Cooke Series VI Portrait Lens Disassembly and Cleaning.

[Colin D]

I'm not familiar with those.
I would not recommend disassembling the aperture unless nothing else works. I've had some shutter apertures apart and they're a PITA to reassemble especially if they have 11 or more blades.
Apertures have two plates, a fixed one usually permanently attached or a machined part of the barrel, and a moveable plate that is operated by the aperture ring via a pin or special screw. The blades are arc shaped, have a pin in each end, and the ends are usually different but look similar. The movable ring has a lubricant between it and the barrel from the factory that dries out and micro fine particles of brass or bronze from the pins wearing and dust collects in the lubricant aiding the sluggishness. A stuck aperture has dried lubricant or corrosion causing it to stick. Flush or soak it in solvent until it moves. Never force an aperture, blades can buckle and break.
90% Isopropyl Alcohol is a good solvent to soak in. The contact cleaner recommended in post 5 uses a combination of Alcohol and Naphtha.

Many thanks for your response, one of the screws I mentioned appears to move the iris blades when the aperture ring is turned. I can see via a hole on the inside of the barrel where the screw goes through the external tube into the internal tube. I've been reluctant to remove it without knowing what would happen and will leave it like that unless the solvent fails.

The other screw which lies close to the first one sits higher but I can't see what its purpose is.

I'll give the CRC solvent mentioned in the thread a try over a week.

Colin d

 

[shutterfinger]

There is a slot in the barrel that the operating screw slides in. If the aperture gets turned beyond the slot to where the screw hole is no longer visible in the slot its easy to turn the movable plate to where its accessible. The second screw might be a tension adjustment on the aperture ring ( all I can think of at the moment).
Once the aperture moves when dry apply the dry lubricant to the blade pivots and movable plate.

 

[Europan]

You have a triplet there. The Cooke portrait triplet has a strong positive power element at the rear and that is the one whose distance setting is most critical. The middle element is a biconcave lens and I should remove it as well, if I wanted to use the instrument. Don’t worry about its position, it has its own seating and will come back right in place for you. You will have to cement it back in. The iris should work properly, otherwise the lens is of limited use.

Prices have gone wild. Although of a certain age, it’s only a triplet and I shouldn’t pay more than $200-300 for such a lens. It is not bloomed.

 

[Colin D]

90% Isopropyl Alcohol is a good solvent to soak in. The contact cleaner recommended in post 5 uses a combination of Alcohol and Naphtha.

When you say soak do you mean putting it in a bath of solvent, covering the whole aperture system (no cells) or just giving it a good spray?

 

[Old-N-Feeble]

You have a triplet there. The Cooke portrait triplet has a strong positive power element at the rear and that is the one whose distance setting is most critical. The middle element is a biconcave lens and I should remove it as well, if I wanted to use the instrument. Don’t worry about its position, it has its own seating and will come back right in place for you. You will have to cement it back in. The iris should work properly, otherwise the lens is of limited use.

Prices have gone wild. Although of a certain age, it’s only a triplet and I shouldn’t pay more than $200-300 for such a lens. It is not bloomed.

I got approximately $550 for a Cooke 13" triplet nearly three years ago, and that one had a missing lever. Otherwise it was fully functional with flawless glass.

 

[shutterfinger]

Soak as in sumurge if a spray out doesn't do it. Put it in a small jar, pour or spray in enough solvent to cover the aperture, cover with the lid to slow/eliminate evaporation and let sit for a half hour or more.

 

[Colin D]

Soak as in sumurge if a spray out doesn't do it. Put it in a small jar, pour or spray in enough solvent to cover the aperture, cover with the lid to slow/eliminate evaporation and let sit for a half hour or more.

Solvent didn't make an impression so I took out the screws and removed the front barrel and f stop ring. Now I've got to separate the two cylinders that hold the iris diaphragm which is still stuck. Once I separate them I should get access to the gunk stopping the aperture from working, and to the blades which are not properly seated now and bulging in places. Both cylinders are firmly joined by a screw thread. I've been told by an experienced LF user to put rubber on both ends of the cylinders and use strong pressure while turning. I'll try that and hope it works.

