# Optical Forums > Ophthalmic Optics >  surfacing - question for lab managers

## essegn

We use the conventional production line from SATISLOH (generator + smoothing and polishing machine).

Our daily production is about 250 lenses per day.

We have power off errors at high index material about 20%. We do the high index material on 0.12 dpt step flat back tools.

I know that to achieve more efficient production in power off errors is to produce it on more exact flat back tools steps (0.06 or 0.03).

Due to low volume of production it has no sense (because of price and place for storage) to create the additional flat back tools (like 0.06 or 0.03) so i would like to know the following:

Does anybody have any ideas how to figure out this situation ?

I found out one company that procudes exact flat back tool from teflon and by the all high index materials they will cut the exact tool. In middle europe i was not able to find the cheap teflon material.

My imagination about price for 1 piece of any material that we will produce from it the exact curve is maximum 2 Eur per piece.

I checked the flat back tools at few comapnies and the lowest price for tools is 5 Euros.

Thank you in advance!

Peter

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## HarryChiling

> We use the conventional production line from SATISLOH (generator + smoothing and polishing machine).
> 
> Our daily production is about 250 lenses per day.
> 
> We have power off errors at high index material about 20%. We do the high index material on 0.12 dpt step flat back tools.
> 
> I know that to achieve more efficient production in power off errors is to produce it on more exact flat back tools steps (0.06 or 0.03).
> 
> Due to low volume of production it has no sense (because of price and place for storage) to create the additional flat back tools (like 0.06 or 0.03) so i would like to know the following:
> ...


This may be too simple of a fix, but what is the index of your tools?  Are you compensating the tools for index?

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## WFruit

If you haven't already, make sure all the lens data (true front curve, sag, etc.) in your lab software is accurate. Manufacturers will sometimes change their lenses without letting anyone know.

I'm curious to know if you see errors more with any particualr index (1.60, 1.67, 1.74, etc.) or if there's any more/fewer errors on spheric vs. aspheric.

And Harry is, of course, correct to check the tooling index as well.  And of course, check to make sure the curves on the tools themselves are accurate.

We're also running Satis Loh (gods help us) although all of our curves are cut to .10 on the conventional generators, and .01 on the Digital generator.

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## HarryChiling

> If you haven't already, make sure all the lens data (true front curve, sag, etc.) in your lab software is accurate. Manufacturers will sometimes change their lenses without letting anyone know.


It is always a good idea to sag your lenses before surfacing, you'll find that in many cases this can help to resolve power issues and catch warped lenses before precious time and resources are wasted.  A digital sag gauge is a must, also make sure to caliper your lenses as thickness is always off from the average lens manufacturers data this will prolong your cutters life as you won't have the tool crash into a lens that is thicker than expected.

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## essegn

thanks guys..

used tooling index is 1.498. On the conventional SATISLOH line use the only aspherical semi finished materials and we have more power off errors at 1.6 like higher indexes. 

I'm sure that some of the base curves have to be adjusted, but i would like to know the how good results could we achieve if we produce the high index material on tooling index 1.498 in 0.12 steps.

WFriut  - do you use the same tooling index and all the lenses are in 0.1 tolerance? 

What is your power off breakage at high index materials ?

We have the digital SAG meter from Coburn, but i really dont know how to measure with that device because if i measure the same curve more time i will always get different values. The difference is not so much, but i has quite big influence on final diopters. I figured out the best way to produce it and see how the result diopter looks like.

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## essegn

Could somebody explain to me for what is tooling index good for ? For me, it is obvious that for 1.498 material is good tooling index 1.498 and for 1.6 material is 1.6 tooling index.

If we use tooling index 1.498 for all material indexes what does it mean? Is there any possibility to change the tooling index for higher one? If so, what does it mean in real? The new flat back tools?

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## WFruit

> Could somebody explain to me for what is tooling index good for ? For me, it is obvious that for 1.498 material is good tooling index 1.498 and for 1.6 material is 1.6 tooling index.
> 
> If we use tooling index 1.498 for all material indexes what does it mean? Is there any possibility to change the tooling index for higher one? If so, what does it mean in real? The new flat back tools?


The simplest solution is to tell your lab software what your tooling index is and it will compensate it's curve calculations for whatever the lens index is.

