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When you fix scratched CD, should you rub circularly or not?


pionphil

Question

Here he says get the car polish off in circular motion:

 

 

However I've read other people saying not to do it in circular motion:

 

"People, don't rub in circles. Discs are read in circles so by rubbing in circles you can just create more unreadable patches. Rub from the inside to the outside instead."

a reply to above comment: "Correct but in a spiral not straight out" What does it mean to rub in spiral not straight out? 

 

User fas42 also said: "Definitely not circular!! ... Going from the centre to the edge of disc, back and forth, along a radius, always. Always do it as lightly as possible, enough to get the job done and no more." (From this thread):

 

 

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24 minutes ago, pionphil said:

"People, don't rub in circles. Discs are read in circles so by rubbing in circles you can just create more unreadable patches. Rub from the inside to the outside instead."

 An exception to this appears to be possible when using a glass lens cleaning cloth as often supplied with prescription spectacles by an Optometrist. They can do an excellent job getting rid of the fine mist from deterioration of the discs plastic case, finger marks etc. Just make sure to clean the cloths in boiling water occasionally.. 

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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44 minutes ago, pionphil said:

"People, don't rub in circles. Discs are read in circles so by rubbing in circles you can just create more unreadable patches. Rub from the inside to the outside instead."

a reply to above comment: "Correct but in a spiral not straight out" What does it mean to rub in spiral not straight out? 

 

Definitely, pure radial motion; no circular ... ever! Whatever is meant by spiral, I don't buy it. I have always rubbed in a direction perpendicular to the tracks - do one zone, slightly rotate the disk, do the next zone, etc. This is where patience pays off; be prepared to go over one particular spot many times - until you're happy with it. I have done a particular bad case 3 or 4 times - meaning, soaping off the polishing agent, rinsing it, drying it - and then playing, in each cycle. Perseverance works - also, you can get away with putting a lot of pressure on when polishing, if you really want to get rid of a bad scratch as much as possible - in spite of me saying in the other thread, "as lightly as possible". Wouldn't hurt to have a throwaway CD, to practice on - to see what you can get away with, 🙂.

 

Had a freebie CD, which was played on a CDP after a long, long, long time in hibernation - the laser assembly did a neat job of imitating a LP cutter, digging in some perfect circular grooves as the weary lubricant stirred back to life. ... Well, this will be interesting, I thought ... worked and worked and worked on it - purely in the radial direction ... plays perfectly, 😉.

 

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The logic of this is no different than when polishing/grinding anything. Random motion insures least probability of uneven polish and

damage to surface from contaminants between surface and buffer. Circular motion centered on a radius whose location you change/rotate

in incremental steps is the easiest approximation for human ergonomics. Always assume your polishing buffer is contaminated quickly and

take steps to frequently  clean/swap the surface  used for buffing.

 

 

Regards,

Dave

 

Audio system

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here, its the same thing as grinding/buffing the reflector for a dobsonian telescope. The first few seconds of this video show you orbital polishing on a rotating platform, since most of us don't have this hardware its easier to traverse 1 radius line, rotate enough to start on a second radius line with some overlap of polishing, repeat until done. Think of it as double circular polishing. I used to have a Memorex CD

scratch remover that worked just like the video below by gears and mechanical crank power.

 

 

Regards,

Dave

 

Audio system

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13 hours ago, fas42 said:

 

Definitely, pure radial motion; no circular ... ever! Whatever is meant by spiral, I don't buy it. I have always rubbed in a direction perpendicular to the tracks - do one zone, slightly rotate the disk, do the next zone, etc. This is where patience pays off; be prepared to go over one particular spot many times - until you're happy with it. I have done a particular bad case 3 or 4 times - meaning, soaping off the polishing agent, rinsing it, drying it - and then playing, in each cycle.  

 

 

What do you think about using a compound instead of a polish?

