Sanding, polishing headlights...

[kajaalyo]

Hello,
I`m new to headlight restoration, I did 2 pairs and 1 pair of really big headlights so far.
All of them turned out good, except there is on thing that really bothers me.
Headlights look like new, but if I look really close, under the correct angle I can see fine straight (usually horizontal) scratches, really fine, can`t even see them on beam with headlight turned on.
There is no point of uploading a photo, because it`s not visible on the photo...
But it still bothers me...
My process:

Wet sanding:
600 if headlight is really bad, 1000, 1500, 2000
I change directions (horizontal / vertical) each time I change sandpaper so I can see if there are any scratches left behind, once I don`t see any scratches I go another pass just to be sure..
Each time I check for left over scratches on wet and on dry clean headlight...

Polishing:
I have 3m system pads and compounds...
3M Perfect-it III Fast Cut Plus Compound with green pad
3M Perfect-it III Extra Fine Compound with yellow pad
3M Perfect-it III Ultrafina SE Polish with blue pad

I can start to see those tiny scratches when I`m working with fast cut plus, because they are straight I know that they are not made by polishing...
I can work how much I want with fast cut, but they don`t disappear...

Anyway I do 3 passes vertical and horizontal before applying fresh compound, I repeat this 3 times...
Then the same for yellow and blue compounds...

When I was working at Citroen dealer as a mechanic I had opportunity to wach my coworker at body shop xxx times as he was polishing headlights with same 3m system, using same grit sandpaper... he didn`t even use 2000grit and it was always perfect...

I`m not rushing with sanding process, I know that some things can`t be rushed... I really take my time... like 4 hours for a pair of headlights.

Any idea what could be done?
Thank you

 

[Stormin08]

are you using a DA sander to perform this ??? sounds like it is done by hand.

possibly the use of DA will help with straight line defects, as well as using it to polish it out.

what are you protecting them with after ? i dont see the use of a coating or even reapplying a clear coat...both of which could cover the slight defect with a self leveling effect.

 

[Mike PhillipsMike Phillips is verified member.]

Hello,

I`m new to headlight restoration, I did 2 pairs and 1 pair of really big headlights so far. All of them turned out good, except there is on thing that really bothers me.

Headlights look like new, but if I look really close, under the correct angle I can see fine straight (usually horizontal) scratches, really fine, can`t even see them on beam with headlight turned on.


Any idea what could be done?

Is it possible these lines are cracks IN the plastic?

I see this all the time on older cars. I think the term is,

Craze or Crazing



Definition

Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction.


Most of the time when any of us are doing headlight restoration it's on OLDER cars. Thus the plastic is OLD. You don't really see people sanding on headlights on brand new cars. It's the age and stress on the plastic from expansion and contraction over time that causes crazing.

If it is crazing - then the only honest fix is replace the headlights. This is usually too expensive in context of the value of the car so sanding and polishing is performed and whatever you get is better than they were.



Just a guess....

 

[kajaalyo]

are you using a DA sander to perform this ??? sounds like it is done by hand.

possibly the use of DA will help with straight line defects, as well as using it to polish it out.

what are you protecting them with after ? i dont see the use of a coating or even reapplying a clear coat...both of which could cover the slight defect with a self leveling effect.

I'm sanding by hand. I'm looking towards investing in da sander. Is there any device in range around 150 eur and can also be used for polishing? My polisher is good bosh, but not da and it's too big for headlights with 13cm pads...
However I did paint correction on my black astra with it with excelent results. Also it leaves no defects on headlight finish.

I use none abrasive wax to protect them. I know that this is not long term protection and would also like to invest in polymerization kit. Any thoughts on that?

 

[kajaalyo]

Is it possible these lines are cracks IN the plastic?

I see this all the time on older cars. I think the term is,

Craze or Crazing



Definition

Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction.


Most of the time when any of us are doing headlight restoration it's on OLDER cars. Thus the plastic is OLD. You don't really see people sanding on headlights on brand new cars. It's the age and stress on the plastic from expansion and contraction over time that causes crazing.

If it is crazing - then the only honest fix is replace the headlights. This is usually too expensive in context of the value of the car so sanding and polishing is performed and whatever you get is better than they were.



Just a guess....

No it's not the cracks, I can also see those cracks and they look different.
I agree with you. Those cracks are not that visible and there is nothing I can do about it. Anyway it's worth to polish the headlights. But however I want to fix those scrathes, I feel bad returning lights like that to owners... Till now every owner was like "Don't worry about it, my headlights look like new, wow you did a good job.". But I feel bad, I always do mechanic work perfect and would really like to do headlights perfect to.

