Cribbing to frame shape?

[gweinrib]

Is anyone aware of any generators that posses the ability to crib a lens to the frame shape (or a close approximation)? If so, what is the benefit? I know elliptical or oval cribbing has existed for years. Was having a conversation regarding this recently and was wondering if anyone is doing this.

Thoughts?

[Chris Ryser]

No thoughts needed for this one .......................

Is anyone aware of any generators that posses the ability to crib a lens to the frame shape (or a close approximation)?

Thoughts?

No thoughts needed for this one .......................

A lens is blocked to have its surface worked on, which prevents the work needed to shape its edges.

[gweinrib]

No thoughts needed for this one .......................

A lens is blocked to have its surface worked on, which prevents the work needed to shape its edges.

Untrue... conventional (round) cribbing and oval/elliptical cribbing both do work to shape the edge of a surface blocked lens.

[Lab Insight]

Is anyone aware of any generators that posses the ability to crib a lens to the frame shape (or a close approximation)? If so, what is the benefit? I know elliptical or oval cribbing has existed for years. Was having a conversation regarding this recently and was wondering if anyone is doing this.

Thoughts?

There are no systems I'm aware of today that crib to frame shape. Oval and round cribbing are the norm. There is no real advantage (even on edging) to matching frame shape even it if it could be done, since the proper cribbing only leaves 1 to 2mm for layout overhang.

On another topic, are you a Geddy Lee fan?

[optical24/7]

MEI edgers crib lens excess to shape prior to final edging. But, yea, I haven't heard of a generator that cribs to lens shape.

[gweinrib]

On another topic, are you a Geddy Lee fan?

Very astute. Just a remarkable coincidence.

[Lab Insight]

Very astute. Just a remarkable coincidence.

He is a remarkable person and philanthropist. I've had the privilege to manufacture his lenses back in the day.

[Quince]

Interesting concept. I don't even have a tracer set up on my surfacing side (which would make my life much easier...) but I can see what the others are saying about it not being practical to finish and generate at the same time. There would be way too much room for breakage/ error, especially if there is going to be any coating going on. Deblocking alone would be infuriating. I like to leave my blanks larger for this reason.

[jefe]

MEI edgers crib lens excess to shape prior to final edging. But, yea, I haven't heard of a generator that cribs to lens shape.

George, you gave me some advice about eight years ago about cribbing which I have continued to use to this day.

[lensmanmd]

Interesting concept. I don't even have a tracer set up on my surfacing side (which would make my life much easier...) but I can see what the others are saying about it not being practical to finish and generate at the same time. There would be way too much room for breakage/ error, especially if there is going to be any coating going on. Deblocking alone would be infuriating. I like to leave my blanks larger for this reason.

Cribbing has many advantages. Prior to “smart” generators, we used to hog down blanks prior to layout and blocking. High RXs benefitted from this, as the fining and polishing times could be reduced. We saw lower aberrations and greater power yields. It did take a few minutes longer to calculate, and additional wear and tear on our Weco 440 edgers, but the results were worth it.
Fast forward to today.
All of our frames are traced and stored in LMS, prior to calculating. Our Orbit is set to elliptical cribbing, as it is our free form king. Our Cobalt is set for round cribbing. This improves polishing yields and reduces edging time, as well as slippage with our AR coatings.
I highly recommend tracing prior to surfacing.
As for cribbing to lens shape at the generator, I’m sure there will come a day when this will become practical. For, now, however, I see nothing but headaches.

[Quince]

lensmanmd, I completely agree! (as per usual)

I've expressed how a tracer can bring down redos and make a better looking product as well as save me time and stress, but my lack of funding and the notion of 'I've made it this long without' is an exhausting road to go down.

I am lucky enough that the majority of my orders are from within the building so I can simply hunt down the frame and eyeball my work. Not the best method but it is more helpful than when I have to Google frames so that I can then make guesstimations!

[lensmanmd]

I hear you Quince. Obtaining funding is tricky.
Best method is to look at your breakage rates and costs, then calculate the waste over a five year period. Then, take a look at good tracer costs and amortize the cost over the same five year period.
Santinelli tracers, IMO, are the best available, but can be costly. Huvitz and Optronics make good tracers that are more reasonably priced for independents.
Do a cost analysis to present to the ownership. Remember to add labor costs to the breakage costs. Redo costs are more than product costs, paid hours are a part of this, as well. Guaranteed that ROI will be recognized in less than 3 years, plus, equipment costs can be written off over 5 years. Money talks.

[Lensman11]

Hi
it is not difficult to get most generators to read a shape file. I actually did accomplish this about 7 years ago with the goal in mind of reducing processing time both in surface and finish. It did not work as planned. It is almost impossible to polish a non symmetrical shape. The long corners will not polish and will most likely induce prism. The closest process in use that I know is complex cribbing that will eliminate knife edges to reduce pad failure from the lens cutting the pad. The shape does not resemble any fixed shape as the right and left could have very different knife edge positions. This is intended for free form only not conventional surfacing.

[Lensman11]

I forgot the other major problem being 7 years have passed. Many frames are smaller than the the surface block diameter so you would have to default to a larger crib sizes in those cases. You really do not want to block smaller than 54 mm block as you lose support on the lens and you have to slow the generator to prevent de block. You would lose all the presumed time saving and increase spoilage do to using small blocks.

[gweinrib]

Thanks for all of the input. Some excellent points. I would like to clarify that I am not referring to edging in the generator, but, rather cribbing or shaping the lens something close to the frame shape in the generator. A few mm larger perhaps. Let the edger do the fine detail work.