This isn’t a new build, but a modification of an existing 8″x10″ print washer to handle 5×7 negatives. I made the washer about 10 years ago. While I wish I had done a few things differently it isn’t bad enough to start completely over.
About the original build: The tank panels were cut from 6mm acrylic (polycarbonate) sheets. The plumbing is captive, so it needs to be cut and dry fit before the tank is welded. The plumbing parts are solvent-glued together while assembling the tank.
The tank panels were cut and jointed with a pattern router bit to make sure the edges are square and true. That way the tank only needs to be held together with tape while joining the seams. I used Weld-On #4, which is a water-thin solvent that works by capillary draw, filling the joints of the clamped- together pieces and fusing them together.
The acrylic material used for this is not Lexan (despite the picture). I’ve forgotten the brand name, maybe it was Plexiglas. It’s slightly more rigid than Lexan, but also more shatter-prone. Not sure if Lexan would be better for the tank walls, it might deform more easily. Lexan can also be difficult to score and snap because it is so shatter-resistant.
Not that a print washer will shatter in use- it is mostly prone to cracking during machining. The 2.4mm sheets I used for the slot basket panels are especially tricky to drill when ganged together. The bit tends to wedge the swarf in between the sheets, causing them to crack unexpectedly. There are drill bits available for acrylic that may reduce this problem but I just made a plywood template to serve as a pattern for cutting each individual basket panel to exact size and for locating the holes. (The template in the photo above was just made to pattern-route the scallop along the top edge, the original template is gone.)
Since the basket panels are joined together with all-thread, and the tank itself has plumbing running through it, most of the holes have to pretty accurate. If all the panels are identical it’s simple to set up stop blocks on a drill press to locate the holes so they line up exactly, although alignment for the large circulation holes in the panels isn’t critical. They were drilled with a ~60mm HHS hole saw, which wasn’t ideal, it tended to chip the edges. A carbide-toothed hole saw would probably cut cleaner holes.
After parts are cut they were sanded with 150 grit to deburr the holes and edges. This also gives the panels a slight texture, which seems to reduce negatives sticking to them. I also sanded the tank walls. Not sure if this weakens the bond of the solvent weld, but it has held up for ten years. A larger tank would probably be safer to omit the sanding. But the solvent is very thin and runs easily, which spoils the surface of the pristine sheeting. Sanding does help ‘erase’ these solvent drips.
The pluming is a continuous loop of CPVC, which supplies the water to high and low ‘jets’ and also structurally reinforces the tank. I came up with this design to help reinforce a 16×20 version of this washer, but it’s probably overkill for such a small tank. Inside the tank are two 1/2″ pipe sections of pipe, 1/16″ holes for water delivery were drilled to line up with the spaces in the basket. Outside the tank is 3/4″ pipe and couplings which provides a seal against the tank walls. A reducing bushing connects to an elbow so there is a washer surface against both sides of the tank walls. They are seated in silicone against the Plexi to prevent leaks in the tank, but they joined to each other with CPVC solvent. The inlet side of the loop has a quick-release garden hose attachment to connect to water supply.
About the actual modification: I mostly just scalloped the top edges of the panels to make removing the negatives/prints easier. I also drilled a few additional holes to break each slot into two small compartments for 5×7 negatives, so now I can wash 20 negatives per. I drilled more holes for rod than I needed to- I’m out of stainless steel rod, and realized that simple strips of Lexan placed through the bigger holes would divide the basket just as well. They aren’t glued-in, the vertical one in the middle is friction fit, and the bottom strips just lay across the holes. The strips are kept in place by the walls of the tank and are easily removed when needed for washing 8×10 media.
Things that could be better:
- Inlet is on wrong side of tank for my current sink setup.
- Inlet riser is too low, needs to be higher than the highest water level of the tank or it will drain from the inlet when disconnected from hose.
- This is a wet sink tank only, I would like to make a siphon-style tank that can be used on a counter-top to save sink space. This tank is too short and needs to be filled to the brim to fully immerse the media. I always flip it upside down half-way during washing.
- The drain design could be better, need to manually dump the last 1/2″ of water. Also, not wild about how far the drain valve protrudes from the tank.
- My larger 11×14 version has a multitude of 9mm holes instead of the 60mm holes for water circulation. They are on a layout designed to allow for the insertion of stainless steel rods, which allows for the reduction of the slot size to suit whatever size print or negative I’m working with. I may eventually do the same with this smaller version.
There’s an updated version of the negative washer here: