Backside scratches after polishing

**marc71** · 04-08-2009, 04:09 PM

Hello,

We recently started having a problem just with poly semi-finished lenses. After the polishing step, we de-block the lenses and they have random, somewhat circular scratches on the backside.

The problem only happens with poly.
We changed the polish (we use universal photonics polish)
We changed the first and second fine pads to all new ones from a new batch
Since the problem only happens with poly (every thing is perfect with Cr-39) this seems to eliminate any issues with the generator or finners and polishers. we even upped the finning time by 30 seconds to no avail.

does anyone have any thoughts?

Thanks!

**Aarlan** · 04-08-2009, 06:34 PM

minor debris in the polish can cause very minor scratches. Try putting a filter (you can try women's stockings or very fine mesh screen)in the drain hose to catch the very small particles.

Also, if the scratches are extremely fine, they should coat over w/ the backside coat.

remember that uncoated poly is awfully prone to scratches, so it isn't suprising that it only happens on this material.

**IC-UC** · 04-08-2009, 06:43 PM

Yeah, small debris could cause an issue. Check your polish time and pressure too.
Is it happening on all Poly, or only certain types or sizes? Could be the larger crib diameters need a longer time in polishing.

But I would try the filter first.

**LilKim** · 04-08-2009, 09:15 PM

Or your polish may be too warm. I would seriously consider investing in a backside spin coater, or farming out your polys and 1.67s to a lab that has the equipment to do so. We have a freestanding one that hooks up to our air lines, with a bucket system in the bottom, and besides an occasional bulb and coat change, it's saved us a ton of money in breakages from bad surfaces. We've been backside coating our AR jobs, finding that the AR lasts longer when we coat them first.

**IC-UC** · 04-08-2009, 11:04 PM

Originally Posted by LilKim

I would seriously consider investing in a backside spin coater, or farming out your polys and 1.67s to a lab that has the equipment to do so.

Isn't it the norm to back side coat the Poly lenses? I would have taken this as a given.
If you are trying to get perfection from Poly without a BSC, then you have a whole lotta trouble on your hands!

**Chris Ryser** · 04-09-2009, 03:11 AM

Originally Posted by IC-UC

Isn't it the norm to back side coat the Poly lenses? I would have taken this as a given.
If you are trying to get perfection from Poly without a BSC, then you have a whole lotta trouble on your hands!

Backside on Poly has to be coated as a must. There is no naked poly lenses..........they scratch when you just look at them. However the polish should per perfect.

**scriptfiller** · 04-09-2009, 12:02 PM

Depending on the depth of the swirl marks, the back-side coating should fill the scratch. We used to do that as our get-out-of-jail-free card with uncut lenses that had a few noticable hair line scratches that would be seen by our accounts.

**chip anderson** · 04-09-2009, 01:47 PM

Now, you be done to got swirl marks or scratches?

**LilKim** · 04-09-2009, 06:08 PM

Where are the swirls at on the lenses? At the edges or the center? If it's consistently one or the other, you have a problem with pulling the wrong tool for surfacing. Pulling too "steep" of a tool will result in the swirls being on the outer edges, and pulling too "shallow" of a tool will get you swirls in the center.

RT · 04-09-2009, 08:14 PM

Where are the swirls at on the lenses? At the edges or the center? If it's consistently one or the other, you have a problem with pulling the wrong tool for surfacing. Pulling too "steep" of a tool will result in the swirls being on the outer edges, and pulling too "shallow" of a tool will get you swirls in the center.

Well, its hard to believe that Marc71 is capable of pulling the correct tool for all materials other than poly, but suddenly goes brain dead when pulling tools for poly.

I think my good friend Aarlan hit the nail on the head--there's something contaminating the polish. The nature of polycarbonate makes it more susceptible to showing a scratch from polish contamination than CR39. Scratches from contaminated polish would look circular, as you described.

Don't overlook the possibility that you are inducing the scratches either through your inspection process, your deblocking process, or your cleaning process prior to backside coating.

**partyoptician** · 04-09-2009, 08:59 PM

WHat type of generator are you using? I had similar problem and the generator needed to be recalibrated. Call your tech support for your generator. Also this may seem silly but double check and make aure your 1st & 2nd fine pads are the same size. I once got shipped the wrong size 2nd fine pad and didn;t catch it until I screwed up a set of polys. The first fine were 3 1/2 and the 2nd fine were ( by mistake) 3. Good Luck.

**edKENdance** · 04-13-2009, 07:49 PM

Originally Posted by marc71

Hello,

We recently started having a problem just with poly semi-finished lenses. After the polishing step, we de-block the lenses and they have random, somewhat circular scratches on the backside.

The problem only happens with poly.
We changed the polish (we use universal photonics polish)
We changed the first and second fine pads to all new ones from a new batch
Since the problem only happens with poly (every thing is perfect with Cr-39) this seems to eliminate any issues with the generator or finners and polishers. we even upped the finning time by 30 seconds to no avail.

does anyone have any thoughts?

Thanks!

Have you checked to see if your coater is working correctly? Cure time etc...

