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CDROM metal stripper

  • Thread starter RST Engineering \(jw\)
  • Start date
R

RST Engineering \(jw\)

Jan 1, 1970
0
I plan on using two junk CDROMs in my basic science class as a variable
capacitor for a crystal set -- shim brass cut to cover a little less than
half of each cdrom, glued to the surface, with a vinyl grommet in the middle
to hold the disks together and a disk of mylar cut from a sheet protector
between the brass plates as the dielectric.

Each student is going to have to prepare two disks each, so it isn't a
onesie-twosie job. I need a method that I can use fifty times a semester
every semester.

The problem is removing the metal "plates" that are there now. First
thought was to soak the disks in drano or aqueous lye and dissolve the
aluminum, but further reading and experimentation shows this isn't quite
enough. Apparently there is a lacquer or epoxy coating over the aluminum
and a nickel flash under the aluminum. This is only hearsay, but I know
from experimentation that a caustic solution by itself isn't enough.

Anybody KNOW what the various layers are on the disk and any suggestions on
how to remove them without destroying the plastic of the disk itself?

Jim
 
P

Phil Hobbs

Jan 1, 1970
0
RST said:
I plan on using two junk CDROMs in my basic science class as a variable
capacitor for a crystal set -- shim brass cut to cover a little less than
half of each cdrom, glued to the surface, with a vinyl grommet in the middle
to hold the disks together and a disk of mylar cut from a sheet protector
between the brass plates as the dielectric.

Each student is going to have to prepare two disks each, so it isn't a
onesie-twosie job. I need a method that I can use fifty times a semester
every semester.

The problem is removing the metal "plates" that are there now. First
thought was to soak the disks in drano or aqueous lye and dissolve the
aluminum, but further reading and experimentation shows this isn't quite
enough. Apparently there is a lacquer or epoxy coating over the aluminum
and a nickel flash under the aluminum. This is only hearsay, but I know
from experimentation that a caustic solution by itself isn't enough.

Anybody KNOW what the various layers are on the disk and any suggestions on
how to remove them without destroying the plastic of the disk itself?

Jim
If you use CDRs, you can usually delaminate the coatings by flexing the
disc a few times. Peeling with strong tape is another possibility.

Cheers,

Phil Hobbs
 
D

D from BC

Jan 1, 1970
0
I plan on using two junk CDROMs in my basic science class as a variable
capacitor for a crystal set -- shim brass cut to cover a little less than
half of each cdrom, glued to the surface, with a vinyl grommet in the middle
to hold the disks together and a disk of mylar cut from a sheet protector
between the brass plates as the dielectric.

Each student is going to have to prepare two disks each, so it isn't a
onesie-twosie job. I need a method that I can use fifty times a semester
every semester.

The problem is removing the metal "plates" that are there now. First
thought was to soak the disks in drano or aqueous lye and dissolve the
aluminum, but further reading and experimentation shows this isn't quite
enough. Apparently there is a lacquer or epoxy coating over the aluminum
and a nickel flash under the aluminum. This is only hearsay, but I know
from experimentation that a caustic solution by itself isn't enough.

Anybody KNOW what the various layers are on the disk and any suggestions on
how to remove them without destroying the plastic of the disk itself?

Jim

Brainstorming ideas:
* Use orbital sander or try a scraper.
* Sandblasting
* Microwave the disk..this will create breaks in the coatings allowing
NaOH to attack the Al
* Drop the CD idea ...Buy poly carbonate sheets at the hardware
store... (lexan)...Get it laser cut to any shape..
D from BC
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
Neither trick works with the Verbatim junkers I just played with, but thanks
anyway. How "strong" does the tape have to be? All I used was plain old
clear packing tape for one try and a really stuck-on paper label for
another.

Jim
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
D from BC said:
Brainstorming ideas:
* Use orbital sander or try a scraper.

Labor intensive. Getting 50 kids to sand two disks apiece will either take
a lot of sanders or a lot of time.
* Sandblasting

School doesn't have a sandblaster.
* Microwave the disk..this will create breaks in the coatings allowing
NaOH to attack the Al

THAT was a hell of an idea ...fireworks city, but if you only do it for five
or ten seconds that just might work. It sure as hell crazed the surface.
I'll drop it in the lye bath and report back...
* Drop the CD idea ...Buy poly carbonate sheets at the hardware
store... (lexan)...Get it laser cut to any shape..

