I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

flame polishing is one way to make hazed plastic clear again, but it
depends on what you're working with.

Another way is to use a very dissolvable plastic and dip it in solvent and
let it dry. This works with acrylic and the stuff they make clear
screwdriver handles out of. I seal my name into handles like this with
acetone.

On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott
wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?


cracking is the biggest issue i had doing this. I "made a sandwich"
with AL above and below, clamped together. Don't know all the names
for sure, I think it was called lexan.

Only did it once, but it came out nice on my second try.

karl

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

On 11/5/13, 10:26 AM, Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.


I really have no plastics experience, but once saw some guy cleaning up
(what I think was) plexiglass edges with a propane torch.

It was obvious he'd had a lot of experience doing so, as they came out
smooth, transparent and magically perfect like... he said they called
it 'flame polishing'

Just did a YouTube search and got a bunch of hits, but on time to watch
any now.

BTW, there is a polymer newsgroup... though the time or two I looked
there was nothing but Crickets chirping there.

Good Luck!

Erik

"Tim Wescott" wrote in message
...
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


From what I have read the biggest thing is to get the feed and speed right.
I don't think any method of cutting is going to leave you a perfect finish,
but cutting with feeds to slow for the RPM is going to leave the hard white
stringy melted surface that you hate. I've not done any "clear" plastic,
but I occasionally cut stencils out of PETG photo mounted to a sacrificial
backer. On my little CNC router I turn the spindle speed down to about
18,000 RPM, and scream along with a fresh sharp down cut carbide router bit
at a very high feed. Usually around 100 IPM with my smallest bits and even
faster with larger ones. Since these are usually one offs and not frequent
I have not played with getting it exactly right, but I've found in general
the faster I feed (and the fresher the cutter) the better my finish.

I think my approach would be to define the types of cuts first. Cutting a
stencil is certainly going to be different than cutting a mold, and both
would be different from cutting a part with all outside profile machining.
Then I would wander over to CNCzone and ask some of the sign makers for some
help with the speed/feed for your chosen plastic material.

After you have figured out how to get the best possible cut to begin with
then I would look at ways to improve the surface if desired.

Tangent Mode On

.... And after I had it mostly figured out but before I set it up I would
also consider other approaches for atleast some types of cuts. For instance
if I was making a 3D clear bust I would be more likely to consider making a
mold and selecting a nice casting resin rather than machining the bust
itself out of clear acrylic. I know some folks will freak at that last one
because they are mostly familiar with the thermal issues of thick pours of
epoxy resins (usually not good because most yellow when cured) and most more
common poly resins, but there are resins designed to be poured thicker.
There are also techniques like filling a mold and then emptying it leaving a
thin layer of resin to form a thin shell in the mold.

There are so many other things that can be done when it comes to plastics
and resins that it really depends on what you are making, how it will be
used, and how many of them you need to make. I bet there are even clear
plastics that can be blow molded economically.

Tangent Mode Off

Bob La Londe






---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

Tim Wescott wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

Plexiglas can be polished easily after machining. Jeweler's rouge or
similar stages of roughing and finishing compound, then a final pass with
toothpaste to remove any red tint left behind.

If you want pretty and clear, you can't do better than cast acrylic, it
is as clear as glass, maybe even more so.

Jon

On Tue, 05 Nov 2013 14:21:53 -0600, Jon Elson wrote:

Tim Wescott wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then
make it clear again? Any gotchas? What plastic should one start with?
What question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe),
about 1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01
in all directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

Plexiglas can be polished easily after machining. Jeweler's rouge or
similar stages of roughing and finishing compound, then a final pass
with toothpaste to remove any red tint left behind.

If you want pretty and clear, you can't do better than cast acrylic, it
is as clear as glass, maybe even more so.

Jon

I'm considering casting, although at this point I just want onesies, not
any great quantities.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Tue, 05 Nov 2013 14:29:05 -0600, Tim Wescott
wrote:

On Tue, 05 Nov 2013 14:21:53 -0600, Jon Elson wrote:



If you want pretty and clear, you can't do better than cast acrylic, it
is as clear as glass, maybe even more so.

Jon

I'm considering casting, although at this point I just want onesies, not
any great quantities.

Acrylic stock shapes are available either cast or extruded. The cast
stuff has better optical properties.

As for tough clear plastics, polycarbonate (Lexan) is the most obvious
alternative to acrylic, but more difficult to polish.

--
Ned Simmons

On Tuesday, November 5, 2013 1:26:16 PM UTC-5, Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be

narrowing it down too much.



