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Thread: Lab Question - Gerber/Coburn SGX Generator Related

  1. #1
    Bad address email on file donovanbaldwin's Avatar
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    Confused Lab Question - Gerber/Coburn SGX Generator Related

    Many years ago, 11 to be exact, I worked with a Coburn 108, I think it was, in an optical lab owned by an optometrist in Austin. We blocked with alloy. It was a small lab and I think Alley Oop trained me. Computers sent rockets to the moon, etc.

    I quit and went to do other things.

    Fast forward to the 21st century, and I have gone back into an optical lab and am re-learning pretty much from scratch. We block with wax, and a computer spits out the lab sheet and tells the SGX what to generate for the Rx.

    When I worked in the cave in the 1990's we had a small blocking ring with a cutout for the seg on the inside of the ring for lined BF's. We decentered manually and turned the inset and the seg ABOVE the 180 line of the block to prevent the alloy from running off through the cutout.

    In my present lab, it doesn't matter, as far as run-off of the wax is concerned, as the ring is big enough to include the seg, but I have been told that I must put the seg BELOW the 180 line of the block as much as possible as putting it ABOVE the 180 will cause prism.

    I am told that this is because the computer program has been written to assume that the seg is BELOW the 180, or on the bottom side of the block.

    I realize that a computer program can incorporate a lot of variables that I cannot consider and can use them to generate a lens, but will turning the seg one way or the other cause prism if the cylinder axis is blocked properly?

    Help?

    I can't think without my coffee!!!!

    Thanks,
    Don

  2. #2
    Professional Rabble-Rouser hipoptical's Avatar
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    The software calculates prism for decentration, and if you align the seg the wrong way, the OC will be in the wrong direction. Lab management systems can be a great tool or a pain in the rumpus, but since almost every lab around today uses them, you'll have to get used to it. Computers only know what they are told, and they make calculations based on that info. The input data must be based upon known constants, and lens orientation is just one of those constants. The lens is aligned to the block, and the block has a set position on the generator. The LMS (lab mgmt system) has those positions set as defaults to calculate lens curves, OC, thickness, etc..
    Hope this helps.
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    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    Quote Originally Posted by donovanbaldwin View Post
    Many years ago, 11 to be exact, I worked with a Coburn 108, I think it was, in an optical lab owned by an optometrist in Austin. We blocked with alloy. It was a small lab and I think Alley Oop trained me. Computers sent rockets to the moon, etc.

    I quit and went to do other things.

    Fast forward to the 21st century, and I have gone back into an optical lab and am re-learning pretty much from scratch. We block with wax, and a computer spits out the lab sheet and tells the SGX what to generate for the Rx.

    When I worked in the cave in the 1990's we had a small blocking ring with a cutout for the seg on the inside of the ring for lined BF's. We decentered manually and turned the inset and the seg ABOVE the 180 line of the block to prevent the alloy from running off through the cutout.

    In my present lab, it doesn't matter, as far as run-off of the wax is concerned, as the ring is big enough to include the seg, but I have been told that I must put the seg BELOW the 180 line of the block as much as possible as putting it ABOVE the 180 will cause prism.

    I am told that this is because the computer program has been written to assume that the seg is BELOW the 180, or on the bottom side of the block.

    I realize that a computer program can incorporate a lot of variables that I cannot consider and can use them to generate a lens, but will turning the seg one way or the other cause prism if the cylinder axis is blocked properly?

    Help?

    I can't think without my coffee!!!!

    Thanks,
    Don
    What kind of blocker do you have? I'm guessing, not a Step One, because then, you would simply align the seg with the image on the screen.

    In any case, what really matters is how you chuck the lens in the generator - the SGX has a setting for "seg down" or "pin down" - if you're not using the Step One, or Gerber blocks, the usual procedure would be "seg down". If you are using a Step One, the setting on the blocker and generator must agree.

    ...if I recall correctly...

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    Bad address email on file donovanbaldwin's Avatar
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    Thanks for the info. Gerber blocks; red, blue, gray, etc. Not a Step one as far as I know.

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    I use an SGX daily. Our computer system specifes layout instructions based on each lens's specific design. For example, one of the ST28 jobs I did today was to be blocked 6mm in and seg line 6mm down. This basically geometrically centers the lens on the blocker. The generator then decentered the A 2.5mm and the B 1mm. I don't know the software you use, but I would think it should specify layout for blocking as ours does.

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    Bad address email on file donovanbaldwin's Avatar
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    Right. I get the x in and y down, decenter accordingly in the marker, and mark the axis. However, my question is, when I lay the lens on the ring, over the block, and prepare to run the wax, does it matter if I turn the seg so that it is in the lower portion (as I am looking at it) of the ring or the upper?

    For example, FT28 cyl axis 180. When I lay the axis along the horizontal marks, does it matter if the seg points up or points down? What if the axis is 98 or 85 where perhaps only a portion of the seg is above or below the line depending on how I rotate it?

    When I manually decentered years ago, I was marking where I wanted the OC to be, and blocked so that the center of the alloy block was at that point and then generated the lens. However, today's technology allows the computer to make decisions about how it is going to create prism, for example. Since I was setting the OC manually back then, it did not matter if I turned the lens one way or the other as long as the axis line of the lens agreed with the 180 line thru the middle of the block.

    Is the software or generator assuming that I have rotated the lens one way or the other so that all or some percent of the seg is below the axis line of the block?

    Have a heart, man. I'll go mad! Where did you hide the coffee????

    Don
    Last edited by donovanbaldwin; 09-02-2009 at 07:21 AM.

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    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by hipoptical View Post
    The software calculates prism for decentration, and if you align the seg the wrong way, the OC will be in the wrong direction. Lab management systems can be a great tool or a pain in the rumpus, but since almost every lab around today uses them, you'll have to get used to it. Computers only know what they are told, and they make calculations based on that info. The input data must be based upon known constants, and lens orientation is just one of those constants. The lens is aligned to the block, and the block has a set position on the generator. The LMS (lab mgmt system) has those positions set as defaults to calculate lens curves, OC, thickness, etc..
    Hope this helps.
    That about sums it up, your not marking the OC, your now marking the GC, geometic center of the lens and the software moves the OC in relation to where the GC is on the lens. Prism is described in 0 to 360 and axis is described in 0 to 180, so if the axis is supposed to be 45 you could also have the axis at 225 and the power remains the same. This is not the case with prism if you had a 45, you have for instance 2BI and 2BU prism, where as 225 would be 2BO and 2BD, the opposite. So like hipoptical mentioned the lens must be positioned as a constant in the machine so the software knows in which direction to cut the prism, which decenters the lens.

    When lenses were marked on OC, you could flip the lens any which way your heart desired since the only axis this would effect would be the cylinder axis, but the operator still made sure to decenter correctly they didn't consider positive decentration and negative decentration the same thing.
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    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    As I wrote earlier, it is the generator that assumes a certain rotational orientation - that the lens was loaded either "seg down" or "pin down", depending on a configuration setting on the SGX. The chuck of the SGX rotates appropriately, depending on that setting, when the job data is retrieved from the LMS. The LMS sends the same data either way - it is ignorant of the pin down/seg down setting; for that matter, there is no facility for the LMS to send the pin down/seg down setting.

    If you are using "pin down", the orientation of the block on the blocker matters. The "pin" in this case corresponds to the oblong hole on the block. Gerber blocks have one oblong hole and one round; the old Coburn aluminum blocks did not. The SGX accepts either.

    If you're using "seg down", the orientation of the lens on the blocker shouldn't matter - though I can't recall offhand for certain if the block can be inserted incorrectly in the SGX (that is, with the pin in the chuck aligning with the round hole in the block); I think it can, otherwise it wouldn't accept Coburn blocks, and it definitely does that.

    Does that answer your question?

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    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by shanbaum View Post
    As I wrote earlier, it is the generator that assumes a certain rotational orientation - that the lens was loaded either "seg down" or "pin down", depending on a configuration setting on the SGX.
    Let me clarify my earlier post, the generator assumes orientation, the software calculates the amount of prism to decenter the lens. My post may have been a bit confusing in the wording, the generator does none of the thinking, it is set to accpet the lens in a certain way, the software does the thinking.

    though I can't recall offhand for certain if the block can be inserted incorrectly in the SGX (that is, with the pin in the chuck aligning with the round hole in the block)
    It can, if it's aligned right with the gerber blocks the block locks in. If it's put in without the pin aligning right the block could rotate.
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    It shouldn't matter where the seg is as you block it as long as you use your layout marks to align the axis and geometric center. As others have said, make sure you put it in the chuck the way the generator expects it, i.e. 'pin down' or 'seg down'. We keep ours on 'seg down' as this gives us the extra verification step of visually confirming lens position before the 'start' button is pushed. Seg down, seg line horizontal, ready to generate.

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    Bad address email on file donovanbaldwin's Avatar
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    Thanks to all. Your comments have made it clearer to me....but another cup of coffee would really help a lot!:cheers: ...or whatever!!
    Don

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