Surfacing

[sandeepgoodbole]

The Surfacing process practised in India is being described here.
For Mass Production , the set up comprises of spherical/ Cylinderical Generators and polishers.
People having 30 -50 Pairs Rx Daily, do the job with 1/2 HP Motors
grinding the lenses on Cast Iron/ Diamond tools.
The process starts with Emery No 100/120 , 160/180 , goes thru 302,303 and finishes with Cerium Oxide / Red Oxide.
Blocking is done either with Alloy or Tar Pitch.
I have :
1. 2 Manual Spherical Sets with 1/2 Hp Motors.
2. 2 Semi automatic Sph. Polishers
4. 6 Cyl spindles. @ One HP motor running 4 cyl.spindles
and 0.75 Hp running 2 cyl. Spindles thru a line shaft, flat belts and flat pullies.
This is very old type of equipment. New types comprise of saperate motors for each spindle with V belts.
I want to know :
1.What new things Modern Technology has brought in the Rx Lab?
2.What is the optimum power requierment per spindle for Cylinders ? What are the optimum RPMs required for different stages and emeries ?

[John R]

What sort of machines are you running now?? Autoflow silwing 101's

Best bet for surfacing is coburn 505's and 506's we still use them. The new stuff just dont hack it compared to the old stuff.
Also we use diamond pads for smoothing, So much cleaner.
When we used emery for smoothing we only used on grade p15. We tryed 2 grades( p20 & p10) but the time saving was not worth the extra trouble involved. I think we smoothed for 6 mins then had a 8 min polish. Now with diamond smoothing ( 3 mins) we can cut polishing down to 6 mins.

[optispares]

Best bet for surfacing is coburn 505's and 506's we still use them.

and I thought you used 5055/6 for smoothing.
but seriously diamond smoothing when set up correctly is cheaper and cleaner, also less wear and tear on machinery.( no emery to get in the bearings when the sock lifts).:cheers:

[sandeepgoodbole]

John R said:
What sort of machines are you running now?? Autoflow silwing 101's

Best bet for surfacing is coburn 505's and 506's we still use them. The new stuff just dont hack it compared to the old stuff.
Also we use diamond pads for smoothing, So much cleaner.
When we used emery for smoothing we only used on grade p15. We tryed 2 grades( p20 & p10) but the time saving was not worth the extra trouble involved. I think we smoothed for 6 mins then had a 8 min polish. Now with diamond smoothing ( 3 mins) we can cut polishing down to 6 mins.

Hi John,
I was exepcting reply.
We use very simple machines, operated manually , made in India itself.
By the way what is the cost of production per pair for a lab processing 50 pairs daily ?
I am interested to know:
1.How many pairs a Diamond Smoothening Tool serves for ?
What is the Cost of the tool?
2.What is the RPM at which it is done.
3.What is the HP of the motor it gets power from.

[John R]

The diamond pads (sourced from the states) we use give us approx 250 surfaces, but we have just changed the cutting oil we use and are seeing much higher life from the pads up to 350.
I could not say what the cost per lens is as costing is not my field, all i can say is its cheaper than using smoothing emery.
As to machinery specs you would be better speeking to "Optispares" as its his field.

[myodisk]

Its good to know that there are some places left that know how to do it the hard (requiring skill and thought) way. Most modern labs in the US and Western Europe are set up in such a way that the equipment does most of the thinking, and "skilled" people are only needed to teach (train) the workers and troubleshoot the process or the equipment it self. I estimate my cost (consumables only, ie: alloy, pads, polish, wear on cutters, etc...) to be less than 50 cents per pair for CR39 and close to 75 cents per pair for glass and polycarbonate. Glass uses more diamond and "rare earth" products and Poly requires a back side coating to resist scratching.

As far as the labor, we have 5 people working 8 hours per day in the surface (grinding) room including the inspector and are processing about 300 pair per day of all materials. Our blocker does not require lay out marks as it has cameras and the computer to tell the operator that it is "in the right position to block" Our generator does not require any operator at all as it is loaded and unloaded by robotics.

We are more like a "lens factory" than a laboratory any more but it does make more money that way...... Sad......

I would love a "student exchange" program for our industry if we could get some one to pay for it.....

Myodisk

[sandeepgoodbole]

How much can you travel back in time, if you come to India !
The costs mentioned are running costs.
What does all those Robots, and the Lens Making Stations cost I wonder. Salaries to Mr. Spoks must be sky high as copmaired to the race down here.
Simillarly, margin of profit one gets there must be astronimically satisfying. It would be nice to explore whether those "Lens Trekers" can land and operate here as well. :)

In India, these days people are enjoying handsome returns by stupendus appriciation of the Land where the shops and factories are standing. So, what you earn by saling goods you make ,seems in the back seat.
Drifting back to technical point ..
Can somebody tell me what are the Optiumum values of the Pressure and the RPM required at different stages of Surfacing of Glass, Cr and Poly .

Lastly , 100 Cents= 1 Dollar if this equation is correct
Let me transcurrency it in our terms.
1 $ these days = @50 Indian Rs. = 100 Cents
Cost of Corning 60mm Plano 1.523 with all taxes and landing at our door = Rs. 18/- = 36 Cents. Does this sound ok at your end?

[shanbaum]

sandeepgoodbole said:
Lastly , 100 Cents= 1 Dollar if this equation is correct
Let me transcurrency it in our terms.
1 $ these days = @50 Indian Rs. = 100 Cents
Cost of Corning 60mm Plano 1.523 with all taxes and landing at our door = Rs. 18/- = 36 Cents. Does this sound ok at your end?

Hi, Sandeep,

So, how much would a Dodge Viper cost? On second thought, maybe "Viper" is not a great choice.

There's no direct answer to your question about speeds and pressures - speed, for instance, is related to how the lens is suspended, and the robustness of the mechanism overall. On the one hand, you probably think you want to go as fast as possible (time being money, though the exact equation may be different there) - the limiting factor will not be some characteristic of the abrasive process itself (such as, setting the abrasive pad afire, boiling the slurry, or melting the surface of the lens), but some mechanical limitation, such as the lens rocking in and out of its holder, or parts in the machine rattling loose. You'll encounter the latter at much lower speeds than the former.

Pressure is a somewhat different story, and it differs significantly between glass and plastics materials. For the latter, you must minimize deformation of the lens, which translates to using the lowest pressure that holds the lens securely in its fixture and against the lap during surfacing.

Abrading glass materials requires significantly higher working pressure - otherwise, not much happens. Here the limitation is likely to be breaking the lens.

[Pete Hanlin]

Abrading glass materials requires significantly higher working pressure - otherwise, not much happens. Here the limitation is likely to be breaking the lens.
You aren't kidding! My first gig in the world of ophthalmics was working in a lab where we processed a significant amount of glass. For a year or two, I tried messing around with Baume levels, etc., before I realized the real key to fining/polishing glass is PRESSURE!

My nightmare used to be a glass job with really high cylindrical power (there were always areas that just refused to polish out). Once I got a good handle on pressure, glass became the easiest material to process!

Naturally, about the time I got really adept at processing glass, I moved to a lab where we didn't process glass...


PS- That's a pretty good price for glass blanks, I think...

[harry a saake]

:D Pete, you just reminded me of an old trick we use to do at B&L, when we had a lens that would not quite polish out, usually in the center. We would take a thin piece of paper and cut out about a 1/2 inch square, put that under the pad in the center and polish away, it actually worked.