Our back curves/cross curves are coming off our generator accurate but after fining we are 0.50-0.75D too flat (under minus). We checked the laps and the sags are fine. The pressure is set between ~12-14. We use alloy to block. Ideas? Advice?
Our back curves/cross curves are coming off our generator accurate but after fining we are 0.50-0.75D too flat (under minus). We checked the laps and the sags are fine. The pressure is set between ~12-14. We use alloy to block. Ideas? Advice?
Doc:Originally Posted by DocInChina
I've been trying to figure this out since I received your PM. The only thing I can think of right now are bad lenses (maybe a bad batch).
It makes no sense to me.
Are you tools compensated?
Have you checked the front surface radius of the lens?
Have the blancs the right index?
Are you calculating with the same tool index as the tools are made?
What kind of generators?
What kind of smoothing/polishing machines? Stroke checked?
This particular setup is our backup system (manual generator). The tools are compensated and we ran the numbers with software as well as with a calculator to verify. All our laps are made to index so we use 1.498 tools for 1.498 index lenses.
The curves coming off the generator are dead on. The polishing machines are domestic for the backup system. I am not sure how to check the stroke.
Makes no sense to me either. The lenses are chilled for about 15-20 minutes after blocking and since the weather dropped the past few days anyway I do not think the alloy is having trouble cooling fast.
The lenses were checked prior to running so I know the front curves are right. We clock the lenses off the generator and the curves are correct. Very frustrating.
Can you generate a -6.00 dpt curve index 1.498. Diameter 65 or 70mm.
Then run this on you +6.00 dpt index 1.498 tool for 5 sec.
If it beginning extremly from edge eighter you generetor must be to steep.
But you said you have controled this and it was acurate.
Or you tool is to flat.
The stroke cant make the differece you told, the same with alloy.
Thats what I plan to do first thing..run center block sphere curves and then fine them and see what happens. I will update you if I make any headway.
Thanks for your input.
What are you using to check the curves and laps, because these devices are usually calibrated in 1.53 index and the difference in low curves can be a 0.25 D.
We convert the index curve to match the instruments index reference.
Going down to factory floor now. Will update later.
Are you fining from the center out or the edge in. The latter is correct. Same with polishing.
As one of my mentors used to say, "Well ground is half polished". Ideally, if you've ground the lens correctly, you will neither fine edge in nor center out. You will fine evenly across the whole lens. That's the major concept behind computerized generators.Are you fining from the center out or the edge in. The latter is correct. Same with polishing.
RT
Well......I am just throwing other stuff out there. It has been so long since I tickled the Coburn Rockets, that I don't have a clue!
1.) Heat?
2.) Bearings wearing out?
3.) Timers off?
Eric, do you have too much pressure??
You means fining ain't done with finin emery anymore? Just before soothing with smoothing emery? Before polishing? Lawsy me, the world done changed again.
Chip
Yes, thanks for asking. ;)
Regarding the finer/polisher the pressure is not high. We think we found the problem and testing now.
Eric
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