Stiff/stuck aperture

[shutterfinger]

I'm open to tips on how to free up the aperture in a late teens to early 1920's Taylor-Hobson Cooke Series IIa barrel lens.

 

[Tom1956]

Inspect the blades as you try to move them to be sure they are not getting tangled up with each other. Typically when the aperture adjustment is stiff, the blades tend to bulge and when that happens thye get tangled with each other and ruined.

 

[shutterfinger]

Its currently wide open and stuck in its flange. The owner said he managed to work it there from partial stop down. Front and rear elements remove easily.
I'm well aware the blades buckle and break if forced.


And I got lucky
After removing the aperture ring set/index screw the aperture ring grudgingly unscrewed from the barrel. Once the ring was off spraying out the slot for the aperture range with CRC Quick Dry Electronic contact cleaner the aperture started moving freely but rough. I dried off the blades then wiped them down with extra fine powdered graphite making sure to get plenty into the pivot pin holes then shook out the excess. The aperture and center element appear to be held in place by a internal retaining ring that will not budge so I could not treat back side as I would like to.

 

[02Pilot]

Powdered graphite is excellent for smoothing the action of aperture blades - works well on shutter blades too, but I've found they need it less often than apertures. FWIW, I've had good luck applying a liquid cleaner and then the graphite powder while the blades are still wet. This seems to help carry the graphite into the less accessible areas without complete disassembly, which is sometimes unnecessarily difficult or in fact impossible.