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The easiest way to do it is simple random wiping in lazy, irregular figure-of-8s.  As I said in another post, when I polish small pieces the size of a CD (although I don't polish my CDs), I place the surface to be polished face down on a thick piece of glass (an old shelf or table top will do) with the appropriate cutting compound on it.  I grip it with a suction cup or other "handle" I can hold to wipe it on the surface in random 8s.

 

For most polishing like this, I use valve grinding compound - but you can use automotive scratch removers, toothpaste, flour of pumice, or any other cutting compound you like.  I use a coarser grit first, then work thru one or two finer levels until I get the finish I want.

 

If you have a seriously bad scratch on a CD you can't play and can't replace, you might try filling it with a LOCA (liquid optically clear adhesive). The slow setting ones that use a little UV light to cure can be wiped off if you smear it on the rest of the disc.  Filling the damaged area with optically clear material can often make a disc readable again.  There are some reports of success with petroleum jelly, although I'd imagine this could mess up the bottom of the disc tray unless it's really confined to the scratched area (which would probably be hard to do).

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1 hour ago, pionphil said:

 

What do you think about using a compound instead of a polish?

 

A cutting compound just uses coarser particles in it, to do the "polishing". Which means that fine scratching occurs; which may not be  a problem for the reading device. If it is, and cosmetically it doesn't look good, then you would need to to use a polish as the final step. I've just found that using the finest grade of polish gets the job done; but that it requires more elbow grease - you have to keep going over the worst spots, until it's good enough.

 

Other people have got good results using toothpaste; and @bluesman has obviously very good experience in other techniques - I started using a certain method, and have been happy with it; I wouldn't recommend a practice that I haven't tried myself, but that's only because I'm not comfortable about doing that.

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CD plastic is soft and scratches easily so as davide256 says, clean everything and use new soft cloths, etc. frequently. 

I've always used a radial motion (hole to outside and back) because that makes sense to me given the circular reading pattern.

If I had deep scratches instead of just surface then maybe I'd use some more aggressive media but I've always just persevered with a very fine automotive paint polish. 

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2 hours ago, fas42 said:

If it is, and cosmetically it doesn't look good, then you would need to to use a polish as the final step.

I strongly recommend stopping when the audible problem(s) that made you do this are resolved.  Clean the disc after some rubbing and try to play it.  If it's fine, stop.  If it's not, keep going and check it repeatedly.  If you expose the data layer, the game's over.

 

How the disc looks doesn't matter at all - the only thing that matters is if and how well it plays.

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7 minutes ago, bluesman said:

I strongly recommend stopping when the audible problem(s) that made you do this are resolved.  Clean the disc after some rubbing and try to play it.  If it's fine, stop.  If it's not, keep going and check it repeatedly.  If you expose the data layer, the game's over.

 

How the disc looks doesn't matter at all - the only thing that matters is if and how well it plays.

 

I agree. I can't see getting down to the data layer, though - I have never come across a CD where the damage is so severe that it's getting close to the layer where the pits are.

 

It's on the label side where one has to be ultra careful - this is very fragile; and if a careless fiddling with the disk damages that, then it's impossible to recover.

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8 minutes ago, fas42 said:

It's on the label side where one has to be ultra careful

The laser reads through the bottom surface and reflects off the underside of the delicate metallic layer that's below the label side.  There's no reason to polish or otherwise touch the top surface at all - ever.  As you point out, it is delicate and easily damaged (which is why the best tool for writing on it is a felt tip marker made for the purpose).  Even it it were opaque from fine surface haze or foreign material on the top surface, the disc would still play as long as it's not out of balance.

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I have a CD where the label did fail, over a roundish, nearly 4mm wide patch - the silver layer just flaked off, by itself as far as I'm aware. The CD player didn't like it one bit - almost came to a stop, and had to be coaxed to the next track. What to do?! ... Used EAC to rip it, and, smart software that it is, managed to pull off the data, without reporting an unfixable error - burnt that to a CDR - everyone happy again, especially the CDP, 🙂.

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6 hours ago, GregWormald said:

CD plastic is soft and scratches easily so as davide256 says, clean everything and use new soft cloths, etc. frequently. 