How hard is it to machine a part out of hard clear plastic and then make

it clear again? Any gotchas? What plastic should one start with? What

question am I failing to ask?





Tim Wescott

Wescott Design Services

http://www.wescottdesign.com

Flame polishing or just polishing.

http://www.harborfreight.com/12-minu...kit-65938.html

Dan

Erik pretended :
On 11/5/13, 10:26 AM, Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.


I really have no plastics experience, but once saw some guy cleaning up (what
I think was) plexiglass edges with a propane torch.

It was obvious he'd had a lot of experience doing so, as they came out
smooth, transparent and magically perfect like... he said they called it
'flame polishing'

Just did a YouTube search and got a bunch of hits, but on time to watch any
now.

BTW, there is a polymer newsgroup... though the time or two I looked there
was nothing but Crickets chirping there.

Good Luck!

Erik

Flame polishing with a small propane or similar torch is fairly easy.
Practice on a scrap first. It is easy to set the edge on fire.

Polycarbonate (Lexan) is NOT suitable for flame polising it bubbles and
cracks.
Acrylic is best.

--
John G

Tim - I drilled the center of a piece of epoxy bar stock about 5/8 in.
thick. Then a brass weight was glued with epoxy to the bottom and a piece
of paper with the scale for a hydrometer was placed inside. Then a thin top
was glued on with the tiniest gooping onto the the first number of the paper
scale. Suprizingly, it looked noticebly better than the others.

Hul

Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:


If you want pretty and clear, you can't do better than cast acrylic, it
is as clear as glass, maybe even more so.

Jon

I'm considering casting, although at this point I just want onesies, not
any great quantities.

No, the stuff you buy in blocks is "cast", not meaning that YOU
do the casting, but the thing is cast to net shape. It is allowed to
set up over some time, and when done right is very clear and uniform.
You can also get extruded acrylic, it is not as clear, and has a slightly
wavy surface. It could be polished after machining, though. But,
the extruded stuff is usually tubes and rods with fairly small cross
sections.

Jon

On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott
wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.
just sand it with progressively finer finishing paper and polish.
Made a couple yoyos with the young french exchange student we had with
us 15 or so years ago out of clear acrylic and they are just like
glass

"Tim Wescott" wrote in message
...
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


If you want the face clear, screw a piece of half inch thick plexi to a
wood covered faceplate, cut a circle, and buff the edge

"Tim Wescott" wrote in message
...
I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?


Use an exceptionally sharp tool with a large nose radius and a material
removal rate that produces a continuous chip.

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Flame polish the edge while it's still spinning in the lathe.

Or use Mcguire's.

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.


Polycarbonate (lexan) is much "tougher" and behaves a lot more more like a
metallic alloy than acrylic (plexiglas) which has mehanical properties
that're more similar to a glass.

"Lloyd E. Sponenburgh" wrote:

You can cut any piece of plastic you can successfully cut, and eventually
get it back to clear that way... but it takes a LOT of labor and time.

This is why the flame polishing or solvent dip polishing are preferred
when you don't need optically perfect surfaces.

Modern acrylics have almost the same durability as polycarbonate (lexan), so, unless you're going to be torturing this, I'd go with the acrylic.

Flame polishing works, but you may have to practice to get it right.

Another option is to sand with grades of emery paper, then do a final polish with jeweler's rouge. You can get small quantites of that in a liquid suspension by buying the liquid CD polishing medium.

eric h fired this volley in
:

Modern acrylics have almost the same durability as polycarbonate
(lexan), so, unless you're going to be torturing this, I'd go with the
acrylic.

Flame polishing works, but you may have to practice to get it right.

Another option is to sand with grades of emery paper, then do a final
polish with jeweler's rouge. You can get small quantites of that in a
liquid suspension by buying the liquid CD polishing medium.


This is _almost_ a silly conversation, except that it's not commonly
known that contact lenses and eyeglasses are turned from cast resin on
lathes.

It doesn't 'come out' clear. It's ground with successively finer
abrasives with mechanized laps... just like any other form of mechanical
lense polishing.

I used to grind telescope mirrors by hand. They don't 'come out' clear,
either... the initial curve is ground with abrasives so coarse you can't
even see through the glass afterwards. Then finer, then finer, and over
again with at least five grades before doing the 'rough' polishing with
something aggressive like Barnesite, followed by 'fine' polishing with
washed rouge.

You can cut any piece of plastic you can successfully cut, and eventually
get it back to clear that way... but it takes a LOT of labor and time.

LLoyd

"eric h" wrote in message
...

