Simple Jobo 2500 Rotary System

This system is intended for Rotary development using the Jobo 2500 tank. Note that the 1500 series will not fit, but you could build a similar system pretty easilly using the “tankhalten” and "rolle" files from the original model by Franktion, and my “Tank Holder Rear” model.

This build consists of 5 printed models:

• tank_holder: a stripped-down version of Franktions “Tankhalten” model. This piece holds the outside of the tank lid, and has dedicated holes to hold the aluminum rods

• tank_holder_rear: a stripped down version of Franktion's “tricther” model. This piece holds the inside of the tank lid

• rod_connector: A spacer that holds the aluminum rods the correct distance apart. Also doubles as an arm to keep the tank in place

• gear: unmodified from Franktion's model; spins the tank via the Jobo cog lid

• gear_cover: unmodified from Franktion's model; holds the gear in place at the end of the motor shaft

The system uses an off-the-shelf plastic tub to hold water, and a sous-vide to control the temperature for C-41 processing. For B&W processing you can obviously just use the rotary system with no water.

Disclaimer: use at your own risk! This system requires basic soldering skills, and involves electrical work, water, and of course, film processing. Be aware of the shock, burn, and other risks involved before taking this on. I am not responsible for any damage that happens to your or your film during the assembly and use of this tool.

I highly recommend using some practice rolls of C-41 to dial in the process. Do not, for example, attempt to develop your wedding photos as your first attempt at using this. 

 You will need:

• A sous-vide cooker to control the water temperature

• A 37mm 12v motor, such as this one from Amazon 

  • Note: I used the 15rpm model, which seems to work fine, but the Jobo CPE-3 system spins the tank much faster. I don't think the speed matters very much.

• A 12v power supply to drive the motor. I used this one.

• A tub. Any spare tub you have lying around will probably work, but I recommend using one with flat walls instead of tapered walls. I used this one.

• 8mm aluminum rods, or your choice of similar plastic or wood dowels. They must be longer than your tub's width. I used these rods. They are 12" long, and my tub is 11.8" wide,

• Minimum 2 skateboard bearings (size 608)

• Some machine screws (I used a mix of M3, M4 and M5 screws that I had on-hand)

• Water-proof epoxy, such as JB Weld. I used their "Super-weld" UV-curing resin because it is convenient.

• Jobo 1505 Cog Lid or equivalent. Frederik on Printables has a 3d printed version, but I used the official one for $30 on B&H

• Soldering iron, drill, and dremmel

• Optional: dust cap. I used this one form MrPaul. This will prevent any splashes of chemical from spilling out of the cog lid's open top

 Assembly Instructions:

• Attach the motor to the tank holder using M3 screws

• Using screws, attach the tank_holder_rear to the tank holder, and mount the gear and gear cover, as shown in the CAD images

• Using the rod connectors as guides, mark and drill holes on either side of the tub. The holes should fit snugly around the aluminum rods, but will not be water-tight (this will be fixed later using epoxy)

• Using a dremmel, file, or other tool of your choice, grind the inside of the bearings slightly so they fit around the aluminum rods

• Feed the rods through the holes in the tub, passing them through the three rod connectors, the bearings, and the tank holder, as shown in the images

• Press the tank holder against the wall of the tub, and use your choice of screw to secure the tank holder against the wall. In my case, I drilled two holes and used two M4 screws for this

• Position the bearings and rod connectors as pictured, so that the bearings hold up the red portion of the tank

• With the power supply disconnected, solder the motor to the power supply

• Connect the tank and run the motor. 

  • Note 1: the tank has a tendency to pop off the drive system. The third rod connector is used to prevent this. Since it is only attached to one rod, it can be rotated out of the way while attaching the tank, and then placed behind the tank to hold it on the tank_holder

  • Note 2: The rod connectors should be a friction fit on the rods. Loose enough that you can move them to position the bearing correctly, but snug enough that everything should be held in place. If this is not the case, consider gluing things into their place

  • Note 3: I actually snapped the small tube off the tank holder rear to allow me to install a cap on the tank, preventing spills

• If the test run worked well, and the tank rotates as expected, use the epoxy to seal all holes on the side of the tub

A Note on Motor Control

The assembly instructions glossed over the electrical setup. The bare minimum is soldering the power supply to the motor, so that whenever the power supply is plugged in, the motor is spinning. But there are many other ways to do it.

The Jobo CPE processors changes direction every few seconds. This is presumably to add some randomness to the motion of the chemicals, to avoid and streaking. For example, if there was a piece of debris on your film, spinning in one direction the entire time might cause a "wake" behind that debris (like a rock sticking out of a river), resulting in a streak in your image where there was less developer over the film.

I've used constant-direction agitation before and the results were fine, but when I built this tank, I installed a reversible switch that I can flip a few times during development to make the agitation a bit more random. My switch is quite close to the water line though, so if you choose to do this, try to find a better mounting location than what I did.

If you want a hands-off approach that doesn't require flipping a switch during development, MaDog541 has some schematics for an arduino-based timer in his MIFO semi-automatic prcoessor project. Amazon has a few 12V cycle-timers as well that seem promising. But if you are considering this approach, odds are you are better with electronics than I am, so I leave you to your own judgement.