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Negative washer

I’ve been in a creative slump, so why not make a new washer to wash all that film I’m not shooting?

My current negative washer was converted from a 8×10 print washer. It’s pretty oversized. I had a large piece of .25″ cast acrylic on hand. It’s scratched and scuffed to all hell, so I hit it with a random orbit sander to give it sort of a frosted look. Good enough to try out a different design.

Cutting acrylic can be a little violent without the right saw blade. Standard triple-chip grind blades work ok but chip out quite a lot. Standard woodworking blades tend to melt polycarbonate sheeting- enough to need a respirator or really good ventilation when cutting.

To get a good edge for solvent welding, it helps to pattern-route the pieces against a straight edge using a bearing bit. Suffice to say this is extremely time-consuming. Trying to keep everything properly sized and square while pattern routing each edge is a fairly huge pain in the ass. I should just get a better blade, the time saved on just one such project would be worth the expense. The 12 negative slots (.125″ x .125″) were made in .25″ acrylic sheeting using a crosscut blade on a tablesaw. It also chipped a little, but was much better than the cuts. I smoother the edges of each slot with a triangle file. The false bottom for the negatives to sit on was joined to the sides with a stepped dado.

That ghostly CPVC pipe hiding below the basket was an idea I abandoned- the pipe loop was to be riddled with a bunch of pin-hole water jets. Low flow and diffusion works as well if not better than high flow agitation, so I decided on a single 1/4″ NPT inlet for water.  One side of the wash tank is shorter than the other, so water will enter from a inlet tapped into the bottom of the wash tank,  then spill over the top into a separate drain tank.

Drilling fill/drain holes in the false bottom with a center bit. The rabbet on each edge was cut on the router table.

Cutting the parts to exact size was tricky. Solvent welding wont fill gaps or work on loose fitting joints, so the parts have to be just right. I cut them to rough size on the table and/or chop saw, then pattern-routed them with a bearing bit against a straight edge. Using a fence helped to ensure all the negative channels aligned. Pieces unable to be clamped can be cleaned up on a makeshift jointer fence setup on the router table.

Dry fit. Another frustrating issue with the scrap acrylic I used was that the pieces were all slightly bowed or warped corner to corner. I used blocks to help even up the clamping pressure. I doubled up the back (right side) since I wasn’t sure if the film channels had overly weakened the acrylic. The wash chamber is only 5″ x 8.5″ x 10″ (a little over 1/4 of a cubic foot, holding roughly 2 gallons or 16 lbs of water), but what the hell. For the other side, I made a removable brace from scrap acrylic to fit between the two panels. I’m not not even done yet and I already want to rebuild this in more suitable material.

Before welding together with Weld-On #4, I drilled all inlets and drains and tapped the holes to accept 1/4″ NPT fittings. I went shopping for parts before I had a coherent plan and got way more fittings than needed.  I only ended up using one nipple, one 3/8″ barb 1/4″ FNPT elbow, one 3/8″ barb 1/4″ NPSM bulkhead fitting, 3 #9 O-rings, and two male 1/4″ NPT Loc-line valves. [I’ll be using this in the sink, but it’s suitable for use out of the sink, I would just need to replace the valves at the tank with extra barbed bulkhead fittings, and attach the valves to the end of the drain hoses with some barbed FNPT fittings or just use some pinch valves.] For the 3/8 hose hookup, I used a 3/8″ ID Hose x Swivel FGHT connected to a quick-release garden hose connector. I stuck with nylon fittings- I figured they would be the least likely to crack the acrylic if there was too much thermal expansion/contraction in the panels. The hose works well with the barbed fittings, easy to assemble and no clamps are needed.

I waited to weld on the outside panel of the drain chamber until I could test the inner wash chamber for leaks, there would be no way to reach that for touch-ups after it was completely assembled. I used clamps to reinforce the tank since the weld hadn’t yet cured completely.

The acrylic brace inside the drain tank is only a temporary support until the joints cure more. It can take 4 or so days to reach 80% strength. The drain on the right is to control the flow rate. The drain on left is to empty the main tank. It’s not really needed though- once disconnected from the water supply, the hose itself could also be used to drain that side. I should have added an overflow drain to the top of the drain tank, to protect against overflowing when used our of the sink…

This turned out well, so I ordered some clear acrylic to rebuild this with. All my negative and print washers are made out of the same batch of surplus ‘frosted’ acrylic, and I’m pretty tired of the stuff.

August 16th

I started on the new version. Only a few minor changes, I’m using 7/16″ stock for the wash tank now, and will stick with 1/4″ stock for the other outside walls and base. The overall size of the unit will be slightly smaller as well.

The material comes covered in a durable plastic-lined paper cover, which makes protecting the surface during fabrication a whole lot easier- especially cutting the grooves. I  got a new blade for the table saw, an aluminum triple-chip grind blade that’s also rated for plastics. Not perfect, but the cuts look better right off the saw than the cuts that I had cleaned up with a router on the first version. The trick seems to be getting the feed rate just right. The first few cuts I made were too fast- I thought it would help prevent melting, but a surprisingly slow rate worked better. None of the panels from McMaster were perfectly square so I got a lot of practice.

I was able to cut and fit up all the pieces in about an hour- the pattern routing on the first version had taken all day. Still, before any seam welding is done, I’m sanding out the faint saw marks and then flame-polishing the edges with a Mapp gas torch.

The drain holes were a bit more work this time around, I had to drill from both sides due to the increased thickness of the material.

 

I made a leveling base out of acrylic scraps. My sink slopes in two directions and I was tired of using loose plastic shims under the washing tanks in the sink. Just a piece of 1/4″ acrylic sheet with two tapered runners made from scraps of 7/16″ acrylic.

It was nice trying out a different design on free materials before using the expensive stuff. Having one side of the wash tank than lower than the other makes the loading the negatives in the slots easy, and the slots are deep enough that the negatives don’t pop out even when the faucet is wide open. The thicker acrylic doesn’t flex at all when full.  I like the drain tank as well, it gives a nice visual of the flow rate- the narrow tank will quickly fill up if the flow rate is too high.