Help Power Issues and Umwanted Prism

[olmeca]

Hi I wonder if anyone can help me.I have a serious problem. I own a mini lab and we are experiencing problems regarding power issues and prism.The power issues are either .025 to strong or to weak or a unwanted cyl of 0.25.Its very erratic and does not happen with every job.Also now and then we struggle with prism for example one eye would be 1.5 base down and the other 0.5 base down which is also very erratic

My breakage is up to 12%.We are using an Alloy blocker which is set at 130 otherwise the alloy blocks the nossel where the alloy is dispersed out.Most of the problems are appearing on progressives lenses. We do a lot transitions and 1.54 coloumatic.We normally wait 30 minutes before we generate the lenses , so the alloy can cool properly.I been thinking that its either operator error or the heat of the alloy. Please any assistance would be appreciated.

Regards

Olmeca

[Aarlan]

power and unwanted cyl:
-what temp are you cooling your water for fining down to? same quest for polish. Are you using metal tools/laps or cutting your own?

prism on progressives is 99.999 percent likely operator error. not holding top firmly down when blocking, overfilling, debris on block from last use, etc. Is the same person blocking all day, or do you have diff people? only other two issues for prism would be improper generator settings, or debris in the chuck during edging. a small amount of prism may be accounted for with improperly maintained cyl machines, but not 1.5 prism diopters worth.

AA

[olmeca]

Hi thanks for the reply

Fining direct water supply
Polish is cooled to 5 degrees Celsius
We are using metal laps.

Regards

Olmeca

[olmeca]

I was using one person but now moved him off and put someone else on just to see if it is operator

Any suggestion on the powers.

Regards

Olmeca

[Aarlan]

One of the problems w/ direct water is the lack of control of temp. A recirc unit will allow exact control (just like your polish). In the summer, there is a possibility of warmer H2O temps running through your finers, resulting in possible warping, power and cyl issues....I've found this happens a bit more w/ Wax blocking, and less so w/ Alloy, but still may be something to look into.

What kind of maintenance is being performed on Cyl machines?

Also, what materials materials or designs are coming up with the most problems? If you are getting more on specific materials, the fining times or pressures may need to be adjusted, or some tweaking may need to be done re: curve calibration. If it is one specific design (plastic ST28 in a 6 base for example) the Sag value you have in the computer may be incorrect, and need to be updated.

Also, have you changed the type of fining pads you use or base pads you are using recently on the metal laps?

Most importantly, look for patterns. Make a list of every job that is off, in which direction it is off (too much plus, too much minus), if there is unwanted cyl. Record the material, BC & Add, manufacturer, whether it is R or L eye or Both, which machines you are runnning the jobs on and look for distinct patterns...that will help you narrow down the cause (or causes). It is more work, but will save time and money in the end by finding the root cause and eliminating it

AA

[scriptfiller]

Direct water in a no-no in the south. The water coming into our building can be in the high 80's - low 90's. Our pipes run right under the parking lot in the front of the building.

Double check the seating of the lense on the block. If the lense is not properly seated on the block, be it by even 1mm, can induce the reported variances. Make sure you are holding the distance section of a PAL when blocking. I generally place my thumb on the distance RX check circle then apply pressure outward to the top of the lense.

[cmhargrove]

With varying degrees of prism and power, i would sure suspect your blocker.

You might try to reduce the flow volume/pressure of your alloy. Sometimes when the alloy flows too rapidly, it can push the lens and induce prism.

Also make sure if there is an elevator shaft on your blocker that it is operating freely. Sometimes, they can bind and cause these issues. Another way to check this is to have your operator to "tap down" on the block to make sure it is properly seated before placing the lens on the block.

Have you also had thickness problems? Too thin or thick?

[olmeca]

Hi Aarlan

Thanks for your reply. I know we have been changing pads because our current supplier was out of stock of the pads we were using before.

I will take your advice and check for patterns.

Thanks once again

Regards

Olmeca

[Aarlan]

. I know we have been changing pads because our current supplier was out of stock of the pads we were using before.

This is an often overlooked problem. If you start using base pads to protect your laps, or if you change the fining pad design, you may have to adjust the pad thickness compensation in your surfacing program. If the pads are different thicknesses it will change the tool that your surfacing program chooses. A thick pad coupled with a base pad will add enough thickness to change the effective radius of curvature of the tool being used. there is normally a way to change that in the program itself. Make sure to use the same company's pads rather than switching back and forth. If you change manufacturers, measure, change the comp value in your program, and then be sure to REcorrect the value when you switch back.

This is getting very nit picky, but can make the difference between some jobs being within tolerance vs being just outside of tolerance.


AA

[Bob MacNeil]

Two things, if it's 117 alloy, it would be most helpful to operate below 122 f , when you can make a good low powered sphere, your off axis problem will normally clear up. The most stable blocking process for progressive lenses is the use of a three point blocking ring, it can give you some legacy issues for a few years with customer redos , but the TRP is very constant by add power.

Bob

[Georg Mayer]

Generally I still suspect the blocker as the main culprit.
Check seating, check all your inserts on the seating surfaces, if they are thrown around and have nicks, burrs and dents where they seat they induce unwanted prism.
Polish at 5 deg C sounds low to me, but that might be related to your set-up, machines and consumables, especially if you don't have these problem on all lenses, you menitoned mostly Progressives? That to me is the crucial point to establish.
If that is really the case then you must follow scriptfiller's point, to press down for good seating in the distance portion of the lens during blocking.

Georg Mayer
Rodenstock Munich

[MikeHolbrook]

Hey olmeca,
I don't have much experience with alloy blockers, only wax. Its just a thought, but do you think 30 minutes is too long of a cooling time? It takes my wax about 5 minutes to cool but If I leave it blocked overnihgt, I notice problems. Like stated above, if you have any nicks on the nipple or stem that could cause chaos. Just a quick rub with a fining pad should fix it. Also with the power issues, have you thought about checking the calibration on your lensometers? I know it seems strange but oddly enough I have seen this fix many power issues. Not every lens gets generated and fined exactly the same so some lenses could read strong while others are reading weak and the lensometer could just be the culprit. That would be my next step if you think the blocker is ok, and the cyls are calibrated. I like to check the easy things first then move to the more complicated. Good luck. -Mike