Jeff: Surfacing Ormex???

[Jo]

Jeff:

I need your help. Have you ever had any problems surfacing Ormex. The brand lenses we are using are called Views; we are running them with an alloy blocker with chiller rings, letting them sit in ice water after blocking and cutting them on an SGX. Almost all of our minus lenses are coming off surface wavy and .25D off power. The job tickets appear correct. Any ideas???

[Jeff Trail]

Originally posted by Jo:
Jeff:

I need your help. Have you ever had any problems surfacing Ormex. The brand lenses we are using are called Views; we are running them with an alloy blocker with chiller rings, letting them sit in ice water after blocking and cutting them on an SGX. Almost all of our minus lenses are coming off surface wavy and .25D off power. The job tickets appear correct. Any ideas???

See those words..."strong" and "wavy".
That is the sign of one of two things...heat, or incorrect surfacing :).. now I hate to start at the basics..BUT you are cutting all those Ormex's on center.. no prism for decentration right? .. if you are using prism then they never will come out right, ormex is an aspherical design. The check out on an aspherical lens when the OC and the geometric center off whack.."axis problem..appears as a wave" and " power problems" power along an oblique axis. if you check the lens slightly off center..say move it over a half^ or so does the wave go away and the power come in?
The other place where I see the problems are in removal.. almost all the high index (and mid index) you need to cut down the amount of removal o a sweep.. especially in a minus because it will "warp" the lens (and no the old trick of setting in hot water will NOT take it out).. the next place I usually see a problem is on the cylinder machines.. check and make sure you are running it at the correct pressure and run time.. to long and this lens is very sensitive to heat from friction.
Oh and if you are not cribbing the lens, then having a dremal drill or hand stone to take off some of the "sharp" edge will help in the finishing..
Other then those, well I can't really tell.. I know I pop them out without any problem.. what ever you are doing though is very popular I get your question a lot for some reason.. minus always strong and waves.. usually people were not cutting them on center or the problem was in the blocker or cylinder machine..
You are running 117alloy right? ..maybe want to double check your temp's..these lens and sunsensors and quantum's seem to be very sensitive to surface heat, more so then others.
You do know one of the guys that is in the opti-board gang is a "trouble shooter" for Essilor (JRS).. I'm sure he would have a ton of stuff he could fax you where you might compare your run to what the factory recommends.. and then give him a call and compare notes.. hey seems like a "cherry" job to me!! :rolleyes: ....JR???..want to fill in any places I missed and help a fellow lab rat out?

Jeff"I can run them but explaining it sometimes I miss the points" Trail

[HenryB]

HEAT BAD!!!!!!

Start at the beginning.....
1. Check your alloy temp (I doubt this is your problem though)Also don't dump it straight from the reclaim tank into the blocker tank....the reclaim water is hotter and the alloy should cool down a bit before being put back in the blocker. Oh and I dunno if that ice water thing is a good idea.....doubt it is directly affecting this particular issue but that much shock to a warm lens can't be good. Do you have any deblocking problems???? What I would suggest is a minimum of 30 (45 is even better) minutes of cooling before generating at room temperature.
2. Check your curves on your generator...THIS IS SUPER important....if they are off you are wasting your time with eveything else for the most part, and this typically causes the most problems on high minus lenses cuz of the thin centers....The curves off the generator should be .03-.04 flat so that lenses fine from the edge to center therefore reducing friction (heat) on the center of the lens. Whne you get the curves set, run a lens or two for 10 seconds and dry it off and check the surface.....it should be pretty much fined out except for a small portion of the center (maybe as big as a dime or so not fined out)
3. Like Jeff said, cyl machines times and pressures are important too....specifically don't run these soft materials longer than the manufacturer says....also, make CERTAIN that you are getting good polish flow on your lenses when they are polishing or else.....WAVES!!!
4. Check temps on your fining water and your polish also....anything over...uhhh....low 70's you should keep a close eye on it. It may start causing problems.

If none of this helps I would certainly give Essilor a call, those guys are good and can help you out alot. In fact, most of the things I have mentioned here are exactly what they will tell you probably....


Good luck......

[JRS]

Jeff and Henry have most of down Jo. However, Henry did state generate FLAT by 0.03~0.04 but stated the result correctly - fine from edge to center. Which means the lenses will generate slightly steep.
Never, place an alloy blocked lens in cold water to speed up cool down. This only helps warp the front. And he is also correct on placing alloy - straight from the reclaim tank back into the blocker. Don't do it.
Using the SGX (dry cut generator) requires that the air nozzles be positioned so that they assist in keeping the lens cool when generating. It is also important that stock removal (per pass cut) be less than you would use for CR-39.
Lastly, and one point that is commonly overlooked is beveling prior to fining/polishing. This is an important step. Think of the sharp lens edge as a squeegee. It will press the fluids out from under the lens. A beveled, and I mean well beveled, lens acts like a snow ski tip - the fluids are forced under the lens. Thus allowing better fining/polishing action, and cooling (never seen anyone use a Dremel tool for beveling, but to each their own). While on the subject o cooling - both fining and polishing fluids should be between 68 and 65 degrees F.
Hope this is helpful. And as Henry suggests... call Essilor Tech Support for a visit to your lab. They will be happy to assist you. Actually you can call me (if being the one responding helps) @ 1.800.377.4567 x5834. Just leave your phone number and I'll call you back. At that time I can also have a book titled "Laboratory Procedures Manual" shipped to your location. Contains tested recipes for all materials, and the tinting section I had posted here on OptiBoard.

