Recommendations for Lindberg Frame

[dave235764954]

I was wondering what it is that is causing the below cracks to form in this lindberg frame and if there are any adjustments in the edging process to minimize these internal fractures/cracks from forming?

https://www.youtube.com/watch?v=7uIXySSVWsI

[merrymaker]

It looks like a combination of the material (poly?) and edging the lens thickness down too much so that the grooved 'shelf' is so thin that it easily chips when the frame bends and shifts.

Hope the below image helps:

[Dirk]

The most obvious causes would be lens material and groove width. Material should be 1.6 ( I have been advised not to use polycarbonate), groove width 1mm, lens width min 2 mm. Another cause is the square shape of the groove, the rim has a round shape, that causes tension. Lindberg advises to file the groove first, they have a special tool for it.

I hope this is helpful.

[Craig]

We never have that issue while we use lenses down to 1.6mm and cut the 1.0mm groove to match the frame curve but we only use trivex.
Any other material will cause you to make to extra thick to avoid the eventual cracks; the lenses all get more brittle over time.

We also use an ME1200 machine but the real issue is material selection of anything but trivex.

[Dr. Bill Stacy]

I agree that Trivex will eliminate this problem. However, the chipping is so bad I can't believe it's poly. I'm betting CR39. If so, never use CR39 in a groved metal mounting. It's almost guaranteed to fail.

[dave235764954]

Yeah, these were made with poly -- if the customer slept in them, would that have been the cause of this? if there were made optimally with Trivex, could the patient safely fall asleep (i.e., head on side, applying pressure on one side to the frame) while wearing them you think?

[Dr. Bill Stacy]

Yeah, these were made with poly -- if the customer slept in them, would that have been the cause of this? if there were made optimally with Trivex, could the patient safely fall asleep (i.e., head on side, applying pressure on one side to the frame) while wearing them you think?

I've never seen poly chip like that, but those Lindberg frames are unforgiving for sure; make sure the groove is wide enough and deep enough, but I'd double check that material (remove a lens and drop it on a tile or other hard surface and listen for the distinctive tinny ping you get with poly, more of a dull thud with cr39). But yeah, Trivex is nearly bullet proof.

[dave235764954]

assuming the lenses are remade by the lab in Trivex and cut optimally, do you think the customer could safely fall asleep while wearing them without having these cracks form? (i.e., falling asleep causing extra pressure between frame and lens)

[newguyaroundhere]

I would advise the individual to not fall asleep in the glasses

[Craig]

If you get trivex at 2mm edge and put in a 1mm groove; it is good as it gets. It is important to put in a groove that is clean and accurate but if done properly there is no reason for trivex to fail under normal circumstances.

We use 96% trivex and Lindberg is our number 1 collection with 70% drill mounts out of all of our sales. We are the guys who love all things that most shy away from.

[jefe]

I agree that Trivex will eliminate this problem. However, the chipping is so bad I can't believe it's poly. I'm betting CR39. If so, never use CR39 in a groved metal mounting. It's almost guaranteed to fail.

It looks like many poly lenses. CR-39 wouldn't crack so much -- big chunks would flake off instead. Trivex is most definitely the way to go.

[Dr. Bill Stacy]

Some labs won't even attempt to do cr39 in a metal grooved mounting. I might be tempted to try it in a -2.00, but +2.00? horrors...

[mdeimler]

If you use poly, you need to chamfer the sharp edges INSIDE the groove, kinda like safety beveling the inside of the groove. Otherwise this can happen.

[dave235764954]

Thanks for the replies guys - this appears to have worked perfectly (i.e., using trivex for these frames)