Axis Problem

[CKPolar]

We are having a very strange occurence. No axis problems and then boom, every once in a while a ft will be off axis by about 7 degrees. If it was happening on everything I could see a problem, but it is spread out and low powers for instance +100 -75 55 was our last rx this happened on. Any suggestions, could the laps be bad or maybe the lap isnt seated correctly? Confused Thanks

[shanbaum]

Tell us what equipment you're using - especially for surface blocking and generating.

[CKPolar]

Step one wax blocker, sgx generator, laps are .12 and Acuity and 5004 finers

[shanbaum]

OK, can you tell me a little more about the frequency of this? Does it happen on the order of once every 10 lenses, or every 100 lenses, or what?

[CKPolar]

We Have Not Noticed Any Kind Of Sequence

[shanbaum]

Well, you said "every once in a while"... I suggest calling GC field service and asking them to help you in making sure that your Step One isn't acting up. From what you've told me, that's where I'd focus. The elevator plate rotates the block to the cylinder axis; perhaps it is occasionally malfunctioning. Might need cleaning or something.

[RT]

It only happens on flat tops??? The Step One elevator mechanism has a sensor that detects lined bifocals and only malfunctions on those???


Shanbaum has made the assumption that you're talking about axis errors detected during Surface Final Inspection. However, the original question leaves open the possibility that you've edged the job off axis and have actually surfaced it correctly. A little more detail...

[shanbaum]

It only happens on flat tops??? The Step One elevator mechanism has a sensor that detects lined bifocals and only malfunctions on those???


Shanbaum has made the assumption that you're talking about axis errors detected during Surface Final Inspection. However, the original question leaves open the possibility that you've edged the job off axis and have actually surfaced it correctly. A little more detail...

You're right, I was assuming that it was the surface that was off axis, and not the segment. Good point.

[shanbaum]

...which brings us to the question I should have asked in the first place - which is it, the seg, or the surface?

[Shutterbug]

The other thing about the step one is if it is not sweating enough, it won't eject the lens correctly and can error out when resetting. I would also suspect the blocker first, but it could also be one finer or polisher in a series. Try numbering the machines, and putting that number on the work tickets for awhile to see it the problem follows one machine or is random.

shutterbug

[CKPolar]

Great Il will give it a try, It is happening in the surface final inspection, not edging. It is usually on lower powered lenses and the axis isnt off dramatically, just enough to reject. Im thinking more along the lines of the finer on our older coburn 5004. Thanks again for te replies.

[Jubilee]

Depending on what type of generator you use, it could be a sign that the blade is dull. I know that the having axis issues with low cylinders seem to be the first sign I see. It is amazing as soon as I change a blade how things start to clear up. And yes sometimes I have to change a blade as early as 300 cuts, but sometimes can get 850 or more before having issues.

I think the reason why it is also more noticable in flat tops is due to the ledge on the flat tops. The power will sometimes bleed into the lensometer when the OC is within a few mm of the seg.


Cassandra

[mrba]

If the problem is not occuring in any predictable fashion, it could also be the blocker operator...

[RxSam]

i hope by this time you've got got the problem solved, but if not, your round seg could be off also and your not seeing it as easy. The trouble could be in the finer pins or worn center on your blocks. If the lens are not polishing out OK the trouble is in your finers. If the lens are polishing out OK the trouble is more than likely in your blocks. If the trouble was in your generator your lenes would not fine in correct.

[slackware]

correcting off axis

either be progressive or bifocal, the one trick i use to correct it is:

if let's say the right eye is off by 7 degrees more and the actual prescription is 17, therefore you are reading 24, subtract 7 from 17 and mark the lens at 10 then refine the lens. usually it will bring the axis to the prescribed axis. make sure you use the same lap tool when refining. refine for about 1 minute with 20psi for poly, 30 seconds for plastic. second fine poly: 1.5min, 1 minute for plastic. polish poly for 6mins at 20psi, polish plastic for 4mins at 20psi. if you run into this, give me some feedback to see how you did with this.

remember, if it's over the prescribed axis, subtract from the prescribed axis by how many degrees off.
if it's under , add to prescribed axis.


sidenote-
you may want to recalibrate your finer with the cylinder blocks. i recalibrate them before each day and after each day, and once again in the morning and at night everyday. it can be also your layout if you are using a cs-7

make sure you layout at 180 degrees, see how it shows up on your alignment grid, then mark it up at 90 degrees with the same 180 mark. then go 5 in and 5 down/up and measure to make sure that it is 5mm from the 90 degree or 180 mark to the 5in/down mark.