Plus tooling?

[RJEye]

Hi All,

I work with several opticians who feel plus tooling for highly hyperopic (over +8D) lenses provides a better finished product for the patient.

Our new lab (and many others I am finding out) do not manufacture lenses with plus tooling. I trust that there is a sound reason why they do not.

I'm trying to provide a technically sound explanation as to the benefits/drawbacks of specifying plus tooling.

What's your take? Can you point me towards any reference material?

Thanks!

[JRS]

Sometimes PLUS tooling is the only viable option for the specific lens you ask for - e.g. the Rx is +9.00 and the highest base available (made) is a 8.00 diopter.

Certainly there all other alternatives...in some cases. Using a difference index, a slightly different lens product, etc. That said, another reason for the PLUS tooling is to minimize the front curve. In some instances, if a 8.00 base (as in the above example, goes slightly PLUS on the rear, but your next base curve choice is a 10.00 base (with MINUS rear curves) which would serve the patient better. Typically, they don't much care for the bulge of the 10.00 base. Optically, the 10.00 base is the correct choice, but cosmetics certainly play a huge role in today's sales.

I should also add, that not all labs have PLUS tooling (laps). So they tend to shy away from those Rx's, or send them to a sub-contractor. It in no way diminishes that particular labs ability to do good solid, quality work for you, it's just a limitation of resources. Fining/Polishing PLUS rear surfaces is not quite as easy as F/P of MINUS rear surfaces. Some equipment handles those curves badly, and/or the few Rx's requiring PLUS rears does not warrant an investment in tooling, etc.

[HarryChiling]

In our small surfaceing lab I on occasion use a plus back surface and we use lap masters for it, but I can tell you even then like JRS menioned the equipment doesn't liek to cooperate with me at times, by that I mean the foam laps tend to break apart more easily due to the force being applied in the direction it does when polishing plus curves, I overcome this by wrappin the tools sides with you guessed it DUCT TAPE, but even then it doesn't always work, in the case of aluminum, steel or hard plastic tools it's a significant investmen in a not to commonly ordered product, not to mention that a back curve on a lens would create horrible off axis astigmatis.

[JRS]

Many years ago Harry... when most you weren't even a gleam in your dad's eye, we use to do cap work. You reverse the lap and the lens so the machines didn't struggle "quite" so bad. Even then they were tougher than standad work. but again, as I eluded to earlier, so times you have to make a choice and go with what you got.

Foam laps are, as mentioned by you, forced into pressures on the edges that they were not designed to take, and break up. Flats and some plus aren't too bad, but a convex rear over +2.00 or so starts to come apart. You could try pressure reducing to about 8 psi (or 0.55 bar) and monitor the timing.

Some day we'll have to meet someplace. I'd like to know you better. See ya Harry.

[HarryChiling]

Some day we'll have to meet someplace. I'd like to know you better. See ya Harry.

The first couple drinks will be on me. ;):cheers:

[Jacqui]

We do them here at times using plastic laps. There are still problems, but I think they are better than foam and cheaper than aluminum. The best way that I can see is to do them freeform with a soft lap polisher.

[rob in uk]

Plus tooling? What a pain up the a**e! we used to do plus tooling until about 15yrs ago. The worst blanks were the 38 seg whick often used chunk off the edge of the oblong edge on the final cut.In my opinion minus curves offer a better cosmetic finish.But we the odd plus and minus curve on the same tool which we call a saddleback but only on low powers but not by choice!!!

[chip anderson]

I guess those of us old nuff to have surfaced glass just don't get the concept. Never found much difference in surfacing and polishing plus or minus. The shorter the radius to be polished, the more difficult but only slightly so.

[Jacqui]

I remember polishing glass plus on a hand polisher (sphere polisher). Did many slab-offs, seg reductions, base curve changes, and polished moulded blanks, etc. I always loved doing them, no one bothered me while I worked. :D

[JRS]

Yes Chip, once upon a time, doing those was fairly straight forward. However, we had equipment meant for it - Strasbach (sp), R/H cylinder machines, sphere bowls, etc. But most of the small places today only have 50x types. And likely something like an Optek cyl machine. For us changing the stroke was a simple matter. Not easy on the simple designed pin type machines.

Besides, we grew up knowing how to do those - we did plenty and had practice. Not many get that education anymore. It's a shame really, but it is what it is.

[rob in uk]

Believe it or not we still have a hand smoother ( we used to call it a " poker arm", you may have known it as a pan handle)on which we used to hand roll the base/cross cyls that were out of range for the generator but we have not used it for about 5 years as glass is almost redundant over here, so is very scarce to obtain unless we go to Zeiss ect. which can be expensive. We still do the odd glass ( approx 2-3 pairs per month).

[billmdee]

Every once in a while we have made high plus lenses with Plus tools. I have successfully made them on both an SGX and 2G generators, using foam laps on the generator.

We only do them as a last resort, but the results have always been good.

[rob in uk]

On hi plus spheres we used to use "cap tools" do you still use them?

[Jacqui]

On hi plus spheres we used to use "cap tools" do you still use them?

Haven't seen one of those in years.

[shanbaum]

"Cap laps" are in fact a better way to fine and polish convex surfaces on most cylinder machines, most of which do not function particularly well outside a rather small range of concave surfaces.