I Hate Slab-offs

**Mike Fretto** · 11-07-2001, 09:51 AM

I must be a glutton for punishment, in an effort to save my employer some money in these hard times, I have been grinding slab-offs in our office for about 6 months now with pretty good success. There are a couple things I've noticed I would like to get some input on. First I feel it necessary to provide the following info, we use DAC's slab kit to make the dummy lense, we also have Gerber/Coburns premier lab setup, Step-one blocking, SGX generator, and Acuity finer and polisher. One of the problems we've had is certain materials dont seem to be slab friendly so to speak, Spect. Trans for one we've ruined a couple trying to remove the dummy lense, it almost seems to tear the material of the lense???? I've tried other epoxies but with no more luck than with DAC's. One suggestion I recieved here on Optiboard was to try Devcon 2- ton Epoxy, this stuff got so hot it melted the wax holding the lense to the block we mixed up another tube and checked the temp. with a digital thermometer would you believe 170F. Another problem we've had is the dummy lense comes apart in the center of the lense, we mix according to Dacs recommendations and cure a full 24 hours before grinding, Ive also backed off on stock removal in the generator. We try to tell the dispensers to hold off on the special materials so we can use reverse slab's, one reason being the patient in most cases will be having surgery on the other eye in the near future then the need for slab offs is no longer there. BUT NOOOOO they insist on selling the special stuff that cant be provided in reverse form. So I guess what I'm asking for is some suggestions that work on what epoxies to try. Thanks in advance

**Darryl Meister** · 11-10-2001, 01:18 PM

Hi Mike,

I'll preface this by saying that I certainly don't do many slab-offs in technical marketing ;)... However, I have done a couple of slab-offs successfully on Spectralite before, using a 5-minute quick-cure, two-part epoxy from a local hardware/hobby store (I've forgotten the brand). I taped the periphery of the lens, mixed the epoxy in the plastic cup that the lens was packaged in, and then poured the mixture onto the surface. I ran the job about 10 or 15 minutes later, and removed the dummy epoxy by soaking the lens in the reclaim tank for a few seconds. Seemed to work quite well. I haven't tried on any on Spectralite Transitions though.

Best regards,
Darryl

**Jeff Trail** · 11-21-2001, 10:04 PM

Missed this one, glad it's a holiday weekend and I can see all the things I missed

Mike, one of the better ones I found is using just plain ole table resin and hardner.. it's cheap and easy to remove.. same way Darryl went about it.. take some scotch tape place it around the lens like a bowl and pour in the resin (with hardner mixed in) .. one thing though as this sets it has a chemical reaction and generates heat and the lens always deblocks.. so one of the tricks I learned is to take a fine marker and make all my marks so they are easy to see after taping and blocking.. I also like to take that marker and place a str8t line along the seg line (across the whole lens) on the front surface, makes it very easy to keep the slab line str8t and you don't have to hold t up and look for that hard to find seg at times, especially if it's a low powered add.
Plus you don't have to use the reclaim tank that resin just pops off and when surfacing it really makes it easy to cut the lens since it acts almost like cr39 when surfacing.
For as cheap as it is, I have two small cans and they have been around for a couple of years it might be worth trying both ways to see which works better for you.. I think I might give Darryl's a try to see if I like it better than the resin...

Jeff "always looking for the easier way" Trail

**MervR** · 12-03-2001, 07:56 PM

I've done a ton of slabs and loved everyone of them

First off put the line across the lens so you have a reference line.

Second the 5 min epoxy I like the best is from lepages it is a 2 part.

Works great just straight on the lens for cr39, glass and poly but for 1.6 and such I would put a piece of surface tape on the upper part of the lens.

the tape will fine off if you come down a little far.

The BIGGEST thing to do is put the lens in water, right up to the edge of the lens. the colder the better.

The Idea I liked from one of the other posts was the tape around the lens so you can make the epoxy deeper.

With the good ol 507 coburn cyl machine and a loh blocking and generating system these are a breeze, but if we tried these on are loh cyl's it would lose some of the prism because it uses a air filled chuck, so just cut extra if you find you are losing some prism. (not familiar with your equipment.)

MervR

Good luck

**rob in uk** · 06-10-2009, 04:36 AM

Originally Posted by Jeff Trail

Missed this one, glad it's a holiday weekend and I can see all the things I missed

Mike, one of the better ones I found is using just plain ole table resin and hardner.. it's cheap and easy to remove.. same way Darryl went about it.. take some scotch tape place it around the lens like a bowl and pour in the resin (with hardner mixed in) .. one thing though as this sets it has a chemical reaction and generates heat and the lens always deblocks.. so one of the tricks I learned is to take a fine marker and make all my marks so they are easy to see after taping and blocking.. I also like to take that marker and place a str8t line along the seg line (across the whole lens) on the front surface, makes it very easy to keep the slab line str8t and you don't have to hold t up and look for that hard to find seg at times, especially if it's a low powered add.
Plus you don't have to use the reclaim tank that resin just pops off and when surfacing it really makes it easy to cut the lens since it acts almost like cr39 when surfacing.
For as cheap as it is, I have two small cans and they have been around for a couple of years it might be worth trying both ways to see which works better for you.. I think I might give Darryl's a try to see if I like it better than the resin...

Jeff "always looking for the easier way" Trail

Hi Jeff,
I know it was a long time since you sent this article about slab offs but how do you keep the line straight when sufacing an oblique axis?
We always have to use the Youngers lens which can be expensive and special order

Rob England

**humbleABOCtx** · 06-25-2009, 12:41 AM

I cannot answer the techi questions but I did find out rather quickly (yrs ago)....IF YOU DONT want a lab tech to throw a sent of lenses atyou...DONOT SELL POLY-SLAb!!!! I was told slips too easy..+ they have to reprocess alot more often compared to CR-39 or HIP.

For P-sat/Communication issues, tell pt's 2 OR MORE weeks/// "2-3 weeks" if youre adding AR etc!!!!!
(for standard lab ordering-this doesnt include you lab god's out there...+ I know you're out there).

SUGG. if Rx expected to change/fluxuate over a few months DON't upsell until the final order is placed. These pt's tend to need their glasses rather quickly in my experience.

**hipoptical** · 06-25-2009, 10:43 AM

Digital slabs... only way to go. Any material, any treatment, any add-on- without any problems.

**rob in uk** · 06-26-2009, 03:04 AM

Hi thanks for the reply but: "Digital slabs"?

Do you mean freeform? over here never heard of digital slabs only the conventional or Youngers slab on.

Any info greatly appreciated
Thanks

Rob
England

**Jacqui** · 06-26-2009, 06:49 AM

Digital slabs are the same as Younger and a few others, they are freeform.

**hipoptical** · 06-26-2009, 07:53 AM

Digital slabs are made on certain "freeform" generators only. You have a lab over there that has the capability. The process is simple for them, and the possibilities are endless: slab, reverse slab, split- pretty much whatever you want, including materials, transitions, and polarised lenses. The line can be virtually invisible or prominent, whatever you prefer.
Sooner or later digital lenses will take over. Resistance is futile...

**Jacqui** · 06-26-2009, 08:35 AM

check this out from DAC International http://www.dac-intl.com/equipment-sp...-lens-menu.htm click on the blended bi-centric tab.

I wish we still made them out of glass with a hand polising bowl.

**gemstone** · 06-27-2009, 05:24 AM

Originally Posted by Jacqui

check this out from DAC International http://www.dac-intl.com/equipment-sp...-lens-menu.htm click on the blended bi-centric tab.

I wish we still made them out of glass with a hand polising bowl.

They were sure prettier then. There are some tricks a good surfacing man can do to make them nicer.

**hipoptical** · 06-29-2009, 02:34 PM

1. Tricks not required when processed digitally.
2. It doesn't get much "prettier" than a slab-off with no visible line AT ALL.

**gemstone** · 06-29-2009, 05:01 PM

Originally Posted by hipoptical

1. Tricks not required when processed digitally.
2. It doesn't get much "prettier" than a slab-off with no visible line AT ALL.

Nor more expensive. But admittedly requiring no skill.

**hipoptical** · 06-30-2009, 08:19 AM

Originally Posted by gemstone

Nor more expensive. But admittedly requiring no skill.

I agree and disagree. The one problem I have with the digital age... it is easy to make near-perfect lenses, but there is little-to-no knowledge of optics required. There is "skill" involved, but it more a working knowledge of computers and the ability to envision a lens as a work of computer-generated art. Optics and manual dexterity are optional skills that will be rarely used.
I think we will soon see that with edgers like Santinelli is making coupled with digital lens generating systems, a new hire will be producing high-end, complex eyewear within a couple of days. I am not saying this is a good thing- but it is the direction we are heading. I think it is more important now than ever that those with knowledge and skill adopt the new technology, before it is taken over by idiots.

**gmanlook** · 07-13-2009, 06:01 PM

Just wanted to say that I managed a specialty lab for many years and this is what I know...we used "table top resin" of course we bought it in 5 gal. buckets...made sure that the lens to be slabbed was clean...we then used regular scotch tape and wound it around the lens...the epoxy we added a small amount of dye to get some contrast to be able to see the line.....But on the 1.67 and spectralite what we did was we saved the slab material that was removed from previous jobs and used a spray adhesive (from 3M used for mounting pictures ) spray the lens with the adhesive and heat up the slab material on a hot plate...when it gets pliable spray the adhesive on the slab material and stick it on the lens...within 10 min you can generate it (I had the Optek SL) afterwards the slab comes right off with a little heat......I know too well the woes of the stuck epoxy on a hot job and an expensive lens...hope this helps...Gary :idea: