hey all-
ive recently been put in charge of a gerber lab. The generator the lab has is a Gerber sgx. I'm running into a few issues I cannot troubleshoot. With progressives, techs keep getting unwanted prism after the lenses are generated. I was wondering if there's a way to troubleshoot this. When marking/blocking, everything is on the money. Is there something I should do on the screen that will prevent this issue? Thanks for the help.
Only progressives?Originally Posted by slackware
I would suspect they are blocking them wrong.
Is it unwanted prism or prism thinning?
I need a little more info. Give me a call.
Just unwanted prism. I'll have the o.d. at 1 prism diopter bd and one dead center in the center reticle. I'd reblock the o.d. since it has the most bd prism and toss it back in the generator. Sometimes it works but other times it doesn't. I was going to up the temperature on my chiller to see if that would help since it's ice cold constantly and wax hardens in the spout.
As an example:
today i had od: +1.25 -.50@90 os: +1.75
i had the od prism at .50 bd and the os at 1.5 bd. i figured id reblock and see if i could generate the prism out but nothing.
hmmmm.....
Being that it is "only" progressives I highly doubt its the generator. How do the flat tops look? Is it a random problem? Or is it every progressive?
it's pretty random like 2 out of 20 jobs. i was thinking maybe it's the basecurve of the blank or is there a setting i can use? i usually add 3mm to the blank diameter and 3mm to the edge thickness and clear the cribbing and leave everything else. any suggestions?
if you have a step one or eclipse blocker, then take the elevator plate off by the 4 screws, underneath that will be a spring and a washer which is screwed down. check to make sure that screw holding the washer down is tight, and make sure that compartment is free of excess wax, then reassemble and see if that improves it. if you want I will call you and try and help you that way, I had the same problem many times. Just pm your number, or Ill send you mine
OK, Since it is random it could be a few different things.
Again, feel free to call me.
Make sure your blocks are in good condition. You might have one damaged block which is not getting chucked properly. Also check your chuck itself. Make sure the tooth is tight and you cannot physically pull or move the blocked lens in the chuck. Its possible that your block is getting partially pulled out causing the prism. And as Hyperoptic said, make sure your elevator plate is not being randomly obstructed by debris. That is critical and could cause random prism. Also the rubber on the elevator should be in excellent condition.
I am sure you will find the problem with our help here. I believe it is a physical problem and not in the settings.
This may be a crazy shot, but make sure the cribbing on the SGX is set from back to front, ours came default from front to back and the tool used to yank the lens and block out of the chuck juts far enough to cause some prism, everynow and again it even yanked the lens from the wax.
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Its not that crazy:hammer:
I had an old habit of pressing toward the chuck when I was deblocking the lens. If you press the lens inward while pressing the chuck button, you will know whenever a block slipped because it will move back into place.
You could head off a lot of breakage before its discovered with that little habit.
Since it is doubtful that the SGX has the ability to sniff out progressives as opposed to other lens styles, it is almost certainly a problem in blocking.
RT
Thats what I said in the beginning but the OP never confirmed that its only progressives. It is very possible that the progressives are being blocked incorrectly.
You should also verify the prism diopter and prism method settings.
RT
Judging by the erratic nature of the unwanted prism problem, then it's probably caused by lab tech error.
If the block you're using is the 95W or the OWC blocker.
When the cylinder axis is close to 90 degrees it can be somewhat confusing to a less experienced lab tech in what location to hold down the lens when blocking a lens.
Check the temp on your wax. If it's too hot it may not be solid enough when you remove it from the blocker and creating prism by tilting the lens in relation to the block.
My advise would be to watch over your tech and see how they are blocking the progressive lenses. Assuming this problem is only in PALs.
vlad-
i increased the temperature on the chiller since the wax blocker, well since ive been there has always cooled the wax in the spout. hopefully it'll correct the issue. since the sgx is fairly new after being away from it for 4yrs, when i put the new measurements in, i usually add 2mm to blank diameter and edge thickness per a LM told me. and the last option, the crib i clear out. works great for s.v. generating and bifocals, but any trick for progressives or something that's a chinese secret out there? i observed 2 techs today to see and i couldnt see anything wrong. also, on the lab software we both know, the job would call for a red block while on the generator it would show blue. is it a glitch or do i just asterick it over to blue from red? been doing that lately. seems all questions i ask to other people that have been with gerber for years wont say anything. knowing me, ive always been with the old school coburn manual generators haha.
