Problems edging Alize stock poly

[annie]

I am a sales rep for a wholesale lab,and a very large account of mine has had serious problems edging Alize Stock Poly lenses. They have done everything possible, along with the laboratory to remedy this problem.
It seems as though the Alize stock poly lenses are so thin and flexible, that shadowy crazing effects in the middle of the lens appear after edging. Sometimes this shadow crazing begins withing hours or a day after edging.
Has anyone experienced this same problem?

[fjpod]

There are many threads on this forum regarding this topic. Do a search. My own personal opinion... Make sure your cutting blade or wheel is SHARP.

[Chris Ryser]

It seems as though the Alize stock poly lenses are so thin and flexible, that shadowy crazing effects in the middle of the lens appear after edging. ?

you just said it..............flexible. The AR coating is a very hard layer of SIO2 which does not seem to like the pressure and the flexing. fipod is probably right, your cutters are working to hard. For a starter change them for new ones.

[For-Life]

Have had this problem and here are the solutions:

1. Make sure the blade and wheel is sharp
2. Always double chuck poly AR
3. Use low pressue
4. Always use a smaller chuck (with a larger chuck it presses against nothing on the other side).

[Pete Hanlin]

What you are experiencing is crazing of the AR coating. This is caused by lens flexure, which causes a "foggy" area to appear on the lens. Listed are the various crazing patterns- along with the usual causes...

With all of these scenarios, keep in mind that the coating is extremely thin and hard (glass-like). While this hardness provides durability and makes the surface less likely to scratch, it is also far less flexible than the substrate upon which it is placed. Sandwich a sponge between two microscope slides, try to bend the stack, and you'll understand the principle at play here...

Straight up and down lines- slightly off center. You will usually note this type of crazing on a frame with a shallow "B" measurement and a long "A." That is, a rectangular or oval frame.
Cause: Improper lens removal from the chuck. Usually, the technician is "peeling" the lens from the chuck- which causes the lens to bend at the edge of the chuck and crazes the coating.
Solution: Optimally, use a pair of deblocking pliers to twist the chuck from the lens. Alternatively, you can use a table-mounted device that allows you to twist the lens from the chuck (but be careful not to apply too much pressure).

Small "dot" (3-5mm diameter) in center of lens. You may notice this type of crazing on any shape lens.
Cause: Excessive chucking pressure. The lens is being compacted from the chucking pressure. On edgers which use air pressure for chucking, attempt to lower the pressure at the chuck (I believe National Optronics has a kit for this purpose). Some edgers provide 2x PSI at the chuck compared to the pressure in the line. So, if you have 60PSI in the line, you are chucking the lens at 120PSI of pressure.
Solution: On newer edgers, use the "fragile" setting on the chuck. Alternatively, ensure plastic chucks are not "compacted," which decreases their sponginess. If using metal chucks, consider sampling flexible chucks.

"Bulls-eye" in center of lens (central dot with ring around it). You may notice this type of crazing on any shape lens.
Cause: Mis-matched chuck and clamp. It is often popular to switch to the "half-eye" chuck or clamp that came with the edger (to avoid grinding into the chuck or block when edging shallow "B" frames). If the chuck and the clamp (the bit that contacts the lens on the other side) are not matched, the clamping pressure is bending the lens around the smaller of the two (either the chuck or the clamp). As a result, a "ring" around the center of the lens is bent, and the coating crazes- since it is less flexible than the substrate.
Solution: Ensure the chuck and clamping device are of even size. Large or small is really irrelevant- they just need to be the same size. If you no longer have matching sizes, contact your edger manufacturer (who may even carry a specific block or clamp-tip for edging AR coated lenses).

Crescent shape off center. You may notice this type of crazing on any shape lens, but it is more prevalent on oval or rectangular frames.
Cause: Torsion while edging. The cutting wheel or blade is dull- therefore, the feed rate is too great for the cutter's efficiency and the lens is flexing during edging.
Solution: Your edger is designed to have an effective cutting surface. The feed rate is calibrated assuming the cutting surface is efficiently removing lens material. Either replace, true, or have the cutting surface evaluated.

I hope these tips are helpful. We have had various laboratories (ranging from small to labs that process 1,000s of pair per day) which have been able to dramatically reduce lens crazing by following these tech tips.

Best regards,
Pete

[Pete Hanlin]

Ah, I forgot to mention... Oversizing can cause crazing as well- often, this will not be apparent until some time after the lenses have been dispensed (especially if the frame and lenses are exposed to excessive heat- like that found on the dashboard of a car or in your typical frame warmer).