For example, all of our tools are cut in .10 diopter increments, 1.498 tooling index. We use the same tools for all materials, all indexes. Our lab software knows what the tooling index is and compensates its curve calculations based on that. Our off power breakage accross all indexes is very, very low. We usually only run into issues when a vendor changes the true front curve and doesn't bother to inform anyone.

See here for an article on tooling index: http://books.google.com/books?id=Zl4...page&q&f=false

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## Wes

Oh my. This is going to take a lot more explaining than I'm willing to do on a blackberry. If no one beats me to it, I'll write out an explanation of tooling indices for you when I get home.

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## Wes

Hey cool, you beat me to it.

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## essegn

> For example, all of our tools are cut in .10 diopter increments, 1.498 tooling index. We use the same tools for all materials, all indexes. Our lab software knows what the tooling index is and compensates its curve calculations based on that. Our off power breakage accross all indexes is very, very low. We usually only run into issues when a vendor changes the true front curve and doesn't bother to inform anyone.
> 
> [/URL]


we use 0.125 step tools.. What is difference between yours tools and ours? the only 0.025 diopter difference ?
I would like to know which accuracy we can achieve with 0.125 step tools.

I have one more question: If i set aspherical semifinished material to rX program like spherical semifinished material (if i ignore the aspherical topografy and the only radius is set), does it have influence on final power in the optical centre (in our case geometrical centre) or it will only cause the worse peripheral vision?

How do you measure the front curve? By sag meter and then you will shift the front curve according to result ?

What is your internal tolerance for tools? For example toll has to be -8.53. What is the bigest acceptated tollerance? Or it has to be the exact -8.53?

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## HarryChiling

Well here goes a simple explanation if your using lets say a 1.67 lens blank and tooling in 1.498 (0.12 steps) as an example:

Rx: -4.00 sph

Using the simplified lensmakers equation and assuming you need to use a 3.00 base lens:

The front curve is often given as a TBC (True Base Curve) which is referenced to a index of 1.53, so if you measure it with a lens clock it will read what's on the box. The base curve given in the materials index is:

D(material) = (0.67/0.53)*3.00 = 1.26

Ignoring the thickness the back curve power would be:

Back Curve = 1.26 - (-4.00) = 5.26

So the back curve you need is a 5.26, but we're not done yet, the back curve needs to be computed into the tool index that you will be using:

Tool Curve = (0.498/0.67)*5.26 = 3.91, the closet tool you'll have to that is the 3.87 so that would be the proper tool to use. 

If your software has 1.53 as the tool index then back surve would be calculated to:

Tool Curve = (0.53/0.67)*5.26 = 4.16, the closet tool would be a 4.12, so you can see where there is a disparity. 

Your software like mentioned should allow for you to input the tool curve, you should have this set to the 1.498 value since thsoe are the tools you have available. Also make sure you have pad thicknesses compensated for in the software or on the tool. If your using aspheric lenses it won't matter what the aspheric value is if the lens has a sag value on the box since that sag value should correspond to the same sag value of the lens, however that sag value is used for calculating thickness not power, the TBC is going to be used for the calculation of power.

The best suggestion is to have an experienced lab man look at your set up and program the values accordingly. Also since your tool index is in 1.498 and the most common or default tool would be in 1.53 that may be where you issue is. In th case of lower index lenses you are putting lower powers in the lenses and the material index is closer to the 1.53 so the error might not be as evident, however in higher indices you will have a larger disparity and higher powers so you'll see a bigger error. Without really seeing your set-up it's hard to diagnose or guess at what the problem might be, but it is definately worth checking into.

Sorry beat you to it Wes, although I am notorious for getting th emath wrong so the example may have a kink in it's armor. ;)

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## WFruit

Oh thank goodness I don't have to explain it.  :p

It turns out that I did remember it right, but with lab software being what it is today, so much of the math is taken care of by the computer.  All you have to do is make sure the software has the correct values and it takes care of the rest.  

To answer one question, using tools cut in 0.125 dipoters, you should expect to cut lenses that are accurate to 0.125 diopters of what you need. As you can see in the example above, the actual calculations are down to 0.01 diopters, and then you round to the nearest available tool.  The smaller the increments your tools are cut to, the more accurate you can cut your lenses, due to the value of the tool being closer to need needed back curve.  However, most labs, when processing lenses on conventional equipment (as opposed to digital surfacing) use tools that are cut in 0.125 increments (some will use  0.10 increments, like we do, and I've even seen a few in 0.0625.  And some insane, and usually smaller labs, will cut tools individually for each job accurate to within 0.01).

