I am recognizing there is some irony that has transpired while coming up with the mk2 design – mistakes were made. The mk2 design was suppose to be taking another stab at a printable laminar nozzle with many years of modelling / 3D printing experience combined with understandings of the laminar physics. But what actually resulted was another flawed design in many ways.

Not good

Body was long and skinny which translates to – not much volume in the exit chamber
Input source flows inline with exit – possibly allowing high-pressure in the middle, lower pressure on the edges
Narrowing towards the exit – creates a pressure differential prior to exit

I feel it is important to recognize and own up to my mistakes – then attempt to do better! Not all was bad in mk2 though –

Good

Square volumes that are well suited for FDM printing techniques
Side printing of the Straightener Stage so that water flows parallel to the layer lines
Diffuser Stage can be printed too! (less additional parts needed)
Interchangable lenses to aid with ease of prototyping / testing

Enter ✨ mk3 ✨!

This design tries to incorporate some things I have learned/observed from my previous designs, others published online and general theory.

More specifically --

Discrete stages
1. Chamber Entry – Allow for some settling before entry into stage Diffusion
2. Stage Diffusion – Kill / dampen turbulence induced from hose and entry
3. Stage Straightening – Induce laminar flow (R < 2300) via pipe diameter vs flow rate (see Reynolds Number)
4. Chamber Exit – Large chamber to transition from Straightening to Lens with uniform pressure
5. Lens (nozzle) – Shape / polish tuned to support column uniformity for “rod” like aesthetics
Prioritizing and encouraging the creation of uniform pressure
- Form factor – rather than long and skinny, we want short and fat
  - Straightener Stage width has been increased
  - Overall Straightener Stage length has been decreased, but over all Straightener Stage volume increased
- Exit transition
  - Less like a rocket nozzle that gradually tapers, more like a balloon with a hole in it (ie. an extruder)
    - No longer tapers towards the nozzle
    - More volume in pre-exit chamber
- Lenses (Nozzle)
  - A critical part when striving for “glass rod” like aesthetics
  - Shape, material, finish is important
  - Ability to iterate quickly and test different designs
    - No fastening with screws
    - Push-friction fit / hot-swappable
- Sideways input feed
  - Rather than feeding water in the same direction as the output, adopt a 90 deg / perpendicular approach
    - Less likely to create pressure differentials that can persist into the Straightener Stage

Tradeoffs

Complexity / form factor size has been increased a bit
Does not have a “all-in-one” version like mk2 (one may come in the future)

Execution of Concept

A clamshell design has been adopted so that
- Parts can be printed individually in strategic orientations (eg. Straightener Stage layer lines parallel to the flow of water)
- Different Stage designs can be easily swapped out / prototyped and tested for performance / function
Lens Holder
- Lenses can be hot-swapped without shutting water off
- Aid in ease of testing and prototyping
Stages
- Diffuser and Straightener as discrete parts that go to make up the whole
- Diffuser
  - Cross-hatch version
    - To be printed face down so that there are solid extrusions from end to end in the X/Y directions (Z as up)
  - Aligned version
    - Can be printed face down or on its side – as long as the filaments run side to side on a single layer
- Straightener
  - To be printed on its side so that layer lines run parallel with the flow of water

Cross-Section Diagram

Stages

Individually Printable Parts

Can be printed in any material unless otherwise specified, prototyped and tested using PETG

Base
Cap
Lens Holder
Lens Holder Gasket (TPU)
Stage - Diffuser
Stage - Straightener
Lens

Printing Notes

Stages
- Prints assume a 0.4mm nozzle, attempting to print them with other sizes may result in failed prints / lines not rendering
Base
- Pause the print to insert M3 square nuts (x8)
  - Layer 543 (137.7mm) printing with 0.25mm layer heights
STL's are already oriented in the axis that they should be printed

Assembly

Slide the Diffuser Stage into center chamber of the Base
Insert the Straightener Stage into the center chamber of the Base
Attach the Lens Holder to the Cap using M3-18mm screws (x4) and M3 hex nuts (x4)
Attach the Cap to the Base using M3-18mm screws (x8)
Slide a Lens into the Lens Holder
1. Be careful to ensure the Lens Gasket stays in place and is sandwiched between the Lens and Cap
(Optional) Increasing water seal where the lenses attach
- With no lens mounted – rub a little silicone sealant around the lens holder area and on the back of the lenses
  - Let cure for the amount designated on the instructions

Bill of Materials

Item	Quantity	Purpose
M3-18mm	8	Joins the Base and the Cap
M3 square nut	8	Insert into Base during print
M3-18mm	4	Joins the Lens Holder and Cap
M3 hex nut	4	Top of Lens Holder
Other Printable Parts	584g	A material of your choosing (