Unwanted Prism on bifocals

**Yomandinga** · 10-16-2008, 02:21 PM

First off I just want to say a big hello to everyone on my 1st post so hello. =D

Ok on to business, I recently got promoted to Lab Manager and the new lab I am running has a Coburn 1008 generator which is causing me no end of grief with bifocal lenses. For some reason i am getting unwanted out and down prism in the lenses and with little knowledge on the machine I have no clue how to rectify this. At 1st I thought maybe I was putting the prism ring on the wrong side of the prism axis line but after trying it both ways around I realised I was doing it correctly to begin with, next I thought hmm maybe I'm not lining it up with the thinest point on the ring again I found I was doing it properly so that was out the window. I adjusted the nozel on the alloy blocker since the genius in the lab before me decided it was a good idea that the blocks shall not sit properly on the ring.

I have had one succesful solution which involved doing the lenses at 2 in 5 down instead of 5 in 5 down and then using the 0.00 prism ring which has given me lenses with no prism and the correct powers but I would like to do things properly so I need a real solution to my problems (one that doesn't involve taking an axe to the poor old rocket) I think if the problem was occuring on all lenses I would be able to come up with the answer myself but for it to only happen on D28s I'm just well I guess confused would be the best word to describe it.

Sorry to have gone on for so long but if anyone has any helpful advice I would be extremly grateful.

**Fezz** · 10-16-2008, 03:22 PM

Welcome to Optiboard!

:cheers::cheers::cheers::cheers:

**Jubilee** · 10-16-2008, 03:35 PM

I take it this is the 108CT?

Nice thing about this machine is that it is almost pure mechanical beast. So no need to worry about encoders and all that crud.

So the prism is ALWAYS down and out?

Do you notice if OC's are out of the geometric centers on SV, and how is your PAL's doing? Any discrepancies there?

You use alloy. How long do lenses sit before generating?

Have you checked the quill, chuck, and wheel position?

And is it all Bifocal lenses or a particular brand? (sounds crazy about brands, but I have seen where Calc programs have wrong info keyed in..)

Congrats on the promotion and welcome to Optiboard!

**optical24/7** · 10-16-2008, 03:46 PM

Are your blocks being raised/interfered with the seg itself?

**Yomandinga** · 10-16-2008, 03:55 PM

Thanks Fezz

Originally Posted by Jubilee

I take it this is the 108CT?

Nice thing about this machine is that it is almost pure mechanical beast. So no need to worry about encoders and all that crud.

So the prism is ALWAYS down and out?

Do you notice if OC's are out of the geometric centers on SV, and how is your PAL's doing? Any discrepancies there?

You use alloy. How long do lenses sit before generating?

Have you checked the quill, chuck, and wheel position?

And is it all Bifocal lenses or a particular brand? (sounds crazy about brands, but I have seen where Calc programs have wrong info keyed in..)

Congrats on the promotion and welcome to Optiboard!

Its a Coburn 1008 Rocket

The OCs on s/v are fine and I've had no problem with PAL's

The Alloy is usually left to cool down about 10 minutes but the lab runs an hour service so sometimes it is about 5 minutes.

I haven't unfortunatly I don't have much knowledge on this machine and all of the calibration tools have gone missing over the years >_<

Now that I think about it the transition bifocals i use seem to come out ok so I guess it could be a program fault. Unfortunatly I can't alter any of it because Innovations has an admin password that only people at head office know.

Thanks for taking the time to answer =D

Originally Posted by optical24/7

Are your blocks being raised/interfered with the seg itself?

we have some of the Big 68mm blocks for doing bifs so the seg doesn't get raised up and the blocks sit flush on the ring since i altered the nozel.

Thank you for your reply too =D

**Andrew Weiss** · 10-16-2008, 04:06 PM

Ican't offer any techincal advice on this as I don't know the machine (my last exposure to surfacing was longer ago than you'd want to imagine), but I can say

Welcome to OptiBoard! :cheers::cheers:

**HarryChiling** · 10-16-2008, 04:17 PM

Your problem may be that you are blocking on GC rather than on OC, does your lab software give you a prism ring to use as well as a direction? If so then you need to use that ring at the specified direction, if not then you might need to block your FT's on OC and see what come of it.

**shanbaum** · 10-16-2008, 05:02 PM

Have you contacted your support desk with this issue?

**Yomandinga** · 10-16-2008, 05:58 PM

Originally Posted by HarryChiling

Your problem may be that you are blocking on GC rather than on OC, does your lab software give you a prism ring to use as well as a direction? If so then you need to use that ring at the specified direction, if not then you might need to block your FT's on OC and see what come of it.

It gives the ring to use and a prism axis and i've been matching them up right and still getting the problem. I tried blocking where the OC should be and used the 0.00 prism ring instead of the 0.20 prism ring the program was telling me to use and the lens came off nice but I wanna try and get it running properly if I can.

Originally Posted by shanbaum

Have you contacted your support desk with this issue?

I spoke to the companies training manager about the problem as he is also the most expieranced Coburn operator we have and all he did was go through the blocking procedure with me again. I guess its company policy not to admit we have a dodgey machine or program lol.

If I can't get it sorted soon i'm gonna start using my method on full production just be another bodge to add to my repotoir.

**Fezz** · 10-16-2008, 06:03 PM

Did the lab have these issues previously?

What has changed, what has stayed the same, what are the other variables?

**HarryChiling** · 10-16-2008, 06:18 PM

Originally Posted by Yomandinga

It gives the ring to use and a prism axis and i've been matching them up right and still getting the problem. I tried blocking where the OC should be and used the 0.00 prism ring instead of the 0.20 prism ring the program was telling me to use and the lens came off nice but I wanna try and get it running properly if I can.

I spoke to the companies training manager about the problem as he is also the most expieranced Coburn operator we have and all he did was go through the blocking procedure with me again. I guess its company policy not to admit we have a dodgey machine or program lol.

If I can't get it sorted soon i'm gonna start using my method on full production just be another bodge to add to my repotoir.

You think maybe it's printing the prism info on there but set to block on OC rather than GC? That's kinda what it sounds like, but who knows it coudl be the generator knomes that have been known to mess with things.

**MELVIN** · 10-16-2008, 08:05 PM

What type blocker do you have.

**shanbaum** · 10-17-2008, 08:42 AM

Originally Posted by HarryChiling

You think maybe it's printing the prism info on there but set to block on OC rather than GC? That's kinda what it sounds like, but who knows it coudl be the generator knomes that have been known to mess with things.

Not likely - if it were set to block on PRP, there wouldn't be any prism for decentration.

Yomandinga, send me a pm and tell me where you are. Also tell me what blocking system you're using.

**jherman** · 10-17-2008, 09:22 AM

pm me if you need one.

**HarryChiling** · 10-17-2008, 10:53 AM

Originally Posted by shanbaum

Not likely - if it were set to block on PRP, there wouldn't be any prism for decentration.

Yomandinga, send me a pm and tell me where you are. Also tell me what blocking system you're using.

Thanks Shanbaum I meant the other way around GC rather than OC. I didn't even notice that, the first post I think I had it right. I know in the older version of Visual Lab Pro the work ticket printed the prism and direction on it, I think even if you had it set to block on OC so that could be where the confusion coems from. I don't really worry too much about it 'cause I use Innovations, I like the feature that lets you modify shape by adding to the B size or scaling the lens up. I have really begun to rely on that feature a lot lately.

**Yomandinga** · 10-17-2008, 02:01 PM

Originally Posted by Fezz

Did the lab have these issues previously?

What has changed, what has stayed the same, what are the other variables?

Well the Lab Manager before me trashed the place pretty badly and the generator was left unused for months so I'm not sure. The guy had a reputation for breaking machines to get out of doing work so now I'm left picking up the pieces.

What type blocker do you have.

Can't remember off the top of my head i'll double check tomorow.

I found some old manuals today so I had a tinker with the machine and I have a couple more bifocal jobs to surface tomorow so I will let you know my results on them. Hopefully something was just out of line and it will be fixed XD ah if only it was an ideal world lol.

**shanbaum** · 10-17-2008, 02:06 PM

It would also be helpful if you would post the problem in more detail. How much unwanted prism are you getting? Down and out in both eyes?

Again, knowing the type of blocker, and layout marker (if there is one) is important. Having all the layout details would help too (not just LRP placement, but prism amount and direction as well); rx details, etc. It's very hard to diagnose a problem with scant information.

**Yomandinga** · 10-17-2008, 02:22 PM

Originally Posted by shanbaum

It would also be helpful if you would post the problem in more detail. How much unwanted prism are you getting? Down and out in both eyes?

Again, knowing the type of blocker, and layout marker (if there is one) is important. Having all the layout details would help too (not just LRP placement, but prism amount and direction as well); rx details, etc. It's very hard to diagnose a problem with scant information.

Yep will get that sorted for you tomorow got a few jobs in and will see if the retails staff can throw a few more bifs my way to give us a better picture I just hope my calibrating hasn't made it worse XD

**bob_f_aboc** · 10-19-2008, 08:11 AM

One thing to try is to flip the lens when blocking. I always had better luck with FT's by blocking with the seg on top half of the block. If you block with the seg on top, try it with the seg on the bottom. Also, be aware of the pressure you are putting on the lens when blocking. I have seen a lot of prism from techs in a hurry with an off center thumb.

I have used the 1008 and love the machine. It is a work horse and is usually very consistant. I think the prism issue is happening before you get to the generator.

Another thing to rule out generator error is to block the lens 90 off axis on a spherical job.

These are things I have come up with while running the beast.

Hope they help.

Bob

**James Peterson** · 10-20-2008, 04:57 PM

Yomandinga,
Welcome to Opti Board, sorry I cannot help you with this problem,
James Peterson:cheers::cheers:

**Yomandinga** · 10-22-2008, 03:45 PM

Hi sorry I haven't replied been ill so haven't been in work unfortunatly the jobs I was gonna make note of got done by someone else while I was away and I haven't had any bifs in the last few days but I have got a list of the machines for you to ponder over.

Marker = CS-7
Surface Tape= 3M Surface Saver System
Alloy Blocker = Coburn Optical 990
Cyl Machines = Coburn Toric Surfacer (with 1 side broken because they didn't lube the damn thing and the pin got stuck inside and I can't get it back out grrrr)
Generator = The ever loveable Coburn 1080

I'll get some prescriptions ASAP for you gotta get those Bifs selling unfortunatly we have hit a dip in Bif sales lately on a plus side varifocals are up up up lol.

I block with the add at the top its part of the companies best practice policy.

On a positive note I succesfully altered the thickness settings so now my lenses are coming out at a nice thickness ^_^

The truly annoying thing is I don't have a single calibrating tool for any of these machines which I bet isn't helping my situation.