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## HarryChiling

> And some insane, and usually smaller labs, will cut tools individually for each job accurate to within 0.01


Not really insane for a small lab, cutting tools on foam can save the space required for keeping tool racks full of tools and it increases accuracy.  Sure it costs a little more but for small in office labs I actually loved not having to pull tools for every job and since in most small labs high production isn't an issue the extra time needed to cut the tools was not a big deal.  If you were to try that in a large production lab then that would be insane since the generator would be running inefficiently by wasteing time, to put the tool in, to cut the tool, and then to take the tool out.  These things add up.  

I would personally advocate any small operation to use foam laps as the convienience will far outweight the costs.  I know a few small labs that have a small raneg of tools and anything outside of that they use the foam tools to make this is a great set up as well.  I would always mark my foam laps as well for how many cuts I had in them and when your jobs are arranged properly you could get 3 sometimes 4 tools from one foam block.

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## essegn

> Not really insane for a small lab, cutting tools on foam can save the space required for keeping tool racks full of tools and it increases accuracy.  Sure it costs a little more but for small in office labs I actually loved not having to pull tools for every job and since in most small labs high production isn't an issue the extra time needed to cut the tools was not a big deal.  
> 
> I would personally advocate any small operation to use foam laps as the convienience will far outweight the costs.  I know a few small labs that have a small raneg of tools and anything outside of that they use the foam tools to make this is a great set up as well.  I would always mark my foam laps as well for how many cuts I had in them and when your jobs are arranged properly you could get 3 sometimes 4 tools from one foam block.


Exactly as you wrote.. Due to low production value we have a time to produce the exact tools on each high index order.

Do you know any producer of foam tools you can recommend me? Because i have heard that foam tools are not good, because the material tends to heat up during smoothing and polishing operation which causes distortion on the final lenses.

How to work with foam tools that we are intend for making the exact tools? As you wrote that you are able to cut 3-4 exact tools. For example, if you need the tool of -5,00 and then you will need the tool of -10,00;-6.00. So in this case you are not able to do that on one foam tool.

What is the more efficient way how to decide how many foam tools to have in order to be able to produce 3-4 tools from one foam tool?

I have one more question: We have an analog SAG meter as well. So if i measure the SAG height of semi finished 1.68 it has to be recalculated to the radius (and then to TBC) with index 1.53 ?? and than the TBC from 1.53 index to 1.498 for CR39 ??

I do not understand why the SAG height is good the only for thickness calculation. I have been taught that you measure the SAG height. In case that you measure the CR39, you will calculate the radius (for example: SAG 1,68 ; material index=1.498) and then if you have radius calculated, you will calculate the real diopter of front curve.

Is it correct method ?

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## essegn

> Rx: -4.00 sph
> 
> Using the simplified lensmakers equation and assuming you need to use a 3.00 base lens:
> 
> The front curve is often given as a TBC (True Base Curve) which is referenced to a index of 1.53, so if you measure it with a lens clock it will read what's on the box. The base curve given in the materials index is:
> 
> D(material) = (0.67/0.53)*3.00 = 1.26


  Is that correct _?

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## shanbaum

While it is common for lenses to be marked with 1.53 curves in the U.S., that is not the rule in the rest of the world, where they are usually marked in material diopters.  Similarly, while 1.53 laps have been the rule in the U.S. until recently, in most of the ROW, laps have been index-specific.  That's changing due to the proliferation of indices; labs are using laps cut in higher indices and/or smaller increments - either of which increase the "resolution" of the lap set.  I've always been a proponent of material-index-specific laps, although the new conformable-lap systems obviate the issue altogether.

While some lenses are marked with sag values, these are usually just conversions from dioptric curves to sags at 50mm; they can be used for power calculations, when the calculator requires a sag to be input, but are not useful for thickness calculations on aspheric lenses.

Harry's calculation was incorrect;  0.67/0.53 = 1.26; multiply that times 3.00 and you get 3.79 - which means, a curve specified as 3.00 diopters in a 1.53 index has an actual surface power of 3.79 if the material index is 1.67.  However, it's likely that in your location, you needn't concern yourself with that 1.53 index at all.

Using 1.498 laps cut in increments of 0.125 for higher index materials is going to be problematic.  While your software can find the closest lap in the set to the curves required, it can't change the laps - the increments are what they are.  On 1.67 materials, the intervals between your 1.498 laps cut in 0.12D are 0.17D.  Given that your laps are not going to be exact (if they're within 0.02D, you're doing well), it's easy to see where your lap errors alone can be 0.10D.  That's before anything else goes wrong.

I recall there having been a fairly extensive discussion on this topic here on Optiboard a number of years ago, but I haven't been able to find it yet.  I wish I could; I think we beat the subject to death and maybe then some.

Harry's right about foam laps - they're a great solution for a low-volume lab that processes a wide variety of materials.  They do have to be used carefully.  So far as I know, they're only available from Gerber.

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## Speed

> It is always a good idea to sag your lenses before surfacing, you'll find that in many cases this can help to resolve power issues and catch warped lenses before precious time and resources are wasted. A digital sag gauge is a must, also make sure to caliper your lenses as thickness is always off from the average lens manufacturers data this will prolong your cutters life as you won't have the tool crash into a lens that is thicker than expected.


 Not always.

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## essegn

> While some lenses are marked with sag values, these are usually just conversions from dioptric curves to sags at 50mm; they can be used for power calculations, when the calculator requires a sag to be input, but are not useful for thickness calculations on aspheric lenses.


 I am confused a bit.. if i found the SAG number at 50 mm on the 1.67 blank. Should it be recalculated to true base curve with 1.53 index or 1.67 index?
not useful for thickness calculations ? i am not sure, but if you have front curve in diopters (calculated from SAG) and according to set thickness, rX program calculates the final diopter. Could you please explain it to me ?





> Using 1.498 laps cut in increments of 0.125 for higher index materials is going to be problematic.  While your software can find the closest lap in the set to the curves required, it can't change the laps - the increments are what they are.  On 1.67 materials, the intervals between your 1.498 laps cut in 0.12D are 0.17D.  Given that your laps are not going to be exact (if they're within 0.02D, you're doing well), it's easy to see where your lap errors alone can be 0.10D.  That's before anything else goes wrong.


Sorry, but i dont understand.. why the interval  between 0.12D tools is 0.17D ? why not 0.12 ?
what does it mean that lap errors alone can be 0.10D ?

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## Speed

> I am confused a bit.. if i found the SAG number at 50 mm on the 1.67 blank. Should it be recalculated to true base curve with 1.53 index or 1.67 index?
> not useful for thickness calculations ? i am not sure, but if you have front curve in diopters (calculated from SAG) and according to set thickness, rX program calculates the final diopter. Could you please explain it to me ?
> 
> 
> 
> 
> Sorry, but i dont understand.. why the interval between 0.12D tools is 0.17D ? why not 0.12 ?
> what does it mean that lap errors alone can be 0.10D ?


Many high index lenese are aspheric.  Do not sag an aspheric lens. Get the published true curve from the manufacturer for power calculations.

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## Darryl Meister

As the others have pointed out, your lap tools will definitely be an issue. This may or may not be your only issue though. You really need to investigate the issue further in order to understand the potential sources of your off-power errors, especially since the problem seems to occur more frequently in higher index materials (I have a paper that discusses some of the issues associated with refractive available for download from OptiCampus.com).

A few questions to consider:

1. Are the power errors relatively systematic or random? Are the errors biased toward plus or minus powers? Errors due to your tooling increments should be fairly random, for instance.
2. Does it occur with specific lens suppliers, lens designs, or lens materials more frequently than others? Have you verified that your software has the most recent lens specification data from the lens supplier? Do they only occur in high-index materials or do they actually occur in high powers, which are often more commonly produced in high-index materials?
3. If you're using an automatic focimeter, is your device calibrated to the correct reference wavelength and the correct refractive index of the lens material? Have you compared the results of multiple devices?
4. Is pad thickness a potential issue if you are using different fining pads for high-index materials? What about stock removal rates?
5. Have you noticed any blocking, generating, or fining waves on the lens surface after surfacing?
6. Have you verified the calibration of your equipment and lap tools, using something like a lap tool gauge?

Etcetera. Some of the other lab guys could probably provide some other tips and potential problem areas to consider.




> I am confused a bit.. if i found the SAG number at 50 mm on the 1.67 blank. Should it be recalculated to true base curve with 1.53 index or 1.67 index?


Does your surfacing software accept a sag value? If so, the software should perform the necessary conversion for you.