 

[TTQ B4U]

Hello,
I`m new to headlight restoration, I did 2 pairs and 1 pair of really big headlights so far.
All of them turned out good, except there is on thing that really bothers me.
Headlights look like new, but if I look really close, under the correct angle I can see fine straight (usually horizontal) scratches, really fine, can`t even see them on beam with headlight turned on.
There is no point of uploading a photo, because it`s not visible on the photo...
But it still bothers me...

You're overthinking it and looking for perfection. The cracks you're seeing are likely in the plastic lens itself. They are simply crazing.

My process:

Wet sanding:
600 if headlight is really bad, 1000, 1500, 2000
I change directions (horizontal / vertical) each time I change sandpaper so I can see if there are any scratches left behind, once I don`t see any scratches I go another pass just to be sure..
Each time I check for left over scratches on wet and on dry clean headlight...

Here too, IMO, your doing too much. A single headlight in even bad shape shouldn't take you more than 30 minutes tops. Everyone has their process and that's fine but with plastics, simply stay with 800 to 1000 grit. To go lower is simply creating more work for yourself when it comes to refining them back. I rarely find a need to go below 1000 grit. Use a small rotary and 1000 will cut through even badly exposed plastics pretty fast. Move to 2000 then 3000. On certain ones that are really finicky about finishing out I may go 5000 but usually by that point I'm into the compound and polish phases.

Rolite makes a coarse, medium and fine set of products and are excellent for plastics. Simply make your way through those. Again, here too, you won't need all 3. I rarely need to start with coarse. Polish with medium and fine/ultra fine and from there the last step is a spray clear.

For the final level of gloss and protection there are several options. I use a Meguiar's Spray on Headlight coating. 2 layers and you're done.

The above are just my tips in a truncated opinion. Here are a couple examples using my steps. None of these took over an hour for the pair.

 

[kajaalyo]

You're overthinking it and looking for perfection. The cracks you're seeing are likely in the plastic lens itself. They are simply crazing.




Here too, IMO, your doing too much. A single headlight in even bad shape shouldn't take you more than 30 minutes tops. Everyone has their process and that's fine but with plastics, simply stay with 800 to 1000 grit. To go lower is simply creating more work for yourself when it comes to refining them back. I rarely find a need to go below 1000 grit. Use a small rotary and 1000 will cut through even badly exposed plastics pretty fast. Move to 2000 then 3000. On certain ones that are really finicky about finishing out I may go 5000 but usually by that point I'm into the compound and polish phases.

Rolite makes a coarse, medium and fine set of products and are excellent for plastics. Simply make your way through those. Again, here too, you won't need all 3. I rarely need to start with coarse. Polish with medium and fine/ultra fine and from there the last step is a spray clear.

For the final level of gloss and protection there are several options. I use a Meguiar's Spray on Headlight coating. 2 layers and you're done.

The above are just my tips in a truncated opinion. Here are a couple examples using my steps. None of these took over an hour for the pair.

Very nice. Thank you...
I use so much different grit sandpaper because I'm affraid I will not get perfect result when sanding by hand. I will follow you process and take a look into mentioned products.
What is the finish of this coating like? Does it have orange peel?

 

[Mike PhillipsMike Phillips is verified member.]

But however I want to fix those scrathes, I feel bad returning lights like that to owners... Till now every owner was like "Don't worry about it, my headlights look like new, wow you did a good job.".

But I feel bad, I always do mechanic work perfect and would really like to do headlights perfect to.

Don't feel bad.

Do your best. Educate the customer and call it good.

Remember, if the customer wants perfection, let them know replacement is an option. When they see the price for a new replacement plus the labor for installation - you'll look like a hero.



:cheers:

 

[TTQ B4U]

Very nice. Thank you...
I use so much different grit sandpaper because I'm affraid I will not get perfect result when sanding by hand. I will follow you process and take a look into mentioned products.
What is the finish of this coating like? Does it have orange peel?

You're welcome. Look into using a drill or a small rotary for sure. Hand sand where needed for safety / tight spots. The coating goes on and self levels nicely. No orange peel or texture. Perfect.

 

[burningac1d]

are you using a sander(useful article) to perform this ??? sounds like it is done by hand.

possibly the use of DA will help with straight line defects, as well as using it to polish it out.

what are you protecting them with after ? i dont see the use of a coating or even reapplying a clear coat...both of which could cover the slight defect with a self leveling effect.

I hope that it helps, can you recommend not expensive but effective sander for these cases?