One way or two way rotation with the Jobo?
I happened to be developing some film today, and I noted that the small white "gear" with three "blades" can be adjusted so that the expert tanks will rotate in one direction, or in two directions ( that is, will reverse after after a certain traverse ). Naturally I began to wonder when one would use one way rotation, and when one might use the back and forth rotation. I have been using the back and forth rotation with my expert tanks, but I am careful never to overload the tanks with too much solution....thus, I develop only a few sheets of film at one time. Can anyone speak to when "one way rotation" should be used? I did note that with the one way rotation the speed of the drum is not as easily adjusted, i.e., the rotation appears to be very much faster then I recall, and setting the speed dial does appear to have much affect.
Use the two way. It helps prevent any developing marks and makes agitation even.
Are you using the 4x5 drum or the 8x10 drum. No need to use a partial tank in my experience with the 4x5 tank. You should be careful to use two hands with the lift. I use my left hand on the lift and my right hand under the drum for support.
I am not aware of a useful purpose for the one way rotation.
I agree with jeroldharter. I always figured it was for future compatibility with some yet un-invented process that might require single-direction agitation. Either that or it is for use with their 'rock tumbler' conversion kit...
Thanks Jerold and ic...have you heard of anyone blowing out a motor on a CPP or CPA, and if so, what was the "cause" ? I would hate to have to give up the Jobo, and so I am very careful Jerold about the weight of the drums ( that is, the weight of the solution added to the drums which translates into the number of sheets developed! ).
No first-hand experience, but I did read reports on the forums of motors slowing or stopping. I believe there was a "motor upgrade" about 10 years ago, but I don't know much about it. (Serial # 22000 and lower?)
Originally Posted by Mahler_one
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Been there ...
If one experiences the failure of the tank rotation motor to turn, It is probably NOT due to motor failure. There is a rather strange triple-contact relay cammed by the shaft carrying the "three-lobed" reversing cam. The relay contacts there are not enclosed, and over time foreign crap works its way in there, effectively insulating one contact from another.
The cure is not easy. The control unit must be disassembled (top half pried - with great patience and care - breaking the sealing material from the bottom). Be sure to remove all necessary screws, fasteners and knobs. Follow the shaft to the relay assembly. It will be hard to see - access to it is a genuine challenge!!!
I suggest you have an assortment of extra-long straight and bent needle-nosed pliers, tweezers, and soft wire, for tool improvisation.
Once there it IS possible (have faith!) to work tiny strips of paper between the contacts to clean then.
I have performed this lttle exercise on my JOBO CPP-2 three times, successfully.
OBTW -- Jobo only advises one-way rotation when developing Kodak "Disc" film. Why? - I have NO idea.
Ed Sukach, FFP.
Originally Posted by ic-racer
What a great find!!! Apparently, if one's Jobo serial number is high enough, then the motor and everything "else" should be able to function with the same reliability as the ATL. Since I believe that the ATL is pre-programmed to rotate both ways (???) there should be no issues with undue wear on the Jobo CPP motor with bi-directional rotation as long as one has a unit with a high enough serial number!! MIne is over 24,000 so I am relieved. However, the real importance is if one is considering a used unit, and one uses expert tanks. then the serial number assumes tremendous importance. Ask for the serial number if buying a used CPP/CPA!
Ic....I really thank you for going to the effort of finding the information, and posting such.
Last edited by Mahler_one; 04-07-2009 at 04:52 PM. Click to view previous post history.
I only process sheet film with my Jobo and use one way only. No problems.
PRocess sheet film
Thanks....what drums to you use on which Jobo model?
Originally Posted by msage
In general, two-way is safer. It minimizes the possibility of standing flow patterns which might lead to uneven development.
I have a CPA-2 with a late serial number, but I'm still really wary of overloading the motor, especially since the machines are no longer being made. With the larger Expert drums (3004, 3005), which are pretty heavy even empty, I generally keep the fluid load to 600 ml or less.