 

[shutterfinger]

Once I separate them I should get access to the gunk stopping the aperture from working, and to the blades which are not properly seated now and bulging in places.

Be very careful here, bulging blades not seated are ready to bend or break.

I speculate its corrosion that has it stuck. I would apply penetrating oil to the barrel halves seam and let it work for a few hours. You can flush the oil out once they're separated.
https://www.amazon.com/LIQUID-WRENC...d=1492658225&sr=8-19&keywords=penetrating+oil

 

[Colin D]

Be very careful here, bulging blades not seated are ready to bend or break.

I speculate its corrosion that has it stuck. I would apply penetrating oil to the barrel halves seam and let it work for a few hours. You can flush the oil out once they're separated.
https://www.amazon.com/LIQUID-WRENC...d=1492658225&sr=8-19&keywords=penetrating+oil

Ok I'll give that a go. I've tried everything else so this is my last resort before using force.

 

[shutterfinger]

Make sure you have not missed a pin or screw.

 

[Colin D]

Make sure you have not missed a pin or screw.

After giving it a good does of Loctite Freeze & Release I was able to get all the blades out. There were two rings holding them in I was finally able to move.

Next problem, some of the blades are damaged, not broken but warped, is it possible to repair them or is it easier to replace them? I'm thinking replace, maybe, as they are delicate and getting them back to original state could be near on impossible. The only way I thought it might be possible is to heat them until they become soft, flatten them again and dip in warm water to cool them down, like a blacksmith would do. Or is it as simple as getting another old lens and replacing them, sounds too easy to be true. I imagine the f stop will have something to do with getting blades to match.

Thanks again for pointing me in the right direction.

Colin

 

[Colin D]

This has become an obsession and case study in perseverance. I've completely dismantled the lens. Some of the blades are warped, bent in places, mighty ugly, my heart sunk to my feet. My first thought was I had ruined this lens as a fully working one. I took a step back and began thinking through the likely ways to fix this, even though I had read this was practically a lost cause.

Without great expectations I began the process of trying to repair the damaged blades which I thought might be impossible given they are so fragile and pliable. With a bit of research on metal work forums I came up with a method of working to straighten then flatten them out. Straightening was simply done by hand to get them as good as I could manually, but still with noticeable kinks in the metal that would make them unusable. Next step was a matter of using a round metal handle of an old salad server to roll over the blade gently, the blade was on a block of hard sponge like material I found on the road so that there was some give when I put light pressure on the blade. That gave me an improved smoothness of the blade but it was now semi curled from the process and still with kinks that were barely noticeable but a problem. Next step was to place the blade on a smooth flat metal surface and run the cylindrical handle over it with minimal but increasing pressure, this was done a number of times, occasionally turning it over. Eventually I had a flat blade again. On the test blade there was a small bur in the inside curve where it had been bent. This I removed using a very very fine small well smoothed Arkansas oil stone I've had since a kid in my fishing tackle box.

The test blade appears acceptable, to me at least, using this process, I'll now do the others and re-assemble the aperture and see if I have succeeded in achieving what I thought would be impossible to get it back to working condition. From what I've read it is a challenge to get the blades back into the aperture mechanism, and there is a precise method to lining up the mechanism so it opens and shuts to the f stop it is meant to be at. With this lens I think it relates to lining up the screw hole that holds the inner and outer barrels in alignment. If I get that far then that is the least of my problems.

