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Grinding acrylic


#1

Can somebody tell me what’s the best tool (on my flex shaft) to grind
and shape acrylic (plexiglass)? I’ve been looking in the Rio Grande
catalog but I’m confused by the choice: 3M Flex diamond bands,
sanding bands, Foredom Grinding Stones, heatless wheels, AdvantEdge
Green Silicon Carbide points, diamond Burs, … . Help ! Thank you, Linda


#2

Rio Grande is very helpful in answering questions about things they
sell. Why not ask them?


#3

Linda: Carbide burs followed by sander bands of various grits
followed by a wet pumice polish followed by a tin oxide polish. At
least this works for dentures (grin) Mike Lone Star


#4

Linda: You can use a flexshaft and basic sanding attachments and
grinding burrs and grinding rocks.Or you can use hand tools as well.
Files and sand paper. There are two very important things to remember.
1.Work at slower speeds so the tools don’t load up and the plexi
doesn’t start to melt. 2.Also be aware that plexi-glas gives off a
toxic vapor when sanded. Use an organic vapor mask and good
ventilation if you are going to be working with plexi-glas. Frank Goss


#5

Linda re grinding acrylic, In times past I have made very nice stands
for my jade carvings from acrylic rod contoured to fit individual
pieces.

I found that metal burrs in various shapes and sizes were the best
option for the shaping process. If you use anything that does not
have teeth or serration on the work face it will clog up.

I smoothed the work with a hard mop using a coarse tripoli type
abrasive, ( the name escapes me ) and then achieved a very good
finish with tripoli.

Worked for me, I hope it does for you.

Keith Torckler, Cornwallis, new Zealand


#6

Personally, I use burrs for the roughing cuts. I try to find burrs
that have teeth spaced far apart. The thing you have to remember
about cutting plastic of any type is that it melts. You want to use
a tool which will remove material without melting it. I would stay
away from anything that is going to tend to clog, like diamond burrs
and heatless wheels. Also, you can use sanding drums, but I would
only recommend them for finishing, not roughing out. Even with the
burrs, you have to watch your speed. The faster your bit is spinning
when it touches the plastic, the more likely
you are to melt instead of cut.


#7

Any cutting of acrylic (plexiglas/perspex) whether using a toothed
cutter or an abrasive, will be far more efficient done wet rather than
dry. Tap water is a great coolant/lubricant for this purpose.

When using a bur, saw or drill, try to do the work under water or
have water drip onto the work area. Sanding will also produce
excellent results using “wet or dry paper” under these conditions.

Hope this helps,
Ray Grossman
Ray Grossman Inc.
Manufacturers of Jump Ringer


#8

Hi Linda, While I don’t use plex for jewelery, I do form and shape it
with a combination of tools. The one thing that you will find is that
speed is a problem as it melts the plastic (the faster the speed you
use!). Carbide or High Speed Steel burs work for me with my Fordom,
However it’s hard to keep the speed down to a slow crawl! Coarse Belt
Sanders work for me also, the edges melt a little and I have to file
off the melted edges to finish the them. Most wood working ans/or
metal working tools will work for the Plex! Shaping and drilling with a
router and/or drill press work for me as I’m making small tables. The
legs are made from Acrilic tubing! However I find that using “End
Mills” in the drill press work better than Drill Bits with a hand
drill. If I haven’t answered your questions or you need more
contact me offline and I’ll do my best! GL


#9

There have been, I am sure, hundreds of people working successfully
with acrylic who ignore this fact but as you work and carve acrylic
you set up internal stress that is supposed to be relieved by
annealing, not as in metal with a torch but with a kiln. The more
rotary equipment you use the greater the stress so the more work you
can do by hand the better. If you are only using the white or the
black, you might want to switch to Delrin.

If you are using clear acrylic, the greatest stress impact may come
when you use an adhesive to attach the acrylic or when you polish.
The stress can make the joints craze. It can also make the areas
around any drilled holes crack in radiating patterns. For
thermoformed plastics the same thing can happen.

That said, a rotary rasp works well. You can get them at a hardware
store. (Make sure the shanks will work in you flex shaft or use these
in a drill press). Manual rasps also work on flowing organic forms.
For small places, ball and cone burs can do the trick. Most silicone
wheels will leave residue on the piece, as it is hard to use them at a
slow enough speed where they won�t �burn� into the plastic. Take the
finished piece down to 600 silicon carbide for a smooth finish.
Sandblasting as a surface finish works too. For a wonderful tactile
quality, pumice the acrylic. If you need a glossy finish, polish
slowly and carefully (minimal pressure) with a new buff and clean
white diamond or Zam.

The annealing process for acrylic is long and tricky. I haven�t done
it in a long while but I remember a 12-hour cycle with a soak temp of,
I think, 90 degrees. There is a shorter cycle for plastics, which
haven�t been thermoformed (don�t have to worry about the �memory� of
the material). Rohm and Haas or Dupont will have the specific
annealing

Linda M


#10

G’day; Linda Moughener mentioned that almost any work done on what
we call Perspex and you call Lucite, which are the same acrylic
plastic, will cause strain in the plastic, and recommends oven heating
at around 90�C to help reduce this. Do remember that at much above
this temperature the plastic softens, and at around 150 -200�C it
becomes almost like rubber, but returns to the hard state on cooling,
and will retain it’s hot shape if cooled rapidly under water whilst
under restraint. I have made 10 inch hemispheres of it and stuck them
together to produce molecular crystal models for lecture audiences of
300. They were made by clamping the hot sheet over a hole in an
airtight box, withdrawing the air with a lab water driven vacuum pump
and cooling with a jet of cold air. I used to use chloroform liquid
to join the hemispheres and resultant ‘atoms’ together. When I had to
polish acrylic I used hand-held abrasive papers, well lubricated with
plain water, finally followed with common or domestic metal polish on
a rag - gives a brilliant polish by hand very quickly.

To repolish 800mm square sheets used to make display covers, I used a
very slow speed electric drill holding lambswool buffs - yes - and the
metal polish. Edges were filed round, sanded down, finally with 400grit
papers, then polished with the metal polish. If you want to make the
strains in transparent acrylic visible, take the lenses from a pair of
Polaroid glasses, hold one against a diffuse light source, put the
other one a little distance from it, rotate it until you see no light
through the two and place the plastic between them. The strains will
show up in glorious black and white. Put a piece of cellophane between
the Polaroids and the strains will show up in complementary colour;
magenta, cyan and yellow. the colour denotes the amount of strain.
You may have to hunt around for cellophane of the exact required
thickness, (Called a quarter wave plate) but then you have made an
expensive polariscope. Bravo! The kids would love to make one for
you. If you feel like it, bend a strip of acrylic between the
’crossed’ Polaroiods, and you can see which colour denotes the most
strain. Works for glass too. Lotsa fun and cheers, – John Burgess;
@John_Burgess2 of Mapua Nelson NZ