Required Thickness for Grooved Rimless in Plus Lenses

[JSD]

For you seasoned guys with tons of experience edging I would love to get some feedback. When doing grooved rimless jobs for minus lenses, required minimum edge thickness seems not to be a problem. When doing plus lenses is there any rule of thumb or guidelines for achieving adequate edge thickness to place a groove without going too thin to provide proper lense integrity? How would you decide when to use stock lenses vs when to have your uncuts surfaced? Thanks to all for sharing your experience. Hoping this is not considered a dumb question for you guys that have run 100+ jobs daily.

[Tallboy]

Its definitely material dependent ... and patient dependent. As a rule at least 2.2 thickness is a good amount if your are grooving a 6mm groove, that leaves .8 on the front and back of the groove, more than enough for a trivex or poly lens.

2.5-3.0mm for CR39 depending on how risky you want to be.

No dumb questions about lens processing on Optiboard as long as you don't say my questions about Optics are dumb!

[JSD]

Thanks for the good response Tallboy.

So let's say we have an Rx that is +1.00 or say +3.00. When ordering stock lenses we seem to be able to get 65mm blanks or I believe 74mm aspheric. Our other option is ordering surfaced uncuts. How do you determine what blank will give your the desired 2.2 thickness for your job at it's thinnest point? BTW--I believe my unit is currently set for a groove width of 0.07mm.

[Tallboy]

When ordering stock lenses we seem to be able to get 65mm blanks or I believe 74mm aspheric. Our other option is ordering surfaced uncuts. How do you determine what blank will give your the desired 2.2 thickness for your job at it's thinnest point? BTW--I believe my unit is currently set for a groove width of 0.07mm.

.07 is a fine groove width, just accommodate the mm accordingly. As far as the blank size unfortunately only calculating the "minimum blank size" (try http://64.50.176.246/tools/blanksize.php) then using experience to decide.

Some brands and materials will have different edge thicknesses at the end of their blank. See a SOMO stock poly will have one edge thicknes (usually a little thicker) and a Crizal will be very thin at the edge of the 65mm, zeiss and seiko seem to be in the middle. You have to take this into account. Unfortunately only experience will help you because all wholesale labs will just tell you to get it surfaced.

A rule of thumb I use is if the blank is 65mm, and the MBS (minimum blank size) is at least 57 or so there should be plenty of room. Be careful pushing this limit with poly because you may finish it well, and the client will return later with splitting along the groove looking like starbursts.

Good luck!

[PRECISIONLAB]

As a 100+ lab guy, I would recommend ordering uncuts on powers with +2.75 and stronger. Stock plus powers 2.50 and below in either CR-39 or poly seem to yield desirable results for groove type frames but past this break point lenses appear thick not to mention are processed on ideal base curves. For example a +3.00 cr-39 stock will have a 5.2 center ground on a 8 base curve as opposed to lab grind...6 base with an average thickness of 4.0 based on average lens size. Ordering uncuts will result in an ideal thickness since minimum edge for rimless is accounted for. Factors such as lens size and shape , decentration , and minimum thickness based on lens total power are calculated resulting in a cosmetic appealing pair of glasses

[JSD]

Thank you again Tallboy and Precisionlab. Nice calculator on Opticampus. Sounds like a good rule of thumb on +2.75 & up.

[Chris Ryser]

How would you decide when to use stock lenses vs when to have your uncuts surfaced? Thanks to all for sharing your experience. Hoping this is not considered a dumb question for you guys that have run 100+ jobs daily.

No dumb question whatsoever ...........................

Essilor came out with their latest rimless frame idea with the "Nylor" frames in the mid to late 1950's and it became nearly instantly the big fashion in Europe.

Standard uncut lens size at that time used to be 55mm and finished lens sizes were also much smaller than these days.

European lens manufacturers very soon started to offer 62 mm diameter stock lenses so we could have thicker edges on the plus lenses when having to decentrate, due to PD issues.

[jefe]

If you're using Trivex, the minimum edge thickness can be lower than 2.2 -- perhaps 1.5mm. Sometimes, an edger will allow the edge to be slightly thinner, but it has to be calibrated well.

[AngeHamm]

This is also dependent on how well your edger traces and maps these lenses.

[Quince]

Our location runs 1.5-1.8 on most jobs (no CR39). That said, this is how our best tech prefers his work. The jobs I send to our sister location gets an average of 2mm.

[rbanting69]

What happened to your staff? 15+ years edging experience.