CDROM metal stripper

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

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

You'd do better to buy one of the books on this from Lindsay

like

He has books showing how to build such parts.

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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

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

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

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

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

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

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[...]

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. formatting link
   and
   formatting link
   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

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||

Sierra Community College, Rocklin CA.

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

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.

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

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Posted via a free Usenet account from http://www.teranews.com

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

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

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

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

Cost. Cost. Cost.

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

Jim

Your arrangement was clear, but my response to John wasn't. I was fixated on the parasitics, and hence the capacitance of the metallizations through two layers of CDROM material was what interested me.

I measured this, and I get 133pF +/- 10pF. That's for two full- circle aluminum-foil plates separated by two CDROMs.

So, you're not off. Neglecting airgaps, half-plates at 1/20th the distance, through mylar, should give about 10x that value, or 1.3nF.

Best, James Arthur