1 step poly, polishing pads

[specs2see]

we grind alot of steep curves, does anyone have experiance with the 1 step fining pads?
the pads we use now are 280 grit 1st fine, and find that we have to fine the lenses 2 to 3 times before the curve is correct and the "dimple" left from the generator is gone.
i know that the 1 step pads are 500 grit.
any ideas?
i have already changed the fining times and pressures. it helped but i need to speed up the process.

[HarryChiling]

How long has it been since you trued your blade or replaced it?

If you did that not too long ago and the blade is fairly new, try checking the usr manual to your generator, I have in the past changed some of the settings to cut a smoother surface when coming off the generator, so it will polish well, but keep in mind you may be decreasing the speed of polish and fining and increasing the speed of generating if you make a real drastic change. AND DON'T DO IT IF YOU DON'T KNOW WHAT YOU ARE DOING. If
I don't add that one in then some one else will good luck.

[shanbaum]

we grind alot of steep curves, does anyone have experiance with the 1 step fining pads?
the pads we use now are 280 grit 1st fine, and find that we have to fine the lenses 2 to 3 times before the curve is correct and the "dimple" left from the generator is gone.
i know that the 1 step pads are 500 grit.
any ideas?
i have already changed the fining times and pressures. it helped but i need to speed up the process.

The one-step pads are less aggressive than the first fine pads you're using, so it's hard to see how they could help "speed up the process."

It sounds like either 1) your generator is not working properly (which includes not being correctly calibrated); 2) your laps are not cut correctly; or 3) both.

[RT]

specs2see: If there's a dimple in the center of the lens that requires you "to fine the lenses 2 to 3 times" to remove it, your generator is WAY off calibration.

HarryChiling: If you're talking about an SGX, reducing the cutting parameters doesn't actually improve your ability to polish. Your polish performance is strictly of function of what the surface looks like after fining. The sole important factor is to make sure that your curves are accurate through proper calibration.

As you point out, you need to know what you're doing...I've seen dozens of cases where people change the parameters such that their lenses take longer to cut, their cutter life is reduced, and lens quality is actually worse.

[Jubilee]

What kind of generator are you using?

When was the last time it was calibrated?

Is this happening with all lens materials?

Certain type of lenses?

what type of lap?

What kind of cylinder machine?

Cassandra

[specs2see]

hi thanks all, i am using a, ok dont laugh. Optek profile.
optek claims that the dimple is normal. on "normal curves" this is not a problem.
the generator is in calibration, and the cutter in new.
this problem is only on the steep curves. the 1st fine i have now is 280 grit, which is what Optek supplies, i know that the 1 step pad starts off as a 500 grit from PSI.
and this problem is only in fining poly, hi index and plastic come out great.
the equipment is the Optek mini lab.

[HarryChiling]

HarryChiling: If you're talking about an SGX, reducing the cutting parameters doesn't actually improve your ability to polish. Your polish performance is strictly of function of what the surface looks like after fining. The sole important factor is to make sure that your curves are accurate through proper calibration.

As you point out, you need to know what you're doing...I've seen dozens of cases where people change the parameters such that their lenses take longer to cut, their cutter life is reduced, and lens quality is actually worse.

When I first took over the lab, they were having issues with the lenses deblocking and had the chuck torqued way off axis a few times. The settings on the generator were cutting way too aggressively (depth of cut was ridiculous) you could actually hear the motor struggleing to get through the material, rather than the lab tech finding out what was wrong she just barely used it and ordered everything finished from our lab, bills were $8000 on average a month higher than needed to be. Since I have made some changes it works flawlessly and the lenses are not falling off any longer. I changed cribbing on all materials to cut from back to front (or other way around will have to look at the written settings) this prevented the blade from actually yanking the lens from the chuck (it happens) and I changed the final depth of cut slightly to get rid of pitting problems. It is true that the lenses take longer too cut, but I am in a small one man lab so production is not my concern and I will let you know about the life of the blade when that point comes, but so far so good.

I would have to say that if the settings on the machine were the default then they are set for the wrong lab. I have had that problem in a few small labs I have worked in (optronics equipment not gerber). The person setting up the equipment sets the thing up like I need a lens to come out of the generator in 2 seconds. My needs are different than a larger production lab and so my settings need to be different to accomadate that. When I worked in a large lab we wold check our equipment sometimes twice a day for calibration (morning and after lunch). In my small lab I check it once a week and sometimes I will get lax (don't kill me shanbaum) once every two weeks. I don't run my machines all day at break neck speeds so they take less abuse. I have only had one problem in my lab since takeing over and I would like to thank shanbaum and his guys for helping with that (computer crashed, not innovations but it toke innovations down with it chalk that up to windows). I still haven't tried the settings change for cutting the convex cross curve (just procrastinateing), but have a feeling your suggestion will work.

[Jubilee]

steep in even in spherical corrections, or when there is a siginificant amount of cylinder?

[HarryChiling]

Is the pad thickness figured in and correct?

[DragonLensmanWV]

hi thanks all, i am using a, ok dont laugh. Optek profile.
optek claims that the dimple is normal. on "normal curves" this is not a problem.
the generator is in calibration, and the cutter in new.
this problem is only on the steep curves. the 1st fine i have now is 280 grit, which is what Optek supplies, i know that the 1 step pad starts off as a 500 grit from PSI.
and this problem is only in fining poly, hi index and plastic come out great.
the equipment is the Optek mini lab.

Well, your Optek is roughly equivalent to our Optronics Vista generator. If the Radius Bias (what it's called on the Optronics ) is too high, you will get a dimple in the center and your lenses will steepen towards the edge, If it's set too low, you get a hump in the center. and your lenses will flatten towards the edge. This is caused by the blade not being aligned properly with the geometric center of the chuck and lens.This can happen also if your blade is not vertically aligned, though that should be very rare,unless you've replaced your motor.
See if your Optek has something that fits that description and try adjusting it.
You might also try to set your curves oh-so-slightly flat so you'll fine the center first - not best but workable.

That said, I've never found a one-step pad that I trust, especially on steep curves.

[HarryChiling]

That said, I've never found a one-step pad that I trust, especially on steep curves.

Amen.