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Re: Info On Jobo Drums

But I don't understand what you mean by full coverage. Perhaps my 
misunderstanding of how the Jobo drum works is wrong? I had assumed 
that an exchange of solution was continuously taking place in each 
tube as it passed through the lowest point of rotation, and that the 
tubes drained solution back to the bottom up to and through the high 
point. If that were the case it would appear that the only critical 
aspect of the rotation is that each individual tube pass in 
alternating rotations (one turn, then reversal)  through these two 
points, high and low. That would be achieved with a reversing 
rotation pattern of 0.6 turn in each direction.

Perhaps my assumption is wrong about the way multi-tube Jobo drums 
work, or maybe the logic is off?

Sandy King







>If you don't exceed 360 degrees of rotation you don't get full coverage of
>the film.
>
>----- Original Message -----
>From: "Sandy King" <sanking@hubcap.clemson.edu>
>To: <alt-photo-process-l@sask.usask.ca>
>Sent: Monday, October 30, 2000 8:27 PM
>Subject: Re: Info On Jobo Drums
>
>
>  > Peter,
>  >
>  > I have been trying to figure out why a rotation sequence that only
>  > turns the drum 0.6 - 0.7 of a rotation is a problem. There must be
>  > simple answer that escapes me  but my first thought is that as long
>  > as each of the individual tubes can empty out/fill up again the total
>  > amount of solution would be in a constant mix and the agitation
>  > pattern would be even. What have I missed?
>  >
>  > Sandy
>  >
>  >
>  >
>  >
>  > >Sandy:
>  > >
>  > >I use the 5-sheet Expert drum for my 10x8's on  a Jobo CPP
>  > >processor. I tried to use a Unicolor roller base before I got the
>  > >CPP, and found that the rotation sequence only turned the drum about
>  > >0.6-0.7 of a rotation. I was in the process of modifying the timing
>  > >sequence but gave up when I got the CPP. Modification required
>  > >building a switched relay unit using a 555 timer, transformer, etc,
>  > >and was proving to be something of a pain.
>  > >
>  > >I also had problems with anti-halation when I used a Jobo print drum
>  > >to do my 10x8's, but have not had any at all since using the 3005
>  > >(and I have a two sheet Expert drum for 10x8's as well, which
>  > >wouldn't work for smaller film sizes, I suspect).
>  > >
>  > >The one thing I didn't realise about the 5-sheet drum initially is
>  > >that the drum actually has holes in the bottom to allow water from
>  > >the tempered bath to fill up the space around the film slots to
>  > >maintain solution temperature. The drum is quite heavy when lifting
>  > >it to dump chemicals.
>  > >
>  > >Cheers
>  > >
>  > >Peter.
>  > >
>  > >
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