Modular Stream Table

I recently visited the small Great Lakes Children's Museum in Traverse City, Michigan with my daughter. They had a simple and elegant installation made by Tom Egan that captivated all the kids and adults there. I've always geeked out over stream/erosion tables but they are messy and the physics involved just aren't as effective or satisfying at reasonable household tabletop-scale. So, as soon as I we got home from our trip I started working on this modular printable stream table and set of accessories designed to let anyone live out their civil engineering or fluvial geomorphologist fantasy. 🤓

If you've read this far and just want to get started, this is the pump I picked and I use two of them in my setup. As a bonafide 5W pump, it moves more water than any of the other USB-powered options out there and as a bonus it has an actual digital speed controller instead of just a physical slider to change the flow rate. If it wasn't obvious, I stuck with a USB-powered pump for safety reasons and I run them from a battery pack, not an AC adapter. Just say no to playing with mains power and water, ok?

I used a Sterilite 32 quart/24" tote as the sump but anything watertight and big enough to fit the table inside of will work. I considered making the entire thing self-contained, but I didn't want anyone to have to worry about leakage and the project would have lost some of its simplicity if it required that caliber of assembly (not to mention water-tightness of the print itself). Plus, you can just dump out all the water and store the entire thing in the tote when it's not being used!

That's all the critical information for you fast starters, go off and print and try to remember to post a make if you put one together. 👍

For anyone still reading, I have some additional details to share. If you've looked at the model, you make have noticed a non-traditional method of joining the three main parts together. I have to say that I'm really happy with how it worked out. The half-washers that hold the outside sections to the middle are themselves held in place by the braces on the legs that align as you screw them in. It does mean there are left and right legs for the middle section, but they print with an L and R on them (which apply when the table is upside down with the downstream end facing you).

This thing was designed to max out the print bed of my Prusa Mini, something I try to avoid due to warping, but I really wanted it to be as large as possible so it had to be done. Thankfully, the thin outside walls and base mean that I didn't have much trouble with warping and the spilt-thread half-washer trick worked fine even with the little I had (I built in a little tolerance and the slightly sagging bridges fill the gap/provide pressure nicely). If you are worried, adding a brim should help hold down the bridged-over areas in the corners that have the highest chance to lift up.

While I didn't glue the pieces together, and a little leaking on the seams may be acceptable to you, I did put a tiny bead of silicone on both seams in mine and smoothed it out with a gloved finger. This isn't load-bearing silicone of course, and it doesn't stick particularly well to PLA, but it does stop water well enough that I don't lose any through the gaps. 😁

Still here? Alright, I appreciate that, here's the last chunk of details and some closing ramblings…

A decent amount of thought when into the overall scale of this project but a lot of it just sort of came together naturally based on constraints. For example, the 180mm bed on my Prusa Mini can only be divided into whole numbers of a reasonable size so many times, I ended up picking five instead of four or six, for example, because four didn't seem complex enough and six seemed too small, plus I wanted an odd number so there would be a middle channel. That said, the sides and support pillars occupy space, so my 180mm/5=36mm square became a 30mm x 26.068mm “square” at the end of the day. I wouldn't scale this design down, but since it fits on a 180mm bed, I don't think many people will need to. That said, it should scale up well and not be too hard to remix at the same scale for larger beds to make wider and/or longer streams. You could also simply stack the output of one above the input of another if you had a long enough sump.

I tried to design a good starting set of the slot-in pieces. They each have a purpose to discover. You can have a lot of fun with just the basic “square” and rectangle, but I wanted some other options to allow for more complex (and colorful) systems to be created, different ways to constrict and expand the flow of the water, etc… The moving parts, including the silly boats are good for visualizing the flow (or stagnation). If anyone is struggling or frustrated that something isn't working how they want, that's just part of the learning process. Moving a single piece can make huge difference and it's awesome to watch someone who didn't find it intuitive at first figure it out. I intend to add more pieces over time and I hope others contribute as well.

You can print the entire main table assembly with a single spool of filament at default PrusaSlicer settings. What else you print is up to you, but whatever color scheme you go with, consider printing the slot-in pieces of the same type in the same color for easy identification. It's a great way to use up scraps since they are so small. 👍

If you print the turbine pieces, some assembly is required. I did design a spinning print-in-place turbine first, but physics was not its friend and it was destined to fail. So, I changed it to print in three pieces and be glued to a 1mm shaft. I had brass rod laying around, but use what you've got that is straight, you might not even need glue if it fits tight enough, it doesn't have to be very strong. My method was to stack all three pieces on the rod with the rod sticking out just slightly on both ends, then dab a little CA glue on there to lock the pieces to the rod while keeping the glue as far away from the center as possible so it wouldn't gum it up. Do leave a thin gap, though. I also made sure the print bed-side of the “tail” and “housing” faced each other when assembled since they are the smoothest and in contact when it spins (it will only spin when the tail is facing into the water flow). 

Depending on your printer, you'll probably need to drill out some of the small holes in the model, specifically the turbine pieces mentioned above and the water wheels and flaps. I love this cheap precision drill set for that kind of work.

Speaking of the flap pieces, while the entire stream table is kind of like baby's first Phillips Machine, the flap pieces are particularly satisfying to use for simplified fluidics. It's actually shocking how precise/granular the systems can be. In the the image below, flipping the purple piece with the arrow next to it would reliably swap which of the two turbines with arrows next to them spun. 🤯

I've had some fun introducing bubbles into the water using an airstone and an aquarium pump, it further helps to visualize the flow. If you are tempted to add soap, use dish soap and use the tiniest amount you can possibly squeeze from the bottle at once or the bubbles will take over everything. If you are tempted to add food coloring, I hope you don't stain anything. That said, Airsoft BBs have been popular as well, just keep in mind that anything moving through the water besides water is likely to mess with the moving parts you may have in the system.

Finally, there are some extra details in the notes section of each file, don't miss them.

Have fun!