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In Reply to: RE: CD/ disc scratch repair (not sure if right forum) posted by pictureguy on August 03, 2015 at 23:11:22
I had tried some automotive products that I have quite a bit of experience with using (though not so much on clear plastic) and was surprised that they didnt work well and I think in one case left a murkiness to the plastic.
I dont think this included expressly plastic polish for automotive use - I don't remember now - but I think the formulation has to be specific to deal with the hardness of the surface at hand - an automotive clear coat, for example being harder than the plastic of a CD
Toothpaste is something I saw a lot of reference to on youtube and such but I don;t think I tried it. But I do know most of the info out there had to be nonsense. Many made reference to peanut butter which I don't understand at all
JaroTheWise
Follow Ups:
I have used Meguiar's PastX to good effect. it has never damaged a disk for me.
Dave
I should maybe try again some of the plastic polishes for automotive - as I say I dont recall if I tried expressly plastic polish or just auto body products. Surely it has to be very fine and probably particular to plastic although for plastic headlights and such I have used general products to good effect - I think on those the plastic polish was usually sort of meek
JaroTheWise
I suspect that automotive clear coat is harder than the plastic used to coat CDs.
Peanut butter? sounds wacky to me, too. But it IS granular at the smallest level. I doubt that it is hard enough to polish plastic, but who knows?
Some of the tooth pastes MAY be advertised as 'tooth polish' which is where I'd head in my investigation.
Too much is never enough
I think somewhere along the line of this I had asked my dentist about the polishing effect of most toothpaste and he told me in the sense of removing material in order to level, then toothpaste was not polish since it would eat away teeth.
I think it is polish but meant to eat away only surface contaminant on teeth
Google the peanut butter thing - it is out there - I think meant to fill scatches with oil or something?
JaroTheWise
I read your post half a dozen times before I THINK I understand what you meant?
If the polish is HARDER than what is being polished, you CAN end up scratching the surface. The SIZE of the 'chunks' and even the SHAPE of the chunks in the polish matter a LOT.
If the polish is harder than the junk on the surface and SOFTER than the substrate (say, the tooth) than you'll clean the surface and won't touch the tooth. Polished!
Again, I'd experiment with ToothPaste AND a dremel. My dremel comes with some polishing pads AND some of what appears to be jewelers Rouge.
MAYBE something off this page could help.
Too much is never enough
I think you got my meaning right - yes the formal definition of polishing would be to remove imperfections by removing some of the surface and leveling it. Toothpaste is likely formulated to remove contaminants but not strong enough to remove enamel
Dremel is fine but I don't like the fact it is both fast yet at the same time too small to do the whole disc as a disc machine would. Without being careful you could get "patchy" sort of results I would expect - again, not sure if it would matter or not
At least my dremel's lowest speed is 5k rpm
JaroTheWise
Enamel is pretty hard. I'd guess harder than the plastic of a CD.
And yes, a Dremel might be pretty harsh. As a matter of fact, the heat generated by the polishing bonnet even WITHOUT any abrasive / rouge might MELT the plastic or soften and allow surfact imperfections to heal.
A Dremel MAY be best for a single scratch, not an entire disc.
I sort of wish I still had access to a good microscope so I could run some tests.
I worked for YEARS in a fab that made Quartz Crystal Oscillators. I used LOTS of abrasives and by the pound. The 'final polish' was done with Cerium Oxide, which if memory serves was 1/2 micron grit size. But it's been nearly 40 years, so don't hold me to THAT.
Too much is never enough
Come to think of it I have a binocular microscope here that goes up to 80x that I could give a look
I once ground a telescopic reflector glass - 8 inch diameter - which was fascinating as to the precision obtained and of course it was necessary to maintain uniformity of the grind - a concave surface - not too relevant I think to the CD that doesnt require uniformity across it, as long as you have clarity (I think)
But you are right as to the heat issues and such. Dremel abrasion is also interesting in that lower speed with certain grits works better than higher speed in which I think the abrasives start to plane over the material rather than bite into it and level it
JaroTheWise
I'm sure, than, you are aquainted with something called an 'optical flat'. We used it to maintain FLATNESS of certain tooling. Putting the flat on a surface and illuminating with a monochromatic light produced an interference pattern. From this you could determine flatness of the inspected object.
The reason I bring this up? I'll bet $$ that a CD is 'specified' as having a certain surface flatness.
The lens which focuses on the 'pits' has an extremely SHORT depth of field which renders a few of the explanations I've heard for some 'digital problems' absolutely moot.
Now that I think about it, I wish I could still get at some of the goodies I USED to have routine access to. A Macbeth densitometer? Surface Profiler? Optical flat? Even a good 'scope, both micro and oscillo.
Those were the days!
Too much is never enough
I have always been surprised at how well a CD laser can read despite scratching - a level of scratching that would make a telescopic lens or mirror a complete mess.
I also use those cd lens cleaning discs often enough living here in AZ with all the dust. I noticed even before it starts to completely fail then it starts into skipping and pauses etc
JaroTheWise
Objects too far OUT of the focal plane will NOT be seen.
Same reason the dust on your camera lens GENERALLY doesn't interfere with taking a picture.
That's ANOTHER good reason not to abrade / polish (overall) the surface of your CDs. Making that coating thinner brings closer the time when ANY minor imperfection enters the focal plane.
Too much is never enough
yes we used a flat with an interference pattern to measure consistency of the concavity - that it would reveal inconsistency causing lack of sameness in the pattern. I recall my piece turned out well, luckily - but also recall how the method was so precise that you could place your fingertips on the glass for a few seconds and the "bumps" in the pattern would appear where the heat from the fingers caused the surface to expand
Sounds like you should get back some of the instrumentation or express it in building some items in order to express your interest
I did that optics stuff 30 years ago so it has been awhile for me too
JaroTheWise
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