Trivex or 1.67 in Rimless drill mt.

[jeffsoptical]

I have a customer that is very unhappy with cracking lenses in poly in her drill mount frame. Her Rx is about a -5.00 ou add +2.00ou. What would you recommend in a progressive? (Younger Image trivex or 1.67 Image) Are there differences in the 1.67 resin in progressive lenses?

Thanks,
Jeff

[rsandr]

I have a customer that is very unhappy with cracking lenses in poly in her drill mount frame. Her Rx is about a -5.00 ou add +2.00ou. What would you recommend in a progressive? (Younger Image trivex or 1.67 Image) Are there differences in the 1.67 resin in progressive lenses?

Thanks,
Jeff

In the Rx you describe I am sure a 1.67 would be robust enough.
I rarely have a problem with 1.6/1.67 into rimless these days.

[Optical Enigma]

1.67 has a similar impact resistance to poly (although less). It will not crack as poly does. Trivex has a lower Index of refraction and hence, will be thick.

[nickrock]

any 1.67 in MR-10 resin will have a very good tensile strength, although Trivex is guaranteed against cracking from some manufactures like Younger Optics, but is significantly thicker because of a lower index of refraction. Assuming not much other than what you have stated, I would opt for putting the patient in 1.67
Just my 2 cents

[rob.optician]

If the patient is already very upset about their poly lenses cracking - I would inform them that Trivex is much stronger (I have not had problems with it in rimless) but it is a little bit thicker than what they are used to. If they have a
-5.00 drilled rimless in poly to begin with - it sounds to me like they are not that concerned about the thickness of their lenses.

[For-Life]

If the patient is already very upset about their poly lenses cracking - I would inform them that Trivex is much stronger (I have not had problems with it in rimless) but it is a little bit thicker than what they are used to. If they have a
-5.00 drilled rimless in poly to begin with - it sounds to me like they are not that concerned about the thickness of their lenses.

I have gotten -5.00 very, very thin in a drilled rimless poly.

But the problem here is the micro cracks in the poly. There is a substance that will fill in those cracks upon drilling and then the problem will not happen. However, at this point it is best to switch them.

If you give them 1.67 you will offer a thinner product and increase the value that was hurt by the cracked lenses. 1.67 is not as impact resistant as poly or trivex, but is extremely durable.

[lensgeek]

Tensile strength certainly factors in when choosing a material for a 3 piece mount, although the problem here sounds like fractures from the polycarbonate material itself, not abuse by the wearer. Trivex is the best solution for overall performance in a drill mount frame. This particular Rx will not have as thin a profile as 1.67, but keep in mind, not all 1.67 material resins have equal tensile strengths. Manufacturer's high index materials can differ in formula from each other....ask for a MR-8(1.60) or MR-10(1.67) if the thickness is more important to the patient than overall durability.

[For-Life]

Tensile strength certainly factors in when choosing a material for a 3 piece mount, although the problem here sounds like fractures from the polycarbonate material itself, not abuse by the wearer. Trivex is the best solution for overall performance in a drill mount frame. This particular Rx will not have as thin a profile as 1.67, but keep in mind, not all 1.67 material resins have equal tensile strengths. Manufacturer's high index materials can differ in formula from each other....ask for a MR-8(1.60) or MR-10(1.67) if the thickness is more important to the patient than overall durability.

I was under the impression that the MR-10 is only a slight, probably unnoticeable improvement over the MR-7

[Audiyoda]

1.67 has a similar impact resistance to poly (although less). It will not crack as poly does. Trivex has a lower Index of refraction and hence, will be thick.

Similar?? Not even close - although 1.67 has plenty of tensile strength to be drill mounted, it is not an impact resistant material.

[lensgeek]

Now if you are talking about impact resistancy, high index materials are out of the race. My point was to compare alternatives to drilling polycarbonate while keeping in mind that MR formulas can differ, not only in tensile strength, but in ABBE and impact resistancy....taking it all into consideration...if you want all three: 1)Best optics 2)Impact resistancy 3)High tensile strength Offer Trivex!

[Chris Bowers]

It’s time we all take some responsibility for this. We are selling a product that by any other engineering method/standard would be considered insane. Would you buy a car that had the windshield attached with four 9/16 inch bolts? Would you buy fine China with the handles attached with screws? The only other lens type device I know of, that has holes in it, are large mirrors mounted on walls. Even so most are supplemented with a glue backing.



Consider three lenses, all of which have a circumference of 150mm.

• Standard “V” bevel having a support area of (frame contact area * circumference) approximately 225 square mm
• A groove mount having a support area of .5* ((.8 pi)*150)) or approximately 188 sq mm.
• A four hole drill mount using the formulae 2(pi r 2) + (2 pi r)* h so on a 1mm hole at 2mm depth we get 7.85 sq mm and again * 4 holes we have a total support area of 31.4 sq mm

I would also think that with two holes fixing the mount, only the hole closest to the temple or bridge are taking any force. Or we have reduced the surface mounting area to a mere 15.2 sq mm.



Next consider the frame that uses the temple as a type of leaf spring. Yes they absorb energy but at a cost. In the worn position they continue to put stress on the outside holes. This long term stress is very bad for poly products.



We have come along way and most of the bad mounts are gone. Products like Drill Seal have helped immensely but we are still dealing with a fragile product.



Maybe we should look at the drilled rimless much like we do a bikini. So little material, so much cost. (Please leave this one alone guys)



Caveat Emptor or is it bewear?

[chrome surfer]

Now if you are talking about impact resistancy, high index materials are out of the race. My point was to compare alternatives to drilling polycarbonate while keeping in mind that MR formulas can differ, not only in tensile strength, but in ABBE and impact resistancy....taking it all into consideration...if you want all three: 1)Best optics 2)Impact resistancy 3)High tensile strength Offer Trivex!

I agree with what you are saying sometimes edge thickness isn't as important, evaluate the options like going to court.
Yvette

[loncoa]

Personally I think the retentives in the crowd might be overthinking this a bit. I've mounted literally thousands of these in Poly with less than 1% having problems with the mounting. Trivex will be too thick and honestly patients with a -5.00 are not happy going to an unsightly lens to try to gain tensile strength. At least not any I've met. 1.67 will be fine. MR-10 or MR-7 have shown very little difference (to us) in overall performance. That is, if they are mounted skillfully and correctly. I will leave it to your judgement as to whether that is the type of work you are receiving or not.

[Pete Hanlin]

I couldn't agree more with Ioncoa... Assuming proper processes are used, none of the materials mentioned in this thread (Trivex, Polycarbonate, either of the 1.67 varients) should be problematic in a drill-mount setting. Personally, I have abused and worn my Minima drill mounts with CR-39 polarized lenses for 3 years now with no chipping/cracking.

Trivex is certainly an excellent material for drill mounting- from the aspect that it does the best job of overcoming a poor mounting. Tensile strength does play a role in the durability of a lens material when mounted in a drill setting. Basically, a small crack in the edge of the hole (a crack propogation point) will be less likely to expand through the lens if the material has a high tensile strength.

When mounting polycarbonate (or any other material) in a drill setting, these propogation points result when the mounting holes/notches are not chamfered. That is, the cracks usually occur in the hard coating. Experiment time- take a sheet of ordinary paper... pull on the two sides. You can actually pull pretty hard without tearing the paper. Now, make a tiny tear in the top edge of the paper and pull again- the paper tears much more readily. The tear represents a crack in the coating. Chamfering removes the crack- and therefore the propogation point.

Additionally, the hole position and size must be properly positioned and sized to acheive a durable drill mount. A hole that is too large will encourage the optician to excessively tighten the mount- which usually drives the washer or nut down into the lens like a wedge. Also, pressure points are created by holes that are too large (as you open and close the frame, the screw wobbles in the hole- which of course drives the patient back in for- you guessed it- more tightening/wedging).

So, were this my patient, I would use a 1.67 (either the MR-7 or MR-10), which will be quite thinner than a Trivex lens. Again, however, you should be able to use ANY of the materials mentioned here to provide durable drill mounted eyewear (I have a presentation on the subject I've given at OLA and in our Laboratory University program- I would be willing to email portions of it to anyone who has an interest).

Pete
phanlin@essilorusa.com

[HarryChiling]

Consider three lenses, all of which have a circumference of 150mm.

• Standard “V” bevel having a support area of (frame contact area * circumference) approximately 225 square mm
• A groove mount having a support area of .5* ((.8 pi)*150)) or approximately 188 sq mm.
• A four hole drill mount using the formulae 2(pi r 2) + (2 pi r)* h so on a 1mm hole at 2mm depth we get 7.85 sq mm and again * 4 holes we have a total support area of 31.4 sq mm

Your rimless hole formula is slightly off. You are adding the surface aea of the top and bottom wich do not take the brunt of the force being applied when we look at rimless lenses. A more accurate formula would be the lateral area of the cylinder or drill hole.

2*pi*r*h

The groove mount formula is off as well. We could use the surface area of a circular ring then subtract a 1/4 off of thisto account for the bottom of the string not having contact with the lens.

(4*pi*r*R)-(pi*r*R)

R=(frame A + frame B)/2

R is the average radiius of the frames lens. This figure is not an accurate measure, but works with little error.

For the "V" bevel you could use the formula

2*circumferance*Sqr[(bevel height)^2+(bevel width/2)^2]

This formula assumes that the entire bevel is in contact with the frame and sits flush which is more often than not, not the case.

[Jim Stone]

Now if you are talking about impact resistancy, high index materials are out of the race. My point was to compare alternatives to drilling polycarbonate while keeping in mind that MR formulas can differ, not only in tensile strength, but in ABBE and impact resistancy....taking it all into consideration...if you want all three: 1)Best optics 2)Impact resistancy 3)High tensile strength Offer Trivex!

#4 thickness.
Sorry, not trivex. It's as thick as glass. Should be real ugly in a -5.00.

[Diane]

I've used them all over the years, and love the 1.67 for higher minus powers. Years ago, I used and wore CR-39 and never had a problem but it could be thick. Based on all the substantiated reports, CR-39 shouldn't be used today. Trivex was originally designed for rimless mounts, due to its tensil strength, but is much thicker. Poly is strong, but as has been mentioned, the cracks can appear, unless you use a sealant, such as the one that Chris Ryser offers. Also, when drilling poly, a sharp drill bit, run at a slower speed helps. Let the drill do the work, don't push...A slight chamfering of the holes should be done on any material. Duh...seems like the same things should be done on any material in processing the lens.

Anyway, 1.67 gets my vote...oh, and by the way, that's what I wear, now.

Diane

[Chris Ryser]

If using Polycarbonate you can always seal the crack with a drop of Drillseal and your lenses will not crack for that reason

Check it out at http://optochemicals.com/products/info_drillseal.htm

[Pete Hanlin]

Also, when drilling poly, a sharp drill bit, run at a slower speed helps. Let the drill do the work, don't push...A slight chamfering of the holes should be done on any material. Duh...seems like the same things should be done on any material in processing the lens.

Spot on as usual, Diane! Unfortunately, I've seen many failed jobs with no chamfering (what amazes me is when someone sends in a job that has been "remade four times"). I notice there is no chamfering, call to point it out, and am told something like "Oh, we don't usually do that!"

Um, supposedly you remade it for the fourth time- even if you don't "usually" perform this crucial step, it would seem someone might think of it the second, third, fourth time around!

Great comment on the drill speed and sharpness of the bit. Polycarbonate is a thermoplastic (like glass, actually). Therefore, when you do not heed Diane's advice and use excessive pressure (or a dull bit), heat builds up in the lens. Eventually, the heat builds to a point where the poly begins to re-liquify (which only a thermoplastic will do- 1.67, CR-39, etc. will never re-liquify). As the poly re-cools/hardens, small fissures form within the material- which are crack propogation points.

[jeffsoptical]

Thanks for all the advice from different members. I'm going to use an Image 1.67 in her drill mount frame. I found out that it is MR-10 resin.:bbg: