle that the cutter's leading
edge makes with the work surface.  Plex tends to burn and "grab"
badly with these kinds of cutters, and works best with rake angles
near 90 degrees.

To see the effect, try smoothing off the cut edge of a scrap of
Plexiglas with a pocketknife.  You'll get the best results when
you use the knife as a scraper, perhaps even with a negative rake angle.


If you do a lot of work with Plexiglas, you might try asking for
Plexiglas cutting tools next time you buy drill bits or sawblades.

Brian Rhodefer

jbm@eos.UUCP (Jeffrey Mulligan) (01/17/90)

gnome@mach1.atc.olivetti.com (Gary) writes:

>If you have a problem with twist drills causing
>snags and chips around the hole, try using an old
>drill and use a file to dull the cutting edge.

Use a stone instead of a file.

The plexi drill I have seen had a small bevel ground on the cutting edge
at approx 45 degrees.  This perhaps had a width of 1/32" on a 1/2 inch
drill.

Plexi can be cut cleanly and easily without a saw by first scoring
along a line, then placing the scored sheet on top of a broom handle
or dowel, and striking a sharp blow.  This works best for smaller cuts.


-- 

	Jeff Mulligan (jbm@aurora.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035
	(415) 694-3745

mikemc@mustang.ncr-fc.FtCollins.NCR.com (Mike McManus) (01/18/90)

In article <5982@eos.UUCP> jbm@eos.UUCP (Jeffrey Mulligan) writes:

>   Plexi can be cut cleanly and easily without a saw by first scoring
>   along a line, then placing the scored sheet on top of a broom handle
>   or dowel, and striking a sharp blow.  This works best for smaller cuts.

You can do this for larger cuts, but make sure that the score is deep enough.
Plexi likes to "run off course" if the score line is not sufficiently deep.
You may want to score both side of the sheet to help prevent this, but unless
you are extremely careful, this tends to make for less-than-flat edges.  Also,
what sometimes helps is to score the edges of the sheet with the file on the
ends of the score line, this helps to "start" the break when you strike it.

Also, I've found that what works well to hold plastic is hot glue (ala hot glue
"gun").  It holds really well, but if for some reason you need to seperate
parts, you can usually cool down the area (freezer or ice cubes work well) and
pry them apart.  Doesn't look real nice, tho, so you may want to keep the hot
glue joints out of sight.
--
Disclaimer: All spelling and/or grammer in this document are guaranteed to be
            correct; any exseptions is the is wurk uv intter-net deemuns.

Mike McManus (mikemc@ncr-fc.FtCollins.ncr.com)  
NCR Microelectronics                
2001 Danfield Ct.                   ncr-fc!mikemc@ncr-sd.sandiego.ncr.com, or
Ft. Collins,  Colorado              ncr-fc!mikemc@ccncsu.colostate.edu, or
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dhepner@hpisod2.HP.COM (Dan Hepner) (01/19/90)

As long as we're off electronics and onto plexiglass anyway --

Where do you guys buy plexiglass (or any plastic) for a
reasonable price?  The retail places charge more than you
can buy molded plastic for after it's turned into products.

Thanks,
Dan Hepner
dhepner@hpda.hp.com