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I think the vast majority would agree on Trivex and/or polycarbonate, but I am curious as to what specific property in Trivex makes it superior to Polycarbonate in terms of not cracking......and to that extent, what specific property of CR39 would make it the worst for drill jobs lenses?
:confused:
Many people wear CR-39 drilled rimless for many years without breakage. Same is true for all other materials including glass.
Other people can break any material except Trivex in a matter of weeks.
Chp
Trivex. Period.
Anything but poly
Poly is soft and the holes elongate over time.
CR-39 I think is more brittle. It would be ok if the bushings never loosen such that they have to be squeezed back down with the silhouette tool- I had one crack all the way across the top and learned my lesson.
But what makes Trivex "harder" than Poly and both "harder" than plastic.....it's not anything having to due with the index value so what is it?
Neither poly or Trivex is harder than CR-39. If hardness were of value here glass would be the material of choice.
The "virtue" of Poly and Trivex is it's more flexable, therefore doesn't break easliy on impact or when stressed.
Poly is actually the softest and most scratchable product we use for ophthalmic lenses.
Chip
Quote:
Originally Posted by chip anderson
YES! you can picture trivex kinda like those black hard rubber combs that were around when i was a kid (not THAT long ago), the suff is almost like rubber, it melts, its more flexible than any material, but its as clear as glass!
I think Trivex is a safer lens than poly in every way. I have seen others that use 1.67 and higher for drill jobs, but I've had a few of those crack. So, for here anyway, if you want a drill mount, you WILL get Trivex only!
Okay that makes sense. Thanks for the answer!Quote:
Originally Posted by chip anderson
Drilling has always been a big factor in rimless mounts. Even at the time there was only glass drilled with a diamond.
Vision-Ease Lens, Inc.
TECHNICAL SERVICES DEPARTMENT
DRILLING:
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Polycarbonate cuts best with a sharp burr operated at low speed and minimal to moderate pressure. Twiststyle drills, cutting less aggressively, often leave subsurface damage.
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Place lens with front towards drill bit and slowly operate drill through lens; back drill bit out of hole often to remove cutting debris that will increase heat damage.
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Be sure to chamfer around the hole when finished drilling. (Much like safety beveling after edging)
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Note that excessive pressures and speed create damaging heat, which may create eventual fractures.
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An extra precautionary step to avoid fractures would be to place a drop of OMS Drillseal into the hole. Distribute the Drillseal evenly with a toothpick. This will seal the hole and it dries instantly. Please note the dropper may gel if left in the bottle.
source:
www.vision-ease.com/Portals/VisionEase/.../LensDrillRimlessMounts.pdf
File Format: PDF/Adobe Acrobat - Quick View
You can also send messages to Technical Services via e-mail: techservices@vision techservices@vision-ease.com. POLYCARBONATE LENS DRILLING FOR RIMLESS ...
I would have to say it depends also on the mounting.
I have dozens of older Rodenstock rimless and Minima rimless out there...all made with CR-39...that still function well and have resisted cracking/breakage. Of course, it also depends on client handling. But it seems that rimless mountings that support the *front* side of the lens with a flat plaque help reduce flexure/tension cracks on all lens materials.
At least this is my experience.
B
There is more than one property that makes trivex superior to poly in terms of cracking:Quote:
Originally Posted by David_Garza
1. Trivex has a greater tensile strength
2. Trivex is more solvent resistant, so you do not have to worry about anything seeping into the drill hole and causing cracks.
3. Trivex has a lot less stressing, especially around the compression mounting.
It seems like 1&3 would fall under the previous answer of a more flexible material.Quote:
Originally Posted by Ocular Dexter
I'm not so sure about your conclusion. This YouTube video show the flexibility in an impact resistant test and you can see from the video, that there is a greater depression (oil can effect) during impact of the poly lens than there was for the trivex lens: ttp://www.youtube.com/watch?v=knnSKVROtzA&feature=youtube_gdata_playerQuote:
Originally Posted by David_Garza
I don't see the correlation between solvent resistance and flexibility, can you explain?
You don't see the correlation because what I meant was #s 1 & 3 were the same thing as the previous answer of being the most flexible of the materials......