**marc71** · 04-13-2009, 08:30 PM

I appreciate everyones help. To clarify, the scratches are prior to hard coating. We use an ultra optics coater and the scratches almost always come out after hard coating. We have tried everything including changing polish pads and polish. On the finning side, we have changed finning pads and the filters. Tomorrow we will try 3 stepping poly to see if maybe that makes a difference since I believe we've narrowed it down to the finning stage.

any other thoughts are greatly appreciated.

Thanks!

**edKENdance** · 04-13-2009, 08:31 PM

OK, this one is a little out there. Untrued laps?

**gemstone** · 04-13-2009, 08:46 PM

Originally Posted by marc71

I appreciate everyones help. To clarify, the scratches are prior to hard coating. We use an ultra optics coater and the scratches almost always come out after hard coating. We have tried everything including changing polish pads and polish. On the finning side, we have changed finning pads and the filters. Tomorrow we will try 3 stepping poly to see if maybe that makes a difference since I believe we've narrowed it down to the finning stage.

any other thoughts are greatly appreciated.

Thanks!

If you follow a couple through, you will likely see little wads of poly 1-1,5 mm on the second fine pad after fining.(That coinside with the position of the swirls on the lenses.) Filter or do not recircurlate fining water. I think PSI may have some additives to help. Keep trying different pads 'til this does not happen. If you allow your polishing guys to deblock after inspecting for scratches, with the minset that coating will fix the problem, it will get worse to the point that the coating will not be a solution. It's a ***** of a problem, but stay with it until you whip it. Not a thing to do with the laps long as they are clean befor the start of cycle.

**edKENdance** · 04-13-2009, 08:51 PM

Originally Posted by gemstone

If you follow a couple through, you will likely see little wads of poly 1-1,5 mm on the second fine pad after fining.(That coinside with the position of the swirls on the lenses.) Filter or do not recircurlate fining water. I think PSI may have some additives to help. Keep trying different pads 'til this does not happen. If you allow your polishing guys to deblock after inspecting for scratches, with the minset that coating will fix the problem, it will get worse to the point that the coating will not be a solution. It's a ***** of a problem, but stay with it until you whip it. Not a thing to do with the laps long as they are clean befor the start of cycle.

Are your scratched lenses on power?

**gemstone** · 04-13-2009, 09:02 PM

Originally Posted by edKENdance

Are your scratched lenses on power?

Sorry Ed, I was replying to marc71's question about swirly scratches on poly. It would be obvious that the "somewhat circular scratches on the backside" would be from an occurance on the surfacing machines if the circles match the stroke orbit and pattern of the machine.

**gemstone** · 04-13-2009, 09:06 PM

Originally Posted by edKENdance

Are your scratched lenses on power?

If it's just poly, could be (outside chance) they use different laps for poly. Maybe the poly pads leaving glue spots on the laps. Glue ******s under the pad could make a swirl problem. This is an unlikely possibility. Can't say boogers? Anyway, most likely in the AM he will see little wads of poly build up on his fining pads riht where the swirls are.

**edKENdance** · 04-13-2009, 09:12 PM

Originally Posted by gemstone

If it's just poly, could be (outside chance) they use different laps for poly. Maybe the poly pads leaving glue spots on the laps. Glue ******s under the pad could make a swirl problem. This is an unlikely possibility. Can't say boogers? Anyway, most likely in the AM he will see little wads of poly build up on his fining pads riht where the swirls are.

Different laps for poly? That's not something I'm familiar with. Different pads sure.

**gemstone** · 04-13-2009, 09:18 PM

Originally Posted by edKENdance

Different laps for poly? That's not something I'm familiar with. Different pads sure.

Yes, very unlikely that's the problem.

**Bob MacNeil** · 04-13-2009, 09:30 PM

Stock removal in polishing is critical with poly, it's what removes the scratches from the fining process. Consider spindle speed, lens sweep, clamp pressure and cycle timers. Stock removal in polishing should be 0.03m/m, for what it's worth!

Bob

**edKENdance** · 04-13-2009, 09:37 PM

Originally Posted by Bob MacNeil

Stock removal in polishing is critical with poly, it's what removes the scratches from the fining process. Consider spindle speed, lens sweep, clamp pressure and cycle timers. Stock removal in polishing should be 0.03m/m, for what it's worth!

Bob

Because I'm curious. What is stock removal?

**Bob MacNeil** · 04-14-2009, 11:16 AM

Stock removal is the amount of lens material removed during the surfacing process, for generating and fining, it's done with a dial indicator, in polishing, it's calculated by weight reduction in 0.001 of a gram. (the lens and chuck must be dry)

Bob

**edKENdance** · 04-14-2009, 01:07 PM

Originally Posted by Bob MacNeil

Stock removal is the amount of lens material removed during the surfacing process, for generating and fining, it's done with a dial indicator, in polishing, it's calculated by weight reduction in 0.001 of a gram. (the lens and chuck must be dry)

Bob

Ah, didn't know it by that name.

**marc71** · 04-15-2009, 08:04 PM

Ok, I don't want to get too excited but I think we've solved the problem. When we called the manufacturer they asked if we adjusted the pressures. We were running at 20psi on both finning steps and polishing for poly. we changed to 16psi, increased the second fine from 1:30 to 2:00 minutes and increased the polish time from 5 minutes to 6 minutes. This seems to have worked. It was the end of the day so we will see more tomorrow but hopefully that will do the trick.