I've always used a radial motion (hole to outside and back) because that makes sense to me given the circular reading pattern.

If I had deep scratches instead of just surface then maybe I'd use some more aggressive media but I've always just persevered with a very fine automotive paint polish. 

What does the label say for a very fine polish? Is there a specific grit? 

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On 1/15/2021 at 4:49 PM, fas42 said:

 I've just found that using the finest grade of polish gets the job done; but that it requires more elbow grease - you have to keep going over the worst spots, until it's good enough.

 

Other people have got good results using toothpaste; and @bluesman has obviously very good experience in other techniques - I started using a certain method, and have been happy with it; I wouldn't recommend a practice that I haven't tried myself, but that's only because I'm not comfortable about doing that.

 

I just tried toothpaste and it just made more scratches. 

There are a lot of different kinds of polish: https://www.amazon.com/s?k=meguiar+car+polish&ref=nb_sb_noss_2

Which one would be the finest grade?

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As far as I can remember I used the Meguiars Clear Coat Safe Polishing Compound with some success.

As I'm a bit of a nut for sharp knives (OK—really seriously crazyx-D) I now have diamond polishing pastes that go down to 100,000 grit or .25 micron, and I use them.

You want something that has some grit in it and not just waxes, and that is designed to give a mirror polish.

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45 minutes ago, pionphil said:

 

I just tried toothpaste and it just made more scratches. 

There are a lot of different kinds of polish: https://www.amazon.com/s?k=meguiar+car+polish&ref=nb_sb_noss_2

Which one would be the finest grade?

 

Okay, the one I started with, and have always been happy with, is

 

https://statewidefastener.com.au/images/uploads/SPGDW375.JPG

It just happened to be the one I grabbed from the shelf - the equivalent in another brand should be fine, I suppose ... lately, it's been hard to find, I was pleased to finally locate a bottle, after the original one was used up.

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1 hour ago, fas42 said:

 

Okay, the one I started with, and have always been happy with, is

 

https://statewidefastener.com.au/images/uploads/SPGDW375.JPG

It just happened to be the one I grabbed from the shelf - the equivalent in another brand should be fine, I suppose ... lately, it's been hard to find, I was pleased to finally locate a bottle, after the original one was used up.

Is that an Australian product? I'm not finding it on Amazon.

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I made a shower splash panel for our master bathroom from a polycarbonate sheet, and my wife whacks it with a hair care product or her comb every once in a while. I've had great success with Novus products.  #2 is probably the best choice for CDs damaged enough to keep them from playing.  #1 is the finest polishing compound but may not be enough for scratches sufficiently severe to impede playback.  And #3 is serious cutting compound that's probably too harsh.

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55 minutes ago, pionphil said:

Is that an Australian product? I'm not finding it on Amazon.

 

Yes, by the Selleys company - they seem very reticent in pushing it at the moment, it's not even on their website. For some bizarre reason, their Malaysian branch does promote it, https://www.selleys.com.my/index.php/car-care/158-diamond-finish-polish.html

 

I would go for an easily available, equivalent local product from another company, myself ...

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25 minutes ago, pionphil said:

If you tried to fix the scratches with just sandpaper only, would it not work as well as a polish or compound?

 

Seems pretty easy to determine using a CD from the thrift store or an unwanted one from your collection...

Sometimes it's like someone took a knife, baby
Edgy and dull and cut a six inch valley
Through the middle of my skull

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6 hours ago, pionphil said:

If you tried to fix the scratches with just sandpaper only, would it not work as well as a polish or compound?

 

The thing about a polish is the liquid base - that moderates the 'scratching' action, and helps keep the temperature down ... huhh? You would be surprised how much of a heat build up occurs, if you do it vigorously enough - on my "worst case", the plastic actually deformed because of the temperature rise.

 

If you really want to try sandpaper, then the finest grades of wet 'n' dry - and do it with the water ... rinse often!

 

As suggested above, grab a dud CD and experiment, is probably the way to start ...

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