Pour Over Coffee Bot: Dispenser Design

In my last post I mocked up a rough outline of my 2-axis gimbal design – let’s now dive into the details of designing the first component: the Dispenser.

2-Axis Gimbal Diagram

The primary deciding factor for the design of the dispenser is the tubing used for all of our water flow. After a bit of research I landed on this High-Temperature, Food-Grade, Silicone Rubber Tubing from McMaster-Carr ($0.88 per foot). I picked a tube diameter that closely matches the spout on my pour-over kettle at home – 1/4″ OD, 1/8″ ID.

I’d like the dispenser to consist of two parts that fasten together around the tubing. I’ll be periodically assembling / disassembling the dispenser, so I’m going to rely on machine screws for all of the fastening  – hooray no fussy snap fits!

Dispenser Assembly1_4.gif

The design utilizes M3 Brass Threaded Inserts from McMaster-Carr ($0.21 each), which find their way into almost every project of mine nowadays. The inserts can be pressed in place with a soldering iron to melt the surrounding plastic and ensure a secure fit. It’s also incredibly satisfying to watch.

The dispenser will also need to mount to the Micro Servo horn, and I always prefer using machine screws for this, as well. M1.6 seem to be the perfect size. Hand-Tapping the holes on standard servo horns is a breeze, and your future projects will thank you.


The servo-side of the dispenser body has counterbored holes for the M1.6 machine screws, and you can see the assembly process above. The bearing-side of the dispenser has a feature that fits into a standard 608 bearing ($1.18 each).

The dispenser parts will be 3D printed, neither of which require support material. I’m planning to use PLA for this build, so I’m slightly concerned with the heat from the hot water softening the plastic. I’m thinking some heat shielding tape ($0.63 per foot) around the tubing should help insulate the tube and prevent any glass transition of the PLA. Key word: should.

Done with the dispenser!

Next Step: Complete gimbal assembly



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