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Re: Info On Jobo Drums
I Need to read better. You are stating a bi-directional 0.6 turn in each
direction from center (I didn't get that from the original poster's
comment - but of course it must be correct). This would allow all chambers
to see every condition but not for the same period. Some chambers would see
two drains per cycle while others would see only one. With the change in the
laminar layer that this would afford those tubes which "break the surface"
vs. those which don't it would still lead to different development for
individual sheets and (only an opinion) possible uneven development on the
sheets which "partially" break the surface.
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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