Make your own 4x5 developing tanks

These tanks are reasonably easy to make and seem to give really even development. The basic idea is pretty simple - you have a carrier with curved slots in it that holds the film sheets, there are a bunch of tanks for processing and a lid which fits over a tank (with enough headroom for the film carrier). It isn't a "daylight" system - you have to do most of the processing in the dark - but if you make sure the lid is light-tight you can turn on the room light between agitations.

Figure 1: The film carrier, developer tank and the lid.

Figure 2: The whole system, with 2 sheets of film in the carrier.

The tanks and the lid are made of 4.5mm PVC and glued together with PVC solvent glue that plumbers use for assembling PVC pipes. The film carrier slots are made of 3mm PVC. The colour coding is just gaff tape.

The most fiddly component is the film carrier. You can see most of the salient features in the photos above, including the all-important retaining bar at the bottom of the carrier. It's a thin strip of PVC at the bottom of the carrier that stops the sheets falling through. It runs down the middle of the opening, perpendicular to the film sheets.

The curved slots are important: If they're not curved the film tends to flop around in the chemistry and can come adrift or touch other sheets. This system holds the film really securely - I've never had a failure with it. The hard part is making the slots. I made up a simple jig for my jigsaw that let me swing it in an arc of radius 150mm or so. Using that I cut curved slots into a piece of 3mm thick PVC to form a sort of comb-looking thing. In other words, the curved "fingers" remained attached at the far end of the cuts. I cleaned up the cuts with some sandpaper, then glued the two comb-looking things to the unassembled inside faces of the non-handle sides of the carrier. After the glue had set I cut off the "body" of the comb, leaving the fingers glued neatly to the sides.

I also filed notches into the top of each tank - one notch for the dev tank, two notches for the stop bath tank, three for fixer and so on. This is quite handy if you ever mix up the tanks in the dark. It's probably worth gluing some feet onto the tanks too so that they don't stick to your darkroom sink when it's wet.

I use these for B&W processing (TMX in TMAX RS usually, but also various films in Ilford Plus), and the development is even and consistent. With the lights off I load the carrier, drop it in the empty wash tank, and then put the lid on it. I then turn on the room light and get all the chemistry ready. For timing, I play an audio timing track, which is just a recording of me announcing the time and other instructions (e.g. "Timing tape for film X in developer Y. Time starts in thirty seconds ... Time starts now ... Thirty seconds ... One minute ... One minute thirty seconds ... ... ... Seven minutes, thirty seconds ... Development stops in ten seconds ... Development stops, Stop bath starts in ten seconds ...." and so on). At the moment, this is still on cassette (which is surprisingly accurate - within 5 seconds over 8 minutes), but it would be much better as a track on an MP3 player. As a backup I have an electronic timer that also counts down the time and then beeps, so if something goes awry with the tape I can probably estimate the agitations and still get a good result.

With the lights out I start the tape, and when it says go, I lower the carrier into the developer. I agitate it by raising it, tilting to one side, lowering, raising again and tilting to the other side over about a 10 second interval. I do all the dev and stop bath in the dark, and after about 3 minutes in the fixer I turn on the light. Wash, ridfix and photo-flow in room light.

Construction details

• All dimensions in mm.
• Material is sheet PVC
• You'll need a jigsaw, clamps, PVC solvent glue, saw for cutting PVC (or get a shop to cut the pieces to size), sandpaper, maybe double-sided tape, some plywood and MDF or similar to make the jig for cutting the curved slots.
• Don't sue me. I think the instructions are complete, and the dimensions right, but I may have got something wrong. Do this with your brain switched on and let me know if something is wrong or unclear.
  

Film carrier
	qty	thickness	height	width
sides	2	4.5	168	110
front, back	2	4.5	128	93.5
film guides	2	3	180*	180*
film retainer bar	1	3	8	93.5
Tanks (total of 5)
	qty	thickness	height	width
sides	10	4.5	148	123
front, back	10	4.5	148	107.5
bottom	5	4.5	127.5	134
Lid
	qty	thickness	height	width
sides	2	4.5	174.5	134
front, back	2	4.5	174.5	118.5
top	1	4.5	125	118.5

*The sheets that become the film guides need to be a fair bit bigger than their final size so that the slots can be cut into them easily. They finish up having the same dimensions as the front and back of the film carrier.

Making the tanks and lid

Just glue them together as shown in the drawings. Make sure you get the edges and faces right or things won't work. Do a dry run first, holding everything together with tape. When the glue sets, sand off any rough bits and sharp corners, File notches in the top of the tanks so you can tell them apart in the dark, and colour code them with tape. Test them for waterproofness and light-tightness. Any light leaks can be fixed with gaf tape or more solvent glue.

Making the film carrier.

First you'll need to make a jig for your jigsaw that lets you swing it in an arc.  I used a radius of 136mm. See the drawings. I bolted the jigsaw to the jig arm, but you could probably use double-sided tape instead. To make the guides you cut 8 curved slots into the 180x180 sheets, with a distance of 8mm between each cut (my original model has 10 slots, but the last 2 are unusable because the handle is in the way).  Use a jigsaw blade that leaves about a 1mm cut. The cuts need to extend the entire height of the film carrier (128mm), and you probably want to make them a mm or two  longer just to be sure. The center of curvature has to be about halfway down the film carrier too, so align the sheet on the jig so the pivot point of the arm is about 60mm up from the bottom edge of the sheet. Clamp the sheet to the jig baseboard, and move it along 8mm for each cut. Clean up the cuts with sandpaper. The film has to slide easily through these slots.

Once you've cut the "combs", glue them to the front and back pieces of the film carrier so that the front and back form a symmetrical pair that you can feed sheets of film into from the top. Note that the rightmost slot in the diagarms is not hard up against the edge of the front face - there has to be enough space so that you can get a sheet of film past the handle and into the rightmost slot. When the glue dries, cut off the pieces of the combs that lie outside the edges of the front and back pieces they're glued to. Clean out any excess glue and any remaining rough edges from the slots with sandpaper. You can now cut a fancy handle into the top of the film carrier sides if you want (see photo), or maybe just drill a big hole through the top of each so you have something to hold on to easily.

The final tricky part is getting the distance between the front and back just right so that film fits snugly between them - not too tight, or it will be hard to insert the film, and not too loose or you risk the film popping out during agitations. To do this, get some scrap sheets of film to use as spacers. Glue the sides to the edges of the front and back pieces and while the glue is still wet, insert the sheets into the slots as you would for processing. Adjust the front-back depth so that the sheets slide in and out OK, and leave it to dry. You probably have a few minutes to adjust this before the glue gets too viscous to allow further adjustment. When the glue is completely dry, take the sheets out and check that they still slide in and out smoothly. You can probably deepen the slots with some sandpaper if they bind a bit.

All you need now is something to stop the film falling right through the bottom of the carrier. Glue the retainer bar betwwen the two sides at the very bottom of the carrier as shown. Thats it!