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Re: Info On Jobo Drums

If only one tube were involved you would be correct a 180 degree or better
rotation would suffice. But since the drum that I am familiar with (3006)
has six "chambers" it is apparent that those which start out at  2:00, 4:00,
8:00 or 10:00 will either hit top center or bottom center with a 180 degree
rotation but not both. A 360 degree minimum rotation is required to have
each chamber see the same conditions as the others.

Wayne

----- Original Message -----
From: "Sandy King" <sanking@hubcap.clemson.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, October 30, 2000 9:31 PM
Subject: 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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