> not useful for thickness calculations ? i am not sure, but if you have front curve in diopters (calculated from SAG) and according to set thickness, rX program calculates the final diopter. Could you please explain it to me ?


The "sag" value or true curve supplied with aspheric and progressive lenses is not the actual physical height of the lens blank over a given diameter. It is only describes the "theoretical" curvature of an equivalent spherical surface over a very small region of the distance zone that is used to calculate the surface power of the lens blank over this region.

An aspheric front curve, for instance, may be steeper or flatter than the theoretical base curve specified by the lens manufacturer for power calculations. The actual, physical height of the lens blank over a given diameter, which is necessary for thickness calculations, may vary significantly from the sag value specified for power calculations.




> Sorry, but i dont understand.. why the interval between 0.12D tools is 0.17D ? why not 0.12 ?
> what does it mean that lap errors alone can be 0.10D ?


If your lap tools have been calibrated to a refractive index of 1.498, the interval between each tool is also based on this index. If your lap tools are marked in 0.12 D increments, this increment only applies if the material has the same refractive index.

If the index of the actual material is higher, the difference in curvature between your lap tools results in a greater difference in actual surface power. For a 1.66 lens material, lap tools marked in increments of 0.12 D in an assumed index of 1.498 produce an actual difference in surface power of (1.66-1)/(1.498-1)*0.125 = 0.166 D. Since your potential rounding error is half of this value, your lens powers will be off as much +/-0.08 D, just from your lap tools.

This is actually one advantage to a system based on the US tooling index of 1.530 or any higher refractive index, since it results in more lap tools, as Robert noted. Basing lap tools on the refractive index of the actual material is a good idea as well, since you could stock the cylinder powers in only 0.25 D steps, significantly reducing your lap tool inventory for cylinder powers. But this would obviously require multiple lap tool sets, which is apparently impractical in your situation.

Given your investment in 1.498 tooling, however, I suspect that the easiest short-term solution for increasing the accuracy of your lap tools would be to fill in some of your lap tools with a few 1.498-index tools in 0.06 D increments, focusing first on the prescription ranges that most frequently result in off-power errors for you. This will obviously cut your potential rounding errors in half.

Best regards,
Darryl

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## HarryChiling

> While it is common for lenses to be marked with 1.53 curves in the U.S., that is not the rule in the rest of the world, where they are usually marked in material diopters. Similarly, while 1.53 laps have been the rule in the U.S. until recently, in most of the ROW, laps have been index-specific. 
> 
> I didn't know that, you learn something new every day.
> 
> While some lenses are marked with sag values, these are usually just conversions from dioptric curves to sags at 50mm; they can be used for power calculations, when the calculator requires a sag to be input, but are not useful for thickness calculations on aspheric lenses.
> 
> I had it flip flopped but yes they work i one sense but not in another, wow 1 year away from a lab and the information goes quickly.
> 
> Harry's calculation was incorrect; 0.67/0.53 = 1.26; multiply that times 3.00 and you get 3.79 - which means, a curve specified as 3.00 diopters in a 1.53 index has an actual surface power of 3.79 if the material index is 1.67. However, it's likely that in your location, you needn't concern yourself with that 1.53 index at all.
> ...


Great post.




> How to work with foam tools that we are intend for making the exact tools? As you wrote that you are able to cut 3-4 exact tools. For example, if you need the tool of -5,00 and then you will need the tool of -10,00;-6.00. So in this case you are not able to do that on one foam tool.


Do it in order:

5.00
6.00
10.00

Flatter to steeper, mark the tools with a grease pencil across the center, you want to remove stock on each new tool you make so if the grease marks are visible you should take the tool down another 1/2mm to 1mm.  They also make harder plastic laps which can be used multiple times, we used to use those for common powers in another lab I worked and when you ground the lap down to thin you would mark the power's on the side and place it in inventory with no further cutting.  The harder plastic laps had to be checked for accuracy more often but they still offered a permanent solution rather than a foam disposable solution.

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## shanbaum

Here's the thread I mentioned:

http://www.optiboard.com/forums/showthread.php/7157

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## Darryl Meister

> Great post


Yeah, I'm going to start calling Robert "The Tool Master." ;)

Best regards,
Darryl

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## shanbaum

Of course, you will not be the first...