J.R. Smith

[This message has been edited by JRS (edited 09-28-2000).]

[HenryB]

Oops.....yea what JRS said......I meant steep. DOH!!

[Jeff Trail]

JR,

Really, you never seen a dremal by a cylinder machine?..I didn't think my way of doing things were so "odd"...I have a "V" shaped attachment on my dremal..acts like a little "grinder".. it's great fo just taking the thin sharp edges off on high plusses so they will not catch on the pads when finishing them out..beats having a hand stone there and it's easier to work with, I have the flexible shaft attached to the dremal and it takes two seconds to take off those edges..I have a larger grinder over near it to take off the corner edge on higher minus lens & high cylinder.. the problem a wholesaler is going to run into is we do a lot of uncut work, so no way we are going to be able to crib a lens :-)
I have had a couple people tell me that dremal thing was weird, but then again I NEVER have a lens crack or chip on me when I'm running it through the first or second fine because the thin edge catches a pad :)
Ever see the temper tandrum thrown when you were cutting that +5 high index transitions and on that second fine that knife edge catches the blue pad and "chip" off breaks a pc. and it won't cut out!! :rolleyes: .. well by taking that sharp edge off slightly with my dremal..never happens to me :)

Jeff"hey sometimes my crazy idea's do save money" Trail

[Just Me]

Just a suggestion:
If you find that the water to your finer is running warm you may want to consider buying a water cooler from w.w. grainger. Makes a world of difference and only runs about $500.00.

[so]

We don't normally have problems with ormex, but we used to have terrible trouble with spectralite. Putting the lenses in cool water didn't help. We now allow them to cool naturally. We also changed fining pressure to 14 lbs. 1 minute 1st fine, 1 minute 2nd fine, 4 minutes polish on a thicker pad than before. Our fining water is very chilly, and polish is 65 degrees. It has made a world of difference.

[Blake]

When this thread first started, I glossed over it, but now that we're stocking Ormex lenses, I decided to take a closer look.
We haven't been having problems with them, but I do wonder why RxCalc calls for such flat lenses. For example, a +2.50 Rx would call for a 5 base lens. I know the index of refraction is higher than CR-39, but I still think that's too flat (besides, it makes surfacing a pain in the backside).

Blake

[JRS]

Blake, the only reasons I can think of, for RxCalc to use a 5 base on a +2.50 is;
1) either the base curve chart within the system is set wrong, or
2) the system thinks they are 'aspheric' lens types.
Check your documentation on how the base curves are selected across power ranges. On most systems this is user defined - unless supplied by the originating manufacturer.


For SO - it sounds like you are processing mid-index the way it should be done. Lessening the pressure reduces heat. chilling the fluids reduces heat. And heat is the enemy. Some final thoughts (that maybe redundant to the thread but I'll gamble and repeat);
1) NEVER rapid cool lenses my placing in ice water.
2) Avoid letting the fluids exceed 68 degrees, nor drop below 65 degrees.
3) The difference in tempurature - between the fining fluids and the polishing fluids should vary by more than 5 degrees.
4) NEVER put alloy, straight from your reclaim tank, directly in the blocker.
5) PSI should not be greater than 16 lbs - at the head (pin type machines). Never trust the dial on the machine - measure it. On LOH machines, the pressure should not exceed 0.3 bar, nor drop below 0.25 bar (without other adjustments to the machine).



[This message has been edited by JRS (edited 02-28-2001).]

[shanbaum]

Originally posted by Blake:
We haven't been having problems with them, but I do wonder why RxCalc calls for such flat lenses. For example, a +2.50 Rx would call for a 5 base lens. I know the index of refraction is higher than CR-39, but I still think that's too flat (besides, it makes surfacing a pain in the backside).

Blake

So, your backside would feel better if you were having problems with them?

Your RxCalc is probably selecting base curves the way it does because a chart is assigned to the Ormex Lens Type that tells it to pick a 5 base up to a +4.25 sphere - which I suspect is what Essilor specifies. I'm not certain, because I don't have the Essilor documents handy; but that's what our current chart contains. If that's not correct, let me know.

The lens is aspheric, by the way; flatter front curves are typical of most aspheric design specifications.

[Jo]

shanbaum:

JRS is Essilor Tech support; see his post above regarding the documentation.

Our lens library was not always up to date; many times the lenses have come into stock before they were in the library. Our generator is set up for speed as upposed to maximum accuracy. In the case of poly for example, the "#"fluted blade we were using and the generator cutter settings were set up for speed which slowed life down in the long run because every other job you had to clean the melted poly off the blade.

[HenryB]

Jo....THAT is your problem.....if the speed settings and cutter you are using are causing poly to melt....WOW...you need to change that immediately. As the above posts state, heat in processing is your #1 enemy and often times a little heat will wave lenses just enough to make you think you have a power problem....when in fact you don't, you have a wave problem.

I would suggest you contact Gerber to verify with them the proper generator removal, speed, etc. for each material for your particular set up.

Oh....I believe Robert is right, they are aspheric.

[shanbaum]

Originally posted by Jo:
JRS is Essilor Tech support; see his post above regarding the documentation.


I know JR, I know where he works, and I'm sure he can look up Essilor's base curve recommendations for this lens faster (and more authoritatively) than I can. As I think I wrote, if a +2.50 Ormex is not supposed to be ground on a 5 base, I'd really like to know about it. We are perfectly capable of misreading manufacturer's specs.

[Jeff Trail]

Gee you guys are touchy.. :) .. all it amounts to is the program is using the basic formula for optimum base curve selection and when you go from spherical to aspherical it will automatically knock off 2^ of curve when recommending base curve..

From Jo's come back of "we are looking for speed in production" I would say the culprit is and always will be in that situation HEAT.

One way to slightly increase the run speeds are to go from alloy to wax for blocking (if you are having heat induced problems in blocking) OR another option is to make sure you keep your blocks refrigerated, which is what I do...
The biggest mistake I see is usually the blocker is run to hot, once you warped that lens with alloy to hot the rest of the trip (surfacing) is wasted.. one easy way (besides checking the alloy temp) is to hold the lens up and if you see a "warp" the same size as the block you used..weeeellll.. :rolleyes: You guys wouldn't believe the times I have been called in to "help" correct surfacing problems and I'll find that little problem real quick..

Jeff "gee guys don't take things so personally" Trail

[shanbaum]

Originally posted by Jeff Trail:
Gee you guys are touchy.. :) .. all it amounts to is the program is using the basic formula for optimum base curve selection and when you go from spherical to aspherical it will automatically knock off 2^ of curve when recommending base curve..

Touchy? TOUCHY? OK, Mr. Florida Smart-Guy, you come up here and shovel snow for two hours, and we'll see who's TOUCHY. Why, I oughta...

BTW, we prefer to allow lens designers to specify the base curves on which they want to see ranges of powers ground, as opposed to using some rule-of-thumb.

[so]

Shanbaum,
Back side is fine, thanks for asking. Do occasionally have a few problems. Thought this website was about sharing...sorry to disturb you.

[JRS]

I want to clarify my initial response regarding the base curve selection on Ormex.

I did not imply that the selection was wrong, only the places that the base is chosen by a system. The following list is the recommended (Essilor) base curve to power range for ASPHERIC Sv Ormex. This is a direct quote from our (Essilor) manual.

BC 1.00 -12.00 to-8.25
BC 1.75 -8.00 to-4.25
BC 2.50 -4.00 to-0.75
BC 3.50 -0.50 to+2.00
BC 5.00 +2.25 to+4.00
BC 6.00 +4.25 to+5.25
BC 7.00 +5.50 to+6.50
BC 8.50 +6.75 to+8.00

I hope this clarifies the issue. And, as you will note, a +4.50 does not fall on a 5.00 base. Again, I suggest that the system may influence (decrease) the base due to the cylinder - which was not stated in the original message.

J.R. Smith
Essilor Technical Support Mgr.

PS - I certainly agree with Robert - the best lenses are produced using the suggested curves from the manufacturer. Most lens manufacturers spend a great deal of effort working those out - we don't make these up.

[This message has been edited by JRS (edited 03-06-2001).]

[This message has been edited by JRS (edited 03-06-2001).]

[Jo]

shanbaum:

Ditto on the snow. Dug out this morning got in and dry then the snow kicked in again early this evening. I am tossing a coin in regards to going out again now or tomorrow. I am 99.9% sure tomorrow is gonna win even if I have to cheat on the coin toss. They say we're in for another Noreaster on Friday. Don't the weather guys know its March; enough's enough.

Sorry if I came across wrong; I just wanted to point out to folks JRS offered the Essilor contact # for the documentation if they needed it. I was also hinting to Blake that the places we work(ed) at don't necessarily follow either lens manufacturer's or Gerber's recommendations all the time. The didn't follow Coburn's recommendations either in the beginning. You are left to grin and bear it or of course bang you head against a wall, but that hurts.

[shanbaum]

Thank you, J.R., it looks like some of the breakpoints in our chart are 0.25 off - but the +2.50 sphere does indeed belong on a 5.00 base.

[JRS]

Yes sir, it does. Flatter bases on aspherics is exactly what we want. And the rear sphere should be in the high -2's or low -3's when you surface it.