Does anybody have any trick on fining and polishishing polycarb lenses?
My staffs, they are spending 30 minutes to 1 1/2 hrs.(or more) in fining and polishing the poly lenses. It sure takes forever to remove those stubborn swirls. I don't know what we are doing wrong. It's a nightmare everytime we see a semi-poly job. I am thinking of calling Gary at PSI to see if he can give me something better. Does anybody have any trick in fining and polishing poly lenses?
Don't use poly.
+1Originally Posted by chip anderson
It sure takes forever to remove those stubborn swirls.
I can help with above lettle problem. Srape off swirls with a knife and use Polycarbonate Edge Polish, wipe it over the edge and you have a beautiful edge finish.
It works on poly like acetone used to work on the old zyl frames. Easy Job !!!!!
http://optochemicals.com/products/in...dge_polish.htm
Depends on what kind of fining and polishing pads you are using. Also what is the pressure setting for your cylinder machines. It only takes me about 10 minutes to fine and polish poly lenses.
Yep. How long is it taking you to produce a pair of CR39 ?
Chris Beard
The State of Jefferson !
I'm a Medford man – Medford, Oregon. Up in Medford, we take our time making up our minds."
Call Gary at PSI...he's great.
RT
To fine and polish CR-39 takes about 7 minutes.
Wow.
Poly with PSI one-step fining pads and standard polish pads should be just under 8 minutes.
CR39 with PSI one-step fining pads and standard polish pads should be just under 6 minutes.
Beyond the types of pads and machine pressure, check axis, check if the pins are nicely pointed (rounded over they should be changed), and check the arm throw and stroke to ensure equal movement (top to bottom, left to right) along the lap tool.
with swirls you have to start from the bottom as Audiyoda said. Most times we start getting swirls because our pins on the cyl machine are blunting but at the same time you have to check the inserts on the block are not worn.
If you are cutting laps are they calibrated?
Wow those times are ridiculous. Even an amateur like me can get poly fined within 5 min and polished in another 5 or 6. It could be a dozen things. Have you checked your blade radius calibration? Do a 7 second test...i.e. mark the back of a lens to be fined with a spoke pattern using a china marker. Run the finer for 7 seconds. Take the lens off and see if the marks are wearing off evenly. Are you using rough pads?
I agree that PSI will help you troubleshoot.
We were having problems recently. Turned out all I had to do was flatten the curves on my generator by .03D. I was fining from the inside out,and that worked well for everything except poly. I had too much pad loading in the center.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
Gotta get the right pads and slurry if ya wanna fine poly! Cylinder machines are one of the easiest machines to calibrate and get working properly. Also, like Dragon says, check the generator to see what's going on there. Alot of problems with fining and polishing are rectified by getting the generator cutting smoothly.
As others have said... that is WAY too long.
Check gen.
Check if you are using correct pads/times/pressure.
Can you please list the equiptment you are using to process poly we have an sl-2, optek 425's using one step pad system... Poly tmes..2 minutes to fine 5 minutes to polish. Great results regardless of curvature
Who's one step if you don't mind me askin'. We've been unable to use one step on poly. Our generator (Optek Profile SL) leaves a dimple at the center and so we have to fine longer and harder. Even with two step we need 4 minutes rough and 1 minute fine. We use PSI pads. We also use Optek 425s.
Dac pdr6050nc velocity poly pad with pdr0700n lumina polish pad. Keep in mind curves off gen must match lap..calibration is key! Check with optek on calibration..as mentioned in this thread..smooth cutting gen makes all the difference
There should not be a dimple at the center left by the generator. That is a Radius Bias correction on my Vista generator. The chuck and the blade do not agree exactly on where their common zero point is.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
I have the calibration tool for this alignment check and have done it. The results indicate perfect alignment. What you say makes sense though. I will try it again.
Would a dimple mean that I would have to go flatter or steeper on the radius correction?
I have been told though, that a dimple in poly is not uncommon in older generators, and that in newer ones, the generator software will pull the blade back a fraction as it approaches the OC to create a slight pimple (not dimple), as it is easier to fine a pimple than a dimple. (I can't believe I just said that). Have you heard of this?
Do you have a minus curve SAG gauge? You need to check the curve at the center of the lens and also at the periphery. If your bias is off, they won't quite be the same. Adjust it until the curve is the same centrally and peripherally. That should eliminate your dimple.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
My generator doesn't allow changing curve differently from center to periphery...but I am surmising that it might be easier to fine out a poly dimple if the generator curve is slightly flatter than the tool curve. Would you agree?
Fining Problems.
These can come from several locations. As stated before I would first backtrack to the generator. It could be cutting off axis or wrong curves all together. A way to tell if its an axis issue the swirls will be on opposite corners of the lens as it fines down and spherical lenses wil have no problems. I would cut a lens with a 4D cylinder or so and clamp it down on your cylinder machine and look to see if lens is flush with lap. (Assuming of course the cylinder has already been found to be on axis itself) Also I would cut a plano lens and fine it for 30s or so and check fine pattern. (you can use this lens to check for generator prism as well) If fining is not even, for example lens is fining outer edge first generator is cutting too steep. If it is fining center out generator is cutting too flat. (This assumes you have good laps)
Once Generator is eliminated its time for cylinder machines. Some of this has been stated in prior posts. First check everything you can on cylinder before actually placing a lens on it. Axis, with the alignment block, PSI ( I run 18 but I have seen more or less work you just have to adjust your fining times accordingly), stroke pattern and centering (this is rarely out of alignment but worth checking), good chilled coolant flow, and Fining pads (I have seen people try to use plastic pads for poly not knowing they are different).
I would do both of these simultaniously. Don’t just check your generator, find a problem then stop there. Checking all of this shouldn’t take more than a few hours.
Now for cylinder setup
When setting up a cylinder machine you need to decide what fining pads you are going to use. Once generated deblock the lens and check thickness then reblock it. Fine the lens. It has been my experience that poly should not take longer than 2m to fine in no matter the power. (4m if 2 step) Now deblock the lens again (If using 2step don’t deblock until after second fine) . Now check center again. You now know how much material is being taking off in the fining process and can adjust your machinery accordingly. My minus (non drillmount) poly comes out at a 1.2 CT everytime no matter the power.
As to the dimple. I am not that familiar with Optek generators but I had that problem on a SGX once. It was only on Trivex and Poly lenses. Turned out it was a combination of wrong fluted blade and spindle speed. We were building up too much heat and the dimple was melted lens leftover from the last blade pass.
Hope this helps
Interesting thought on how the dimple forms. I will see if I can adjust my finish pass to be less aggressive, and see if I can keep it cooler. Thanks.
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