HELP SWIRL MARKS IN CR-39 FT's

[APV Optical]

Any one with suggestions. Most of my work consist of specialty, Trivex, Polarized, Poly, anything but the norm. We just had a new account get on board, however they are one of our only uncut accounts, meaning, here come the cr-39 ft-28's by the ton, which Im not complaining but the craziest thing happens. Upon inspection 9 times out of 10 the lenses have swirl marks and have to be re ran. This happens with lenses that we use our own llaps with. What we have been doing is making foam laps when we re-run them and they come out great. Now you would think Humm maybe the laps need to be re-trued. but it is happening to often only on theses lenses. All and seriously all of the others are coming out fantastic. This is all powers not just high cyls or prism. Even -.50 sph. Its really got me stumped and I have been swamped so its just easier to say just make a tool and we will figure it out" but this is adding up. Thanks in advance for any help

[Steve Machol]

Maybe it's the fining pads and polish. What are you using?

[JRS]

Or an aggresive Poly formulated polish. Or both. Or no filtration and he's picking up hairlines that he would not notice in Poly or Trivex.

[Billy Brock]

had the same thing happen back in the old days with cr-39 ......... one time contamination in our slurry ......... one time defect polish from mfgr

this blows my mind that a new lap solves your problem ? ? ? .......hope you find the solution quickly.... be sure to post the results


B

[Jeff Trail]

Chris,


I would agree with JR and Steve, you have to do an elimination of factors here.. you are not using the same pads for all those materials are you? If you are the grit for poly and trivex are more agressive than for CR39.. You can use the same type of slurry (polish) but you need to check and see if the polish you are using is for a combination of all these materials.
Also you may need to check your air pressure and run time on the cylinder machines... one way to give it a "quick check" is when you load up the cylinder machine with a pair of CR39 lens run it for about 15 seconds and than pull them back off and see how the lens looks.. within that 15 seconds you should have gotten a nearly uniform smoothing out of generator marks..they will be light but you should be able to see if it is smoothing it out across the lens as it should.
The poly and trivex (poly more so) is the harder stuff to do, CR39 is the "easy stuff" :) ....
1) check your pads ..the pads you are running are probably to agressive for cr39.. cr 39 should be around a 600 grit.
2) check your run time and air pressure on the cylinder machine
You think it might be because you are making a foam tool and re-running it, I would tend to think it is just because you are re-running it that the swirls are being removed.

Swirls usually are in a lens because, one the run time and air pressure is incorrect. Two, the wrong pads are used. Three polish is broken down, but that is more a "frosting" type look than major orange peel.

Are you using a one step system or two in your cylinder machines? I would start there and take a good look at the pad grit.

Here is what I run. First fine 600 grit at 1:10 18 pds. pressure. 2 nd fine 9 mic. blue for 1:10 18 pds. pressure. 3:45 for polish and it is polish FOR cr39/high index..

You can elimanate your generator or you would have power problems across the board, you can eliminate the cylinder machine being short stroked or off axis or all your stuff would be coming out incorrect or hit and miss.. I would take a good look at the grit of the pads and the polish if it were me.. :)


Jeff "gee usually it's the spectralite giving people fits" Trail

[APV Optical]

Thanks for all the replies. For cr-39 I am using p-1200 honeyfine brown one step pads. The polish is for hard resin, high index and poly. My fining for cr-39 is 2:45 secs with 18 psi then 4:00 polish. I have some older pads we use to use. One step they are red ptr-767?? Anyway I will try those today....(fingers crossed) Thanks again...

[JRS]

There are much better 1-step pads available than a 1200 Brown. The 1200 brown was a 2nd fine poly pad - if memory serves.

Try the yellow and orange striped pads - from PSI, DAC, etc.

[Jerry Thornhill]

I had this problem many years ago when I first started doing CR.
Since you mentioned when you change the lap the problem disappears I will share what it was in my situation.

Look for dings on the edge of the lap. It is amazing how many dings occur on the edge of the tool. This little ding created a raised spot on the edge of the lap. When the lens went over this spot I got swirls. I found that this was what was causing the problem. No more swirls for the last 15 years.

Jerry

[harry a saake]

polishing

back years ago when i was in the labs with B&L, we had an automatic cribber made by coburn. After the lense came out of the generator, they would be cribbed down as needed, and then be put on the fining and polishing machines.
.....While i have also seen that same problem happen that jerry alluded to, cribbing the lenses down seemed to work pretty good and i wonder if its used today.

