|Free-form generators, like Satisloh’s VFT-macro generator, use a single diamond point to lathe the lens, not grind it.|
|Topcon’s Model No. DS5000 blocker displays the correct lens blocking position to help eliminate unwanted prism errors.|
|ATTITUDE IS EVERYTHING Employees with low job satisfaction can negatively affect a company because they typically lack motivation, perform poorly, and possess negative attitudes. These attitudes can directly affect a company’s bottom line. Managers should understand the reasons employees are unhappy at work. Causes of dissatisfaction are: employees feel underpaid, limited career growth and advancement, a lack of interest, and poor management. Understanding the causes can help managers find the right solutions and reduce workplace errors, increase productivity, and job satisfaction.|
|Modern blockers like National Optronics’ 3BX help eliminate unwanted prism errors that can occur during the generation phase due to improper blocking.|
ECPs can achieve an error-free surfacing lab by following these five simple strategies.
As a seasoned surfacing technician, I can assure you that more often than not, surfacing problems can bring lens production to a screeching halt. Fortunately, most surfacing lab errors can be avoided if extra attention is given to a few basic maintenance procedures and preventive measures.
There are three fundamental types of errors that occur in the surfacing department:
- Power problems, which include axis errors
- Prism errors
- Defects such as generator marks, lens pitting, and physical aberrations such as waves.
Power problems are most often caused during the generation process when the curves generated onto the backside of a lens are incorrect. Axis issues can have several possible causes: for example, the lens could be blocked off-axis or the lens could be generated off-axis. Prismatic errors occur when a lens has unwanted prism ground into the lens during the generation phase. Additionally, prism can be unintentionally induced into a lens during the blocking process. Modern blockers like National Optronics’ 3BX and Optek’s Topcon Model No. DS5000 help eliminate unwanted prism errors.
Defects are usually produced during the fining/polishing stage. Heat buildup can cause lenses to warp slightly, causing waves. Waves can also be caused by not enough water or polish hitting the lens surface. Additionally, too much pressure on the pin clamps can cause waving. Generator marks are a common occurrence. Usually these are produced because the generator isn’t calibrated properly: wrong laps are being used on the cylinder machines, or the fining pads did not remove enough lens material. Pitting is caused during the generation process and is due to defects on the generator’s cutting wheel or bit. Free-form generators, like the VFT-macro generator from Satisloh, avoid all these issues since they use a single diamond point to lathe the lens, not grind it.
Although there are additional surfacing lab errors that do occur, these are the most common and most likely examples. But there’s good news! These errors can be avoided. By following these five simple strategies, you can dramatically improve the surfacing department’s overall output and your bottom line.
1. KEEP IT CLEAN
Maintaining a clean work area (this includes equipment) is arguably the simplest task on this list. It’s also one of the most often neglected tasks. This includes a daily wipe down of machinery to remove any splashed polish or particle buildup. Lens rinsing trays should be periodically rinsed, wiped out, and refilled with clean cold water. Keep slurry traps clean and particle free. A thorough cleaning of cylinder machines should be done weekly, including changing out old polish. Lens polish can be a particularly caustic agent and should be removed from any small equipment such as lens de-blockers. If you use a turntable-type lens washer, it’s important to occasionally clean the brushes to remove any fine debris that could potentially scratch a lens. Blocker rings and blocks should be regularly cleaned to remove any blocking medium fragments or polish buildup that could cause prism during blocking. Keeping the surfacing area and machinery clean significantly reduces lens breakage and spoilage.
2. PERFORM SCHEDULED MAINTENANCE
Daily and periodic maintenance is essential for keeping machinery and equipment in good working order. Follow all manufacturers’ suggested maintenance schedules and procedures. Make sure to keep machines that require lubrication, such as cylinder machines, fully greased. (Cylinder machines require occasional belt timing to ensure proper table stroke.) Periodically inspect for loose nuts, bolts, and connectors. Check air lines and connectors for cracks or leaks. Verify air pressure settings on the pin arms. Thoroughly inspect all baffles for tears, rips, or holes and replace if needed. Often overlooked maintenance duties include checking pin clamp pins for excessive wear and table axes. Make sure to be thorough and adjust, fix, or replace if necessary.
3. TREAT EVERY JOB AS A PRIORITY
Prescription possibilities are unlimited, so in effect, every job is a distinctive combination of a complex set of variables. That means every job should be treated as unique. Some jobs of the same material, for example, may need a little more or a little less fining time. High minus lenses may leave center dots more easily than plus lenses due to the way they sit on the lap and because the edge thickness makes it difficult to get water/polish onto the pads. Therefore, extra attention is needed to ensure a defect-free finished surface. Lenses should be thoroughly inspected for defects between the fining and polishing processes. To remove generator marks and pits, it’s sometimes necessary to run the job a little longer, change pads, or both. Above all, avoid treating the surfacing process as an assembly-line procedure.
4. KEEP IT COOL
Surfacing processes that require coolant need to retain proper coolant temperatures to operate efficiently. Equipment that’s not operated at the proper temperature can cause waves, distortion, and other forms of visual aberrations, not to mention excessive wear on the equipment.
5. CHECK YOUR CURVES (CALIBRATION)
It’s important to always keep your lab machinery calibrated. As the generator is the heart of the surfacing lab, it is paramount to its proper functioning to keep it properly calibrated. The generator should be checked regularly for curve and thickness accuracy. This will not take more than a few minutes and will protect against a day of bad lenses.
Depending on the size of your workload, it may not be necessary to adhere to all of the above suggestions, word for word. For example, if you surface only 25 jobs a week, it may not be prudent to change out your polish on a weekly basis. Nevertheless, using these recommendations as general guidelines for your practice will reduce overall surfacing lab errors and keep your lab in top running order.
Steven Warfield is a lab technician and freelance writer based in Harrisburg, PA.
|BASIC ERROR DIAGNOSIS The following is a basic diagnostic guide to common surfacing errors, what is most likely to produce these errors, and the method to remedy the problem.
ERROR: Power is off, too much or unwanted cylinder, the lens is off-axis.
ERROR: Lens has waves or other physical aberrations.
ERROR: Unwanted prism.
ERROR: Surface defects.
WHERE TO FIND IT:
800-866-5640 • nationaloptronics.com
Satisloh North America
800-866-5640 • satisloh.com
727-522-2301 • optekinternational.com