# Optical Forums > Ophthalmic Optics >  How to Edge Bifocals and Progressives.

## Kerbear888

I need serious help. I am a licensed optician, who hasnt done any edging since school. I am managing a new office and our lab guy just quit. I need help on figuring out the measurments for blocking bifocals and progressives. I am fine doing SV. I know it has something to do with the B measurment. 

Someone please help me.

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## Joann Raytar

Kerbear888,

Welcome to OptiBoard!

What type of equipment are you using?

If you are using a blocker like the CS-7, you need to take half the B measurement and algebraically subtract the fitting/seg height from it to get your decentration.  A positive result means move the lens down; a negative result means decenter up.

*Example 1:*
B = 40
seg height = 15

40/2=20
20-15=5
Move lens 5mm down

*Example 2:*
B=40
seg height = 25

40/2 = 20
20-25= -5
Move lens 5mm up

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## hcjilson

Call your lab and see if they have some old blanks from jobs that have been returned that they could send you to practice on a couple, just to make sure. If they don't have any, just ask for  10 pair coquile lenses...practice is less expensive than imperfect.

If you find that you find yourself backed up by trying to do front and back too, have your lab do the work complete, it will usually be cheaper than the warm body that just quit!

Good luck I do not envy you!:D 

hj

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## Dannyboy

try the program from steve optical calculation in the downloads 
(at the top of the screen)

Dannyboy

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## edKENdance

It would be great if there were a common-sense book out there.  Perhaps there is and I don't know about it.  I just learned today how to lay-out a circular seg for a spherical correction.  It's very simple to do but since I might see only one every couple of months it is going to be nearly impossible to remember.  I took the smart path and wrote it down so I have it on me.

Hopefully you didn't have specific heights on your sv's because it uses the same principle.

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## Jubilee

Equipment setup is important here..

Some edgers require offsetting at layout for seg heights and pd. So any movement of the OC and seg to match the fitting requirements must be done at the blocker.  

On the old manual blockers it is a matter of finding what offset is required. So if you have a 40mm B and a seg of 15... you need to go down 5.  If the Frame PD is 70 and the patients pd is 60.. The required adjustment is to set the seg at 5in and 5 down. Please note that if you are using lined bifocals, the near pd is used for the inset calculations. 

Some newer blockers have a digital controls. You view the placement of the lens on screen and get the seg, or the OC in the middle, axis lined up on the 180, and program in the mono PD and fitting height, and the blocker will make the appropriate calculation and automatically blocks it for you.  

Some edgers can offset on their own. For instance, Santenellis. You always put SV on center, and progressives seg on center, and the lined bifocal is 0in 5down.  It has controls on the machine itself to set pd and fitting heights. 

If you want to list what equipment you have, we might be of better assistance and can give you a step by step approach.

Cassandra

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## Darryl Meister

_Essentials for Ophthalmic Lens Work_, by Clifford Brooks, is a pretty straightforward book on lens finishing.

Best regards,
Darryl

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## harry a saake

Ed and the rest, on page 7 of my TIPS ON DISPENSING THREAD, i wrote a post on how to correctly layout round seg lenses.

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## edKENdance

I should have written that down when I read it the first time and I might have remembered it. :hammer:

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## lestronomus

On the PAL's, shouldn't you be using the mono PD in case PD is R29 & L31? 


Some edgers require offsetting at layout for seg heights and pd. So any movement of the OC and seg to match the fitting requirements must be done at the blocker. 

On the old manual blockers it is a matter of finding what offset is required. So if you have a 40mm B and a seg of 15... you need to go down 5. If the Frame PD is 70 and the patients pd is 60.. The required adjustment is to set the seg at 5in and 5 down. Please note that if you are using lined bifocals, the near pd is used for the inset calculations. 

Some newer blockers have a digital controls. You view the placement of the lens on screen and get the seg, or the OC in the middle, axis lined up on the 180, and program in the mono PD and fitting height, and the blocker will make the appropriate calculation and automatically blocks it for you. 

Some edgers can offset on their own. For instance, Santenellis. You always put SV on center, and progressives seg on center, and the lined bifocal is 0in 5down. It has controls on the machine itself to set pd and fitting heights. 

If you want to list what equipment you have, we might be of better assistance and can give you a step by step approach.

Cassandra[/QUOTE]

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