You wanna explain to the taxpayer why we have a $50 variable capacitor in
our $5 crystal set?

Jim
 
R

Rich Grise

Jan 1, 1970
0
I plan on using two junk CDROMs in my basic science class as a variable
capacitor for a crystal set -- shim brass cut to cover a little less than
half of each cdrom, glued to the surface, with a vinyl grommet in the middle
to hold the disks together and a disk of mylar cut from a sheet protector
between the brass plates as the dielectric.

Each student is going to have to prepare two disks each, so it isn't a
onesie-twosie job. I need a method that I can use fifty times a semester
every semester.

The problem is removing the metal "plates" that are there now. First
thought was to soak the disks in drano or aqueous lye and dissolve the
aluminum, but further reading and experimentation shows this isn't quite
enough. Apparently there is a lacquer or epoxy coating over the aluminum
and a nickel flash under the aluminum. This is only hearsay, but I know
from experimentation that a caustic solution by itself isn't enough.

Anybody KNOW what the various layers are on the disk and any suggestions on
how to remove them without destroying the plastic of the disk itself?

I just took an old Philips that I've been using for a coaster, and just
scraped some of the top layer off, and imagine my surprise when there
was nothing else there - the rest of the CD was transparent. I was
kinda surprised - I always assumed that the data stuff would be on
the LED side, but apparently the LED sees through the plastic, and the
data is on the underside of the label.

So maybe some 100 grit wet sandpaper?

Good Luck!
Rich
 
D

D from BC

Jan 1, 1970
0
Labor intensive. Getting 50 kids to sand two disks apiece will either take
a lot of sanders or a lot of time.


School doesn't have a sandblaster.


THAT was a hell of an idea ...fireworks city, but if you only do it for five
or ten seconds that just might work. It sure as hell crazed the surface.
I'll drop it in the lye bath and report back...


You wanna explain to the taxpayer why we have a $50 variable capacitor in
our $5 crystal set?

Jim

Maybe after the microwave, the disk might be easier to scrape instead
of doing the NaOH bath..
Also..I'm not sure about this but..the bubbling NaOH provides a
lifting action so any form of damage to the coating might work.
By microwave or scratching by sanding (say 80 grit).
Heck...just grazing the surface with a single scratch might even
work.. The NaOH bubbles may flake/erode the film until there's no
metal..

Also, CDR peeling was mentioned..
One time I got a bad HP CDR and I was able to peel off 60% of the film
by hand.
D from BC
 
J

Joel Kolstad

Jan 1, 1970
0
Jim,

Can you tell us where you're teaching?

How'd you manage to convince the teachers' union to let an engineer teach a
class? :)

---Joel
 
H

Homer J Simpson

Jan 1, 1970
0
I just took an old Philips that I've been using for a coaster, and just
scraped some of the top layer off, and imagine my surprise when there
was nothing else there - the rest of the CD was transparent. I was
kinda surprised - I always assumed that the data stuff would be on
the LED side, but apparently the LED sees through the plastic, and the
data is on the underside of the label.

Sure. There's a molded polycarb 'plate' with the pits on top covered by
metallizing, varnish and paint.


--
..

--
..
..
..
..
..
..
..
..

--
 
J

James Waldby

Jan 1, 1970
0
I plan on using two junk CDROMs in my basic science class as a variable
capacitor for a crystal set -- shim brass cut to cover a little less than
half of each cdrom, glued to the surface, with a vinyl grommet in the middle
to hold the disks together and a disk of mylar cut from a sheet protector
between the brass plates as the dielectric.

Each student is going to have to prepare two disks each, so it isn't a
onesie-twosie job. I need a method that I can use fifty times a semester
every semester.

The problem is removing the metal "plates" that are there now. [...]
Anybody KNOW what the various layers are on the disk and any suggestions on
how to remove them without destroying the plastic of the disk itself?

1. Have you verified that you need to remove anything? I.e., maybe they
will work as-is, since you aren't connecting to the conductive reflective
aluminized layer anyway.

2. Five seconds in a microwave will disrupt much of the conductive layer.

3. http://www.cdmediaworld.com/hardware/cdrom/cd_dye.shtml
and http://www.ccssinc.com/cdr_dye_explained.php have a little diagram
that shows CD and CDR structure. Probably lots of other sites too.

4. Packs of 25 and 50 CDR's come with a clear disk (like a CD with no
metalization) at each end; if you know anyone who goes thru lots of
media, ask them to save those up for you.

-jiw
 
J

James Arthur

Jan 1, 1970
0
If the CDROMs are just there to support the brass plates--with the
mylar dielectric in the middle--why not just face the intact
metallized sides outward, whereby the large gap will minimize any
affect on total capacitance?

Namely, in cross-section: (view using Courier font)

.. ||xxxxxxxxx #### mmm #### xxxxxxxxxx|| <--aluminized layer
.. \_________/ \__________/ facing outward
.. CDROM CDROM
.. B M B
.. r y r
.. a l a
.. s a s
.. s r s

If the resulting minimum capacitance is acceptable it'll save a lot
of effort stripping.

Best,
James Arthur
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
Joel Kolstad said:
Jim,

Can you tell us where you're teaching?

Sierra Community College, Rocklin CA.

How'd you manage to convince the teachers' union to let an engineer teach
a class? :)

Simple. I'm the VP of the freakin' union local and a statewide union
officer as well {;-)

Jim
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
Well, the math isn't difficult. The plates (half-round on a CDROM) have an
area of about 9 square inches (which makes the whole CDROM surface about 18
sq in). If I use a 5 mil mylar (er = 2 or thereabouts) sheet between the
plates and some reasonable estimation of the air gap, I come up with a
fully-meshed capacitance of about a nanofarad.

Polycarbonate has an er of 3, and the CDROM plates are about 50 mils thick.
The capacitance of the brass plate to the aluminum surface is something on
the order of 150 pf, and the capacitance from the outside of one of the
aluminum surfaces to the other is about the same. So, 3 150 pf capacitors
in series has a plate-to-plate capacitance of 50 pf. Compared to 1000 pf of
the meshed plates, that's not a whole lot, but there will be fringing and
all of that stuff, so the more we can keep the strays at bay, the better I
like it.

Besides, the kids can see inside the capacitor and can have a feel for what
happens when the plates rotate with respect to each other.

Jim
 
D

DaveM

Jan 1, 1970
0
RST Engineering (jw) said:
Labor intensive. Getting 50 kids to sand two disks apiece will either take a
lot of sanders or a lot of time.


School doesn't have a sandblaster.


THAT was a hell of an idea ...fireworks city, but if you only do it for five
or ten seconds that just might work. It sure as hell crazed the surface. I'll
drop it in the lye bath and report back...


You wanna explain to the taxpayer why we have a $50 variable capacitor in our
$5 crystal set?

Jim


My $0.02 USD worth...
Here's an idea that came to me as I was opening a new spindle bulk pack of
DVD-RW disks. On the top and bottom of each spindle is a very clear spacer of
the same dimensions of the DVD blanks. No metallization, no printing... just
clear (I assume)polycarb.
My thinking is for the OP to contact some of the bulk CDR suppliers and see if
they can sell a multiyear supply of these spacers. No pain, no chemicals, no
burning plastic. And the price should be right... maybe a few pennies apiece.
I did a cursory Google search, but didn't see any of these spacers listed on any
of the bulk suppliers' web sites, but you gotta know that they have them or can
get them.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some days you're the dog, some days the hydrant.
 
J

john jardine

Jan 1, 1970
0
James Arthur said:
If the CDROMs are just there to support the brass plates--with the
mylar dielectric in the middle--why not just face the intact
metallized sides outward, whereby the large gap will minimize any
affect on total capacitance?

Namely, in cross-section: (view using Courier font)

. ||xxxxxxxxx #### mmm #### xxxxxxxxxx|| <--aluminized layer
. \_________/ \__________/ facing outward
. CDROM CDROM
. B M B
. r y r
. a l a
. s a s
. s r s

If the resulting minimum capacitance is acceptable it'll save a lot
of effort stripping.

Best,
James Arthur

Was just thinking that myself but am calcing about 50pF max across the
variable capacitor but a constant 30pF in the parasitic shunt paths
(100-50-100).
Suggests something like a 40 to 80pF variable cap.
Better still and in the interests of science (i.e. the bits were at hand),
spent 5 minutes making one. (the grommet idea works well).
Min C=64pF, Max C 102pF.
But with finger pressure making the adjusment results in 88pF to 330pF
john
 
M

Michael A. Terrell

Jan 1, 1970
0
RST Engineering (jw) said:
I plan on using two junk CDROMs in my basic science class as a variable
capacitor for a crystal set -- shim brass cut to cover a little less than
half of each cdrom, glued to the surface, with a vinyl grommet in the middle
to hold the disks together and a disk of mylar cut from a sheet protector
between the brass plates as the dielectric.

Each student is going to have to prepare two disks each, so it isn't a
onesie-twosie job. I need a method that I can use fifty times a semester
every semester.

The problem is removing the metal "plates" that are there now. First
thought was to soak the disks in drano or aqueous lye and dissolve the
aluminum, but further reading and experimentation shows this isn't quite
enough. Apparently there is a lacquer or epoxy coating over the aluminum
and a nickel flash under the aluminum. This is only hearsay, but I know
from experimentation that a caustic solution by itself isn't enough.

Anybody KNOW what the various layers are on the disk and any suggestions on
how to remove them without destroying the plastic of the disk itself?

Jim


Why not use thin fiberglass PC boards? Etch the plate areas you
want. Another approach is the old "Book Capacitor", or a homemade
piston trimmer capacitor.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

James Arthur

Jan 1, 1970
0
Was just thinking that myself but am calcing about 50pF max across the
variable capacitor but a constant 30pF in the parasitic shunt paths
(100-50-100).
Suggests something like a 40 to 80pF variable cap.
Better still and in the interests of science (i.e. the bits were at hand),
spent 5 minutes making one. (the grommet idea works well).
Min C=64pF, Max C 102pF.
But with finger pressure making the adjusment results in 88pF to 330pF
john

Dang, actual data! Good show. But, I calculate/estimate the
capacitance of two full-disc plates through two CDROMs (two
thicknesses of 1.3mm polycarbonate, dielectric coefficient=2.9) as:

k * e0 * A 2.9 * 8.85e-12 * pi * (0.060m)^2
C = ---------- = ------------------------------ = 112pF
d 2 * 1.3e-3 m

so this real-world result bugs me.

Hmmm. Why wonder when you can measure? I must try it.

Cheers,
James Arthur
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
That wasn't my battle plan. My idea was to have the polystyrene "platters"
simply there to have a place to glue the plates onto.

The plates themselves are on the INside of the disks with a thin sheet of
plastic (kitchen wrap, saran wrap, a sheet protector cut in half...) between
them. Something like this, and an ASCII artist I ain't:

@@ grommet through the center hole
******************* top cdrom disk
--------- brass shim stock glued to top disk
=================== thin plastic dielectric
--------- brass shim stock glued to bottom disk
******************* bottom cdrom disk
@@ grommet coming through from top



James Arthur said:
Dang, actual data! Good show. But, I calculate/estimate the
capacitance of two full-disc plates through two CDROMs (two
thicknesses of 1.3mm polycarbonate, dielectric coefficient=2.9) as:

k * e0 * A 2.9 * 8.85e-12 * pi * (0.060m)^2
C = ---------- = ------------------------------ = 112pF
d 2 * 1.3e-3 m

so this real-world result bugs me.

Hmmm. Why wonder when you can measure? I must try it.

I calculate somewhere between 500 and 1000 pf for the capacitor with 3 mil
mylar and a 3 mil airgap allowance on both top and bottom plates.

I'm sort of curious why I was off nearly an order of magnitude from the
experimental results.

Jim
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
Michael A. Terrell said:
"RST Engineering (jw)" wrote:
Why not use thin fiberglass PC boards? Etch the plate areas you
want. Another approach is the old "Book Capacitor", or a homemade
piston trimmer capacitor.

Cost. Cost. Cost.

But the last two sound interesting if I can figure out a cheap method of
implementation.

Jim
 
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