[Jeff Trail]

Jerry,

Since Chris had no problem running the poly's and the Tr-vex with these tools than I would think it is not the "tools" but in the process with the pads or polish :)

Harry,

Instead of crimping I always prefer to just set the stroke on the cylinder machine, a lot of people have no idea that this can actually be done.. it saves the cylinder machine wear and tear and makes the job come out better, I have one set up for short cycle strokes 70 mm and smaller and one set up for the largest stroke cycle I run all my over size and PAL's on..

One other thing that could be causing the problem is that the cylinder machine is slightly out of calibration, the more agressive grit pads for poly and tri-vex are eating it up where you would not notice but in a cr39 where you have a different run time and pin pressure this could be a big problem.. I would double check and make sure that the heads are lined up and on center with a set of cyl. blocks.
I'm still leaning towards the pads or polish or a combination of both as being the culprit.
Gee it is usually the other way around poly's and tri-vex being the pain not cr39 :)

Jeff "boy it can be frustrating when it does not come out" Trail

[Susan Henault]

I have a few questions for the lab experts, just for my own knowledge. Does the application of a backside hard coat reduce (or render invisible) the appearance of minor surface imperfections? Also, do labs generally inspect the surface quality before or after (or both) the scratch coat application (for the lens materials that require it). I know that I am risking coming off like a dumb bunny, but I really want to know. Is it possible for a larger scale swirl problem to go unnoticed, because things slip by after the application of backside hard coating?

Please ... go easy on me ... ;)

[JRS]

Susan, (hello btw) putting a backside coating on scratched lenses usually hides little. Extremely light marks - sometimes.

The bigger problem can come later if the lenses are AR'ed. Minor, or almost non-visable (to the eye) marks will show up when the AR is applied. Depressions, grooves, pits, raised spots, etc. all tend to rear up and become visible after the AR process. It is usually a waste of materials/labor to hide issues under a backside coating used to mask the real problem.

Now, that said - there are techniques in use for using a backside coating instead of polishing. The normal process for this does not use the typical fining process. Some methods use very smooth cutting from a generator (or similar device), others use a series of fining pads. Polishing (and sometimes fining) are skipped, and the lenses are coated. These processes have some limitations in either materials and/or rear curves.

If you are interested in seeing some of this "stuff" - call me when we're at VE-W and I'll walk around with you. If you don't mind, that is.

[Jerry Thornhill]

Jeff
The reason I brought up the tools having burrs and eliminated the other problems was that he stated when he changed to a foam lap the problem went away. That would seem to eliminate pads and polish.

Harry, I happen to now have the ability to crib on the generator and I crib and pin bevel everything. It makes everything easier. slows down the generating a little but regain the time in the finish department by not having to edge as much off. It also cuts down on twists.

Everyone has their own little system that they use. If my curves are not toatally fined in in 15 seconds my generator curve isn't as good as it should be.

My first fine and my second fine is at 1.30. My polish is at 4 minutes. I have my pressure at the finer at 14 pounds. My pressure at the polisher is 12 pounds. I run all materials but Trivex and Poly this way. There is never a problem.

I increase the pressure to 18 pounds for Trivex and Poly. The first fine is 1.30 and the second is 2 minutes. I polish these for 6 minutes.

I also prefer an 8 leaf pad. My second fine is a 3 micron. Since I run 50 per cent a hi-index of some type I find that the 3 Micron pad works best for me.

As far strokes I have one stroke setting and that is where it stays except on an extremely high minus that causes trouble which is rare. Maybe once every couple of months.

Like I said everybody does it a little different and what works great for one may not work may not work great for the next.

Jerry

[JRS]

Jerry, your times and pressures are very good. Most people want to INCREASE pressure, but you know better.

The summary on 'burrs' is also very valid. It could well be something as simple as badly managed tools (laps). We do have a tendency to over dramatize these situations.

PS - I think you could probably not increase pressure on Trivex and Poly, and still do quality.

[Shutterbug]

We notice a similar problem when our gripper pads are wearing at the edges. For some reason, the CR39 is the first material that is effected. New pads eliminate the problem. If you are using gripper pads, you could look at that as a possible cause.

shutterbug