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## Darryl Meister

> Of course, you will not be the first


LOL. I think I'm referring to a slightly different context than Mrs. Shanbaum was, Robert. :bbg:

Best regards,
Darryl

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## Jeff Trail

One other possibility to mention and I saw it no where in the post, but would you be possibly using an MR3 coater or mini? I went into a lab about a month ago and they were having tons of issues..first told me power and than when they sent me some samples I was locating tons of aberrations off center... called and asked them to check powers coming right off the line BEFORE coating.. and tada..it was the backside coater...had them dip the lens in  heated distilled water in the tint unit and the "power problem" was solved....
    If it is a "lap" issue you should be seeing a pattern to the lens powers vs.. index ... if you did than you could always just run a compensation chart to set you cross/base and tools or just let the compensated tool bring it in...more chance of swirls/waves if you do not compensate both cut and tool though.. sometimes spending a lot to solve a little can be corrected with a "free" work around..
    Poor guys answer to buying laps in 6ths..or even 10ths...
  Just a thought of something I did not see mentioned.....

Jeff T.

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## Darryl Meister

Our Prodigal Son has returned! What's it been, Jeff, a year or two?!?

Best regards,
Darryl

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## shanbaum

I thought we were doing the Time Warp again...

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## HarryChiling

Robert "The Too Master" Shanbaum, heck it beats being called a "tool".

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## Jeff Trail

tool? been called worse.. and truthfully probably lived up to the label  :Rolleyes:  ... 

Darryl, I still read postings about every day but it has gotten was to political and cut throat on here at times to make it worth while to reply, our old debates between all of us, even when political had a little more restraint and a bit of respect, agree to disagree type posts, even the optical postings have gotten a little more down and dirty and insulting...big difference in my book between being passionate vs.. condescending  ... I think I'll start tinkering in the ophthalmic section... leave the rest to the guys still full of spit and vinegar..:shiner:

Jeff "grind'em if ya got'em" Trail

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## Darryl Meister

Jeff, We generally get a little classier clientele in this particular forum. I mean, for people who drink cheap beer, anyway.

Best regards,
Darryl

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## JRS

Greeting Jeff. Been awhile and I hear ya.

Take care

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## essegn

> Here's the thread I mentioned:
> 
> http://www.optiboard.com/forums/showthread.php/7157


thanks for the thread.. Frankly, i didn't cath a lot, because of my english and ability to not understand it well :(

Thank you for your posts, it help me a lot, but in some topics i am somehow in the dark so I have a few questions that i would like to know:

1. We use the tooling index 1.498, tool step 0.125
    therefore, the strange thing for me is, that this tool step is only for CR39.

I try to explain it on example:

TOOL STEP for 1.5 index material                 TOOL STEP for 1.6 index material
  SPH                CYL                                        SPH           CYL
 -4.00                0                                         -4.00            0
                                                                   -4.00          -0.12
 -4.00              -0.25                                      -4.00          -0.25
                                                                   -4.00          -0.37
 -4.00              -0.5                                        -4.00          -0.5

So that means that tools differ at steps for cylindrical power (at 1.6 at 0.12D, at 1.5 at 0.25D), but steps in spherical power are the same -0.25.
We use calculation program for SATISLOH - rXpert. 

Could somebody explain it how it is possible that cylindrical step of tools differs between materials 1.5 and 1.6 if the same tooling index is used ?

2. If the tool index 1.498 is used for 1.67 material, the power off errors is about +/-0.84D. When i did any calculation in rX program, i was able to see not bigger deviance like +/-0.0625D. Because in the rXprogram i can see the "real" curve or tool and rounded curve or tool.
How should i understand the theoretical deviance +/-0.84D at 1.67 material with 1.498 tooling index ?

3. Tools compensation -  Does it work like this ? if i have tool of SPH:-9.00 ; CYL -9.75 i should be able to measure the -9.03 ; CYL -9.78.. Am i right ?
does it rule for all tools and is there any connection with lens thickness ?

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## essegn

> One other possibility to  mention and I saw it no where in the post, but would you be possibly  using an MR3 coater or mini? I went into a lab about a month ago and  they were having tons of issues..first told me power and than when they  sent me some samples I was locating tons of aberrations off center...  called and asked them to check powers coming right off the line BEFORE  coating.. and tada..it was the backside coater...had them dip the lens  in  heated distilled water in the tint unit and the "power problem" was  solved....


WE use the mr3 coater, but we have power off problems before we use  coating machine. Maybe the problems with power off causes the ultrasonic  cleaner that is ordered after production hall. I will check it.




> If it is a "lap"  issue you should be seeing a pattern to the lens powers vs.. index ...  if you did than you could always just run a compensation chart to set  you cross/base and tools or just let the compensated tool bring it  in...more chance of swirls/waves if you do not compensate both cut and  tool though.. sometimes spending a lot to solve a little can be  corrected with a "free" work around..
>     Poor guys answer to buying laps in 6ths..or even 10ths...
>   Just a thought of something I did not see mentioned.....
> 
> Jeff T.


I believe that problem lies in front curves with combination to lap  tools. Could you have a look at my previous message in this thread -  point 3 ?
Where can i find the pattern to lens powers vs index ?
how to work with compensation chart ? Like that - the used lap tool was  SPH -1.00, CYL -1.50, and result power was -0.02 out of tolerance, so i  set there for used lap tool compensation 0.02 ?

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## Jeff Trail

You most likely will have to go in and see how your surface program is picking compensated tool curve selection.. you maybe able to refine the round off point where it either goes up or down when selecting a tool that falls "inbetween" ...running 12ths on a 1.67 index will be a nightmare in both sphere or spher/cyl. combination .. just due to what the curve (base/cross) will do to how much effective power you end up with...
   Take for instance you if your program is rounding tools and you are running a cr39..the curve you need falls between and the program rounds it "up" a 12th...what you need is -7.41 and it gives you a tool of - 7.50 in CR39 you come out say a 12^ off.. no big deal... but say the program is not taking into consideration the effect of tool compensation and it rounds off the same way... it jumps to being a .25^ to a .37^ off ... your program possibly is not taking into account the curve vs. index and resultant power as it should... if you can not change the compensation does it give you a choice of tool curve? ie., 6ths 10ths ?? you could always run that "seldom run job" under the compensated and than you know which way to go, up or down on your actual 12th tools.. remembering curve vs. final power is multipled by the index of the material

      as far as a compensated chart... you could basically set of a statistical chart and show what tools were picked and the resultant power.. it would not take long to see a pattern of how much it was off based on power vs. tool ..if it is all the same material you'll be able to build you a working compensated chart... it is not going to be exact as running tools in 10th 1.67 or 6ths as you should with 1.74 but it would keep you in the ball park..

     I feel for you, it is a small percentage of your production but an expensive mistake and make it hard to dicide to "over invest" to correct the few or live with the frustration... or there is always the answer of routing it out to a secondary lab set up for this and you get the lens uncut and just do the edging.. no or little profit vs. inhouse but no breakage loss and frustration

Jeff "grind em till the scream" Trail

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## Fezz

Jeff,

I am so glad to see you posting!
Thank you for sharing your knowledge and experience with us!

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## readyslinks

Hi Guys!
I just got 2 used coburn 5000 cylinder machines.
Unfortunately one which i used for polishing developed fault,i switched over and started using the smoothing machine for polishing but the lenses come out with waves.
I need help to resolve this.
I will also like to know if their is any difference between a smoothing machine and a polishing machine.
Thirdly,what is the recommended speed,pressure, and time for polishing cr.39 lenses.
I look forward to your kind help.
Regards
Okafor

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## Jeff Trail

you can also set "stroke" as well, waves are going to be either pressure or heat, to much pressure causes friction (heat) ...make sure that the polish is hitting the lap and not just spraying over the top and off ... that layer of ploish between pad and lens is as important as just spraying polish everywhere ... I would get a gauge to actually check head pressure, depending on the dials is a no no... make sure you have even pins, make sure the polish is flowing where it needs to, check the clamp pressure or down pin pressure, ... do NOT run it on high, you are going to most likely increase the wave issue... also check the stroke length of the head to table... if it was going from a finer to polisher, the head pressure is probably to high ... I was always amazed how people turned up pin pressure and cut cycle times trying to compensate and save a little time.. I have seen them set so high it was shoving the axis pins back out :-)

  I would start with the basics and make sure the nozzle is set correctly spraying the polish, than move to testing the pin pressure... you may also want to make sure that the wobble assembly is right and you are getting the right motion, another thing that can generate unwanted heat.. check your polish temps as well..

   I can not remember the exact head pressure, it has been a very long time since I ran rockets.. keeping these Toro's running to speed would drive anyone to drink... I am sure someone can rattle off the #  for you .... 

Jeff " time to play Sherlock Holmes" Trail

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## essegn

I have questions about lap tools tolerance..

Which tolerance do you use for lap tools? For example lap tool of +2.00.. I measure +2.05 and i'm not sure how to set up the range of tolerance. I know that the smaller tolerance the better power results..
I would like to know the tolerance you use

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## MikeAurelius

use a sag guage instead of a diopter guage, much more accurate.

Sag tolerance: +/- 0.02 mm of sag results in +/- 0.031 diopters.

Also, when cutting (if you are using a mechanical lap cutter instead of a generator), after you've hogged the excess material off, use a last cut taking about 1/10th of a mm off, and slow the sweep speed down so you get a very smooth surface. Irregular surfaces will transfer to the pad and can result in uneven fining.

Your off tolerance could be from a variety of factors, but it is usually because your pad thickness hasn't been taken into account. How that is done depends on the type of lap cutter you are using.

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## Darryl Meister

> use a sag guage instead of a diopter guage, much more accurate


Just keep in mind that all of these instruments actually measure sagitta; any gauge or instrument that reads off in diopters is just converting a sag value into a dioptric reading by assuming a tooling index. And, to a "first order" approximation at least, sag values and diopters are directly proportional to each other.

Best regards,
Darryl

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## MikeAurelius

> Just keep in mind that all of these instruments actually measure sagitta; any gauge or instrument that reads off in diopters is just converting a sag value into a dioptric reading by assuming a tooling index. And, to a "first order" approximation at least, sag values and diopters are directly proportional to each other.
> 
> Best regards,
> Darryl


True, but most of the diopter guages I've seen don't have much in the way of resolution, which is why I prefer a direct reading sag guage. I've got three: two analog (dial type) that read to 0.01 mm with 50 mm round bars (no ball ends) (one for plus and one for minus), and one digital that reads to 0.001 mm. The digital is used to read base curve sags on all lenses, the analog for plus is to read tool curves and the analog minus is to read lens curves. We used to have another plus/minus set with 35 mm bars, but since plastics have taken over much of the high minus work, we converted them to other uses.

It's also important to check your sag guages from time to time with a master lens of a known curve or saggita depth. Guages out of calibration will mess not only with your head but also your end results.

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## Darryl Meister

If you have access to a Younger Gauge Master, it has some calibration curves that you can use for calibrating many bar gauges, but not bell gauges. RH Burton (*RH Burton*), now National Ophthalmics, was distributing these for a while, although I'm not certain whether they still offer them. I imagine that some of the lab machinery or lab consumable companies out there will offer some different tools for checking the calibration of sag gauges as well.

As for establishing tolerances, this ultimately boils down to controlling the propagation of errors. Power errors are incurred by errors in curvature of the front surface, errors in lens thickness, and errors in curvature of the back surface. The front surface can be off by up to 0.09 D according to ISO manufacturing tolerances. And the lens thickness can be off by up to 0.3 mm according to the ANSI Z80.1 standard.

For the back surface curvature, your lap tools introduce randomly distributed rounding errors equal to one-half of the lap tooling increments or less. And any error due to the curvature of the lap tool will either increase or decrease the final error. Consequently, the increments of your lap tools should be a factor in this decision. For instance, compared to eighth-diopter tooling, a tenth-diopter tool can be off by an additional +/-0.0125 D without exceeding the same potential rounding error of an eighth-diopter tool.

Best regards,
Darryl

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## Rafael

Esseng, contact Chris Bowers a member on optiboard. He has a great excel sheet for simulating rounding errors on different tooling index and tooling steps and shows you also how many tools you will need, maybe he can help you.

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## Darryl Meister

Yes, the refractive index of the actual material is also an important factor. For eighth-diopter tooling, the rounding error ranges from +/-0.059 D for hard resin to +/-0.087 D for 1.74 high-index. For tenth-diopter tooling, on the other hand, the rounding error ranges from only +/-0.047 D to +/-0.070 D.

Best regards,
Darryl

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## Rafael

The Tool is on optiboard, you can find it in this threed:

http://www.optiboard.com/forums/show...906#post297906

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## MikeAurelius

I can make glass curve masters if anyone needs them, we have master curve plates that are tracable back to nat'l standards. Let me know if you are interested.

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