Modern acrylics have almost the same durability as polycarbonate (lexan),

Hogwash.

wrote in message ...
Tim - I drilled the center of a piece of epoxy bar stock about 5/8 in.
thick. Then a brass weight was glued with epoxy to the bottom and a piece
of paper with the scale for a hydrometer was placed inside. Then a thin
top
was glued on with the tiniest gooping onto the the first number of the
paper
scale. Suprizingly, it looked noticebly better than the others.

Hul


A good solvent to clean up the interior void would be glacial acetic acid.
It melts the acrylic and then it hardens with a smoother surface. A couple
of droppersfull would do a small volume like this. Must be "glacial"(99%),
not "normal" or vinegar(~5%)

http://www.grainger.com/Grainger/LAB...131107153158:s

The thinnest Weld-on products would work too.

http://www.amazon.com/IPS-Weld-On-Ac.../dp/B000KZUTEM

Stumpy wrote:

wrote in message ...
Tim - I drilled the center of a piece of epoxy bar stock about 5/8 in.
thick. Then a brass weight was glued with epoxy to the bottom and a piece
of paper with the scale for a hydrometer was placed inside. Then a thin
top
was glued on with the tiniest gooping onto the the first number of the
paper
scale. Suprizingly, it looked noticebly better than the others.

Hul


A good solvent to clean up the interior void would be glacial acetic acid.
It melts the acrylic and then it hardens with a smoother surface. A couple
of droppersfull would do a small volume like this. Must be "glacial"(99%),
not "normal" or vinegar(~5%)

http://www.grainger.com/Grainger/LAB...131107153158:s

Just a heads up to anybody using glacial acetic acid- it's really nasty
stuff, mostly due to the vapors. It's more irritating than even strong
ammonium hydroxide solutions. Good ventilation or a respirator is a must,
not a suggestion.

Charlie+ wrote:
On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott
wrote as underneath :

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

Two things that might be of use if you go for acrylic. Little experience
Im afraid practically.
1. I read long ago that you must not use any oil based contact in your
machining or polishing so that includes most polishing (eg. buffing)
compounds, machine oils etc. - it leads to those hairline fractures not
immediately but eventually, especially in stressed areas.
2. Chloroform is a proper solvent for things like perspex. You can make
perfect joints with it, I think. Though not easy to obtain cheaply,
used to be available in chemists here in uk but no longer! ...C+

Tap suggests a mapp torch in this video, but well, they don't make mapp
anymore. video has other tips for acrylic work

http://www.tapplastics.com/product/r...lic_cement/130

On 6/11/2013 2:52 AM, Karl Townsend wrote:
On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott
wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?


cracking is the biggest issue i had doing this. I "made a sandwich"
with AL above and below, clamped together. Don't know all the names
for sure, I think it was called lexan.

Only did it once, but it came out nice on my second try.

karl

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.


I think Lexan is polycarbonate.

I'm not positive what plastics i used to machine. Getting old and stupid. I remember machining (i think acrylic)blocks for gas manifords for medical devices. I had to keep the speed down, to keep the heat down. Have to use oil, not water as I was once told by a boss I had. I did try that that time and it didn't work. Water just beads up. You have to make sure you always have oil on it or else.
I've machined plastic at several shops, different material and always used oil for lathe, mill and thread. It was crystal clear.










On Tuesday, November 5, 2013 12:26:16 PM UTC-6, Tim Wescott wrote:
I was going to say "acrylic", but then I realized that maybe I would be

narrowing it down too much.



How hard is it to machine a part out of hard clear plastic and then make

it clear again? Any gotchas? What plastic should one start with? What

question am I failing to ask?



The part will be cylindrically symmetric (i.e., turned on a lathe), about

1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all

directions. But it would need to be "pretty".



Some plastic that is a bit more rugged in impact than acrylic would be

nice (do they make crystal clear Delrin?) but I can't think of anything

like that which would actually work in this case.



--



Tim Wescott

Wescott Design Services

http://www.wescottdesign.com

On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott
wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

I've gotten pretty good finishes on acrylic (Lucite, Plexiglas, etc.)
using Hangsterfer S-500 coolant mixed about 1:10 with water, eitther
flood or mist. A squeeze bottle or aspirator (like window cleaner
bottles) would probably work pretty well, too.

Here's the result from one of my earliest trials:

http://memweb.newsguy.com/~mphenry/DiskFinished-2.JPG

Sharp tooling helps and you want a fairly fast feed to avoid melting
the chips to each other or the milled surface.

Mike

On Friday, November 8, 2013 11:22:18 PM UTC-5, Glenn B wrote:

I think Lexan is polycarbonate.

Yes, it is.