Finally, there have been cases when the lens pliers (you know for adjusting the axis when something has been screwed up ;^) are misused. If you are about to sprain your elbow torquing the lens with one of these, you should probably loosen the frame and gently reposition the axis by hand.
:D

[fjpod]

Pete, Thanks for the best, most concise explanation of this problem so far.

[annie]

Thank you for the useful information. My lab will be sending this account the deblocker we use, along with the pads. We too, believe that the problem is the deblocker they are using.

[Pete Hanlin]

No problem! That's my job... Well, it used to be anyway, when I was in charge of Market Quality.

Best of luck with the edging!

[medicalretina]

have them adjust the edging weight to lighter.
some edger have different edging weight adjustments.

gil

[Cherry Optical]

use a table-mounted device that allows you to twist the lens from the chuck

Anybody know a good source for such a device? We currently are using either hand pliers or this device from WECO that kind of pops the lens off. The thing from WECO looks like a turtle if that helps anyone understand what I am talking about.

I know Precision Tools has a new 'automated' finish de-blocker that would fit the requirements. Problem is they want $6,000.000 for it!

Any help would be appreciated.

Adam

[gemstone]

http://www.looktopsi.com/deblocker.php
Blocking Supplies
Part No: 4523 - Hand Held Deblocker
1677U - 3M Bench Mount Deblocker
Description: Deblockers Features: Hand Held Deblocker

• Twist to deblock and block stays in the deblocker
• Works with all metal edger blocks
• Can be used hand held or bench mounted

3M Bench Mount Deblocker

• Works on SemiTech, AIT, Shuron or Coburn blocks

Anybody know a good source for such a device? We currently are using either hand pliers or this device from WECO that kind of pops the lens off. The thing from WECO looks like a turtle if that helps anyone understand what I am talking about.

I know Precision Tools has a new 'automated' finish de-blocker that would fit the requirements. Problem is they want $6,000.000 for it!

Any help would be appreciated.

Adam

[DragonLensmanWV]

Anybody know a good source for such a device? We currently are using either hand pliers or this device from WECO that kind of pops the lens off. The thing from WECO looks like a turtle if that helps anyone understand what I am talking about.

I know Precision Tools has a new 'automated' finish de-blocker that would fit the requirements. Problem is they want $6,000.000 for it!

Any help would be appreciated.

Adam

I got mine from DAC.

[Barry Santini]

Tharcle: You have mail!

Barry

[Barry Santini]

Try using a few drops of "ALL-OFF" between the pad/lens/block...BEFORE you deblock!

Worked for us!

B

[Kyle]

While in a previous post I mentioned our office not having had any problems with lens slippage, I DID have an occasional issue with crazing "spots" about 3 years ago. We followed similar steps to what Pete is suggesting and they worked beautifully:

We're running a 7070SX from Santinelli that had too much head pressure - the "approach", or lens feed, was too aggressive and caused the crazing to appear almost swirled. We backed off on the feed and actually lightly INCREASED clamp pressure from where we had been and BINGO - no problems...

For those who don't already have a proper inspection station it is integral that you have a jet black, low sheen (preferably matte) background with a very bright spot/task light in order to properly inspect your lenses for surface imperfections. A well-illuminated inspection station will help you catch those crazings before they walk out the door.

And Pete, I believe you mistakenly omitted one massively critical point that I'll illustrate for everyone else: frame adjustment.

It's like this: if you cut a 2 base lens bevel and try to fit it into a frame with a 6 base eyewire bevel, you're going to be bending the lens and causing that coating to FREAK OUT. IT AIN'T GONNA WORK, PEOPLE!!! Ever try to bend a painted board? Guess what happens to the paint! Just because you've not noticed a problem with this before doesn't mean it hasn't existed.

Adjust your bevel guide or your frame, whichever is most prudent, so that the two match and you'll not only save your patient from the agony of ridiculously poor optics but also will decrease the likelihood of AR failure!!!!!!!! What good is all that math and science behind birefringence-free aspheric/atoric lenses if you're just gonna treat them like an acrylic demo??? Your patternless edger may be smart enough to figure this out automatically but there's a reason the guided bevel function exists on its hard drive and I can assure you it's not there just to appease us "old schoolers".

Finally, poor bevel matching will cause an almost INSTANT coating failure when the lenses get exposed to any significant heat source, if it even takes THAT. And with respect to Pete and his large lens corporation, you REALLY need to remove ALL AR lenses prior to heating the frame. Lenses are not designed with frame warmers in mind, especially the off-brands and ESPECIALLY the off-brand poly and 167's!

Respect.

Kyle