Anyone Ever Make A Franklin Bifocal?

[John@OWDC]

Looking for a way to bond-fuse-glue two lenses together to form a specialty lens for a patient.

Anyone find a glue or similar product that will cleanly and clearly bond CR-39, poly, or Trivex?

Strong enough to edge after bonding?

Thanks,
John

[Fezz]

I am sure that Chip or Jacqui will be along to tell you that you don't need adhesive if you do it like they do.

I have not tried to cement a franklin, but I would contact these guys if I wanted to.

http://www.optical-cement.com/

[John@OWDC]

Thanks Fezz!

[doctorjmjb]

I once had a pair of 18th century bifocals in my hands and got a real good look at how they were made. The frame was a small pewter oval with flint glass lenses. They were not bonded at all but two separate pieces clamped together and held in place by the eyewire. The two single vision lenses were cut in half precisely enough to fit perfectly together. Great craftsmanship! I, myself have a single vision pair with original lenses from the same era.

[chip anderson]

It's done like Dr. JmJb said but it's a whole lot easier with plastic. You an use a disc sander if you're very careful. Best to do it wih a few scrap lenses for practice before screwing up the real thin. Especially if the finished procuct is going to use expensive blanks. And like the man said, no bonding needed unless you are going to try a rimless, which I wouldn't advise.

Chip

Odd how so many very simple things like this one which was the first of it's kind and made with old antiquated techniques, is treated like it was rocket science by us edumakated types with cutting edge technology.

[rbaker]

We had to make a number of Franklins and cement bifocals in school back in the sixties. We used Canadian balsam to bond the two (or three if you were making a Franklin trifocal) lens segments together. You could edge the lenses into a zyle or metal frame with a minimum of pressure and usually beveled on a hand edger. Round or flat top or curved top segments were bonded to the distance carrier with Canadian balsam. We also fused some bifocals.

This was good training and really made us appreciate how far lens technology had come. It also gave us the skills to fabricate just about anything such as +8.00 diopter segs with 8DBI prism. And, all with little more than a hand pan and some pitch.

Ahhh . . for the good old days.

[price]

We used epoxe to fuse the lens together. Work well.

[chip anderson]

Note on Baker's comment. Canadian Balsam works on glass for cemented segments (if you could find someone today that could actually grind a wafer segment to glue (its soluable in Zylene for clean-up). But I am not sure that Canadian Balsam is suitable for plastic lenses.
I actually think Super Glue would work well on plastic lenses if you are super-super carefull and have some acetone for clean-up ready before you start glueing. Also note don't smoke with the Acetone open, and don't use any of the super glue or acetone on Poly. But I think it works fine on CR-39.
Whether you bond the lens halves together or not, you still need a perfect fit between the lenses and the frame before even concidering bonding them. Really rather doubt any sort of bonding material could be edged after bonding.
Also note, I mentioned earlier using some "dummy lenses" to practice with before jumping in to make the final product.
The flat bonding surface must be absolutely flat both side to side and at exactly flat side to side.
If you use bonding this will present a shinny surface and the patient will have a lot of trouble with glare from same (Jacqui adds some paint to adhesive) I don't bond and leave this surface frosted.

Chip

Unfortuately I didn't read all of your first post. Each pair of lenses should cut, edged, fitted in frame and marked at 180 degrees before you even concider splitting. The though of doing this right expecially with a high difference in top and bottom lens, bonding and edging is beyond the limits of present and past machinery. Trust me you will just end up with an expensive pile of scrap.

[Jacqui]

I actually think Super Glue would work well on plastic lenses if you are super-super carefull and have some acetone for clean-up ready before you start glueing. Also note don't smoke with the Acetone open, and don't use any of the super glue or acetone on Poly. But I think it works fine on CR-39.
Whether you bond the lens halves together or not, you still need a perfect fit between the lenses and the frame before even concidering bonding them. Really rather doubt any sort of bonding material could be edged after bonding.
Also note, I mentioned earlier using some "dummy lenses" to practice with before jumping in to make the final product.
The flat bonding surface must be absolutely flat both side to side and at exactly flat side to side.
If you use bonding this will present a shinny surface and the patient will have a lot of trouble with glare from same (Jacqui adds some paint to adhesive) I don't bond and leave this surface frosted.

Chip

Yup

[Jacqui]

I usually use an adhesive from the diamond industry that dries very dull on plastic, works very nicely for Franklins, hemianoptics, etc. At one time I used standard 2 part epoxy with a bit of powdered tempra paint added to reduce the glare. Glare is the big concern when gluing lenses together, it can cause lots of problems for the patient if it's not controlled.

Canadian balsam resin was used for glass lenses for about 200 years. It was used to cement Franklins, glue wafers on to make your own Kryptoks, etc. One pair that is in the Smithsonian that were made by Ben Franklin seems to be glued with it.

P.S. The tempra paint can be found at hobby stores like Ben Franklin, Micheal's, etc. It is used by grade schools, Scouts for art projects.

[Jacqui]

Looking for a way to bond-fuse-glue two lenses together to form a specialty lens for a patient.

Anyone find a glue or similar product that will cleanly and clearly bond CR-39, poly, or Trivex?

Strong enough to edge after bonding?



Thanks,
John

Edge first and then fit them together