 

[shutterfinger]

I use smooth jaw needle nose pliers to flatten burs on blades. Smooth jaw duck bill pliers should work also. I prefer a block of hardwood sanded glass smooth and a plastic mini screwdriver handle for the stubborn ones when pressing is necessary. Metal forming 101.
Aperture assembly is on the fixed side pick a starting point (does not matter) and insert the blade pin in the hole and position the blade at the wide open position. Proceed in a counterclockwise (anti clockwise) direction laying the next blade on top of the previous. You will come to a point where the next blade will need to slide under the 1st blade to reach its fixed hole. This is where it gets tricky and there is no rule other than to be gentle.
If the back side of the fixed ring can be accessed then put painters tape over the holes and press the pin into the tape to help hold it in place while sliding a blade under the first few blades.

My best was the third try on an 11 blade Compur, the worst 10th try on a similar shutter.

 

[Colin D]

I use smooth jaw needle nose pliers to flatten burs on blades. Smooth jaw duck bill pliers should work also. I prefer a block of hardwood sanded glass smooth and a plastic mini screwdriver handle for the stubborn ones when pressing is necessary. Metal forming 101.
Aperture assembly is on the fixed side pick a starting point (does not matter) and insert the blade pin in the hole and position the blade at the wide open position. Proceed in a counterclockwise (anti clockwise) direction laying the next blade on top of the previous. You will come to a point where the next blade will need to slide under the 1st blade to reach its fixed hole. This is where it gets tricky and there is no rule other than to be gentle.
If the back side of the fixed ring can be accessed then put painters tape over the holes and press the pin into the tape to help hold it in place while sliding a blade under the first few blades.

My best was the third try on an 11 blade Compur, the worst 10th try on a similar shutter.

Thanks, I'm only up to my fourth blade of 12. One shows faint signs of where it kinked in the form of two shiny lines, running the finger over they are barely noticeable, I'm unsure of the tolerance to a not quite perfectly flat surface will be. To the eye it appears straight enough to mount, I'm hoping once they are all in place and using some graphite powder and working them back and forth it will wear enough to provide a smooth enough contact surface with rub spots but workable.

Good tip using the painters tape, I'll keep that in mind.

 

[Colin D]

I use smooth jaw needle nose pliers to flatten burs on blades. Smooth jaw duck bill pliers should work also. I prefer a block of hardwood sanded glass smooth and a plastic mini screwdriver handle for the stubborn ones when pressing is necessary. Metal forming 101.
Aperture assembly is on the fixed side pick a starting point (does not matter) and insert the blade pin in the hole and position the blade at the wide open position. Proceed in a counterclockwise (anti clockwise) direction laying the next blade on top of the previous. You will come to a point where the next blade will need to slide under the 1st blade to reach its fixed hole. This is where it gets tricky and there is no rule other than to be gentle.
If the back side of the fixed ring can be accessed then put painters tape over the holes and press the pin into the tape to help hold it in place while sliding a blade under the first few blades.

My best was the third try on an 11 blade Compur, the worst 10th try on a similar shutter.

Well I finally finished putting the blades back in after getting them as smooth and flat as I could. Here it is nearly to the finished stage, the blades work fine but the opening and shutting of the blades is still stiff, the only thing I can think of to try now is lubricant.

Flattening each blade took extreme care, I rolled a stainless steel round spoon handle over them, firstly on a sponge to flex out the kinks then on a porcelain tile to flatten out the curling each end that occurs in the first step. It took me over a week to complete this alone.

The process was long and laborious and seating each blade individually was a test of patience, particularly with the last four when I couldn't see their holes to set them into because of the other blades covering everything. With careful sliding, lifting, placement and re-arranging along the way I got them in. Your advice to do them at fully open position was invaluable in the end. Thanks for your help.

 

[shutterfinger]

Here it is nearly to the finished stage, the blades work fine but the opening and shutting of the blades is still stiff, the only thing I can think of to try now is lubricant.

Extra fine powdered graphite. Close down to its smallest opening, sprinkle liberally, wipe onto the blades and pivot pins with a cotton swab until evenly coated, shake out the excess, repeat for the other side. With with the blades, not against their arc. Apply graphite or trace of light weight grease in the base of the slot where the operating ring screw(s) go also.

Nice job so far.