Don't worry about the difference in block selection - Gerber blocks all have the same critical dimensions (unless you're instructed to use the auxilliary ring - that does matter). When the software and machines show a different block, you're in a boundary region where either is acceptable. The only difference will be the thickness of the wax "cookie".
Most progressive lenses tilt in the blocking ring, producing unspecified base down prism, nominally around 0.25D-0.38D. Most labs I'm familiar with ignore this, because it's innocuous. Some designs produce a lot more (as much as 1.5D) - which requires some work to eliminate.
I don't know anything about the Gerber system, but does the ring have a rotateable cutout section for you to place large flattop segs in to keep the lens evenly flat on the ring? If so make sure your tech keeps the 180m line of the prog running across two places where the cutout is not and holding the lens on the ring with two fingers above the 180 line. Otherwise if one side of the 180 line is placed where the cutout is, you will not have the lens set evenly flat on the ring and will experience lateral or diagonal prism.
That's how it works on my solid alloy system anyway.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
Yes, there's a cut-out section at the top of the alignment and blocking rings to allow for a seg to be placed there, and it's certainly possible to induce prism by allowing a progressive lens to tilt towards it. Because of the profile of a progressive surface, it would be possible to do that even if the cutout weren't there.
The cutout on the Step One and Eclipse blockers is invariably at the top; lenses (with the exception of round segs) are aligned in a normal rotational orientation (that is, rotated as they would be in a frame), and the block is rotated to the cylinder axis - unlike the old methodology you're using.
But even if one does correctly seat the top portion of a progressive lens against the ring, most progressives will be tilted, inducing some (usually small) amount of base down prism, as I wrote earlier.
Maybe it was just our Step One, but I always had to manually press on the top of the lens on progressives to make sure it seated flat. Sometimes it would move and sometimes not. Every time I felt the lens move (Seat) I knew I had saved it from unwanted prism (ALWAYS base down). It was inconsistant.
Yes, you have to press on the distance portion, and no, it wasn't "just your Step One:. Some lenses will rock slightly even when you do that, and you can't really know whether you're rocking prism into or out of the alignment. Of course, if it "seats", that's where you want to be. Some of them simply don't seat (one example being the AO Omni without the stick-on tab - that's why they had the tab).
Fiber rings on the old system had the same problem - only it was more difficult to control.
If you really study the profile of the top lip of the Gerber Step One blocker, you'll notice that it is not solid. As Shanbaum mentioned, it has the required seg cutout. But it also has cutouts that ensure that the lens only touches the ring at approximately the 90 and 180 degree areas. That design reduces the unwanted base down prism in progressive lenses from a typical 0.25 to 0.50 to approximately 0.12 to 0.25 diopters. That's a huge advantage over conventional blockers.
Because there are no spherical areas on the front surface of a progressive, it is impossible to align the progressive in a perfect position on any blocker. Step One minimizes the error. Lens designers invariably say "As long as there is no imbalance, who cares?".
Some Lab Management Systems are able to predict the amount of unwanted base down prism due to front surface geometry, and compensate it in the instructions sent to the SGX. If you are experiencing more base down prism than the workticket calls for, it may be that your system doesn't compensate for it. Or as Shanbaum notes, you may not be pressing in the distance portion when blocking. That's been standard practice forever regardless of which system you block with.
Why aren't you cribbing lenses? Cribbing invariably gives you bettter results in fining and polishing, and reduces the chance of fined in prism. Cribbing is a no-brainer--always do it.
RT
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As an LM I used to always crib. It helps keep the lens cooler since there is better water/polish slurry flow into the center of the lens.
But the problem is that with one hour service, it's not a very popular thing to do.... for obvious reasons. But I used to do it anyway.
Is the prism that you see at the distance circle or at the fitting cross? Are you sure you're not prism thinning?
Perhaps these have been answered and I just missed them.
Is it the same person blocking all jobs? If not can you pinpoint it to one or two people?
We have an occasional issue that appears when a specific tech works. Usually it's because he's rushing and chucks the lens into the generator not flush.
And I agree with always using the crib feature. Especially with progressives. Those paper thin edges on plusses can easily crack and chip causing cut out issues at edging
r u doing the calibration disk correctly.if so,try calibrating the sgx for prism, if not found there it has to be in the step one. trust me those r the only places were it could happen.
If the problem was not resolved by now, they have shut down the lab. I would like to hear what the resolution was.
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