The primary design criterion for this week's project was to create a part that could not be made via subtractive manufacturing. I wanted to create a part with internal cavities, and I also wanted to re-establish dominance over my awful dishwasher. Therefore, I created a clean/dirty dishwasher magnet reminiscent of a stripper pen.
The exterior of the magnet is a flat surface without visible markings. Thirty thou below the surface are the fluid chambers in the shape of the words "Clean" and "Dirty". A dark fluid occupies half of the available volume, making only the chosen status indicator visible.
This job was run on the Object Eden with VeroWhite and SUP707 soluble support material. FDM-style printers would not be able to provide a water-tight finish, and would have difficulty with the overhung cavity ceiling. It fills the cavity with a temporary material during printing, allowing more difficult geometries to be rendered.
Six slots / vents were added for cleaning out this support material. The support dissolves in an ultrasonic soap bath, but this is rate limited by available surface area and fluid exchange. Rather than wait forever on the soap bath, cleaning became a 3 step process:
Water Pick / Spray Booth
Cleaned Part in Booth
When using the water pick, watch the color of the fluid leaving the site. When it runs clear it is no longer removing material. It was difficult to hold nozzle against the vent slots; a small misalignment would torque the part further away. Chamfering the slots may make this part easier.
The vent slots ruin the "water tight" aspect of the design. I used a gap-filling epoxy that is meant for sealing in a wet environment: Royal Adhesive's Double/Bubble Gap Filling Adhesive
Just before Sealing
Gap-Filler mixed in small bowl
5 Vents filled and resting
Close-up of cured vent plug
In a future iteration I'd instead plug the vents with printed material and then epoxy the smaller area.
A small magnet holds the part to the dishwasher, and is responsible for half of the name "Dishwasher Magnet". This part is press fit into the back. The hole was intended as an interference fit, but when it was printed it ended up nearly 10 mil narrower than designed. A deburring tool and some love from a rubber mallet rectified this. A future revision will have a more pronounced chamfer to aid in insertion.
Close-up of press-fit magnet
The magnet is now almost functional. It is water tight save for the single remaining vent. It sticks to things. It is beautiful. The one remaining task is to fill it half way with a fluid that:
#3 is where everything went horribly wrong.
Initial tests showed that water took too long to clear from the upper cavity. The font choice was too narrow, and surface tension held stubborn droplets.
I then tried Olive Oil. The oil did slightly better with surface tension, but it wasn't quite visible through the plastic. I wanted a more pronounced effect, so I added food coloring to the Olive Oil. Olive Oil hates food coloring. VeroWhite LOVES food coloring. The part is now stained so that the upper text is still visible.
I'd like to try to clean out the dye better. I spent about an hour attempting to manually flush it, but it is difficult to access the affected surfaces with 5 of the 6 vents plugged with gap filler. The next attempt will be to put it back in the ultra-sonic bath. Failing that, I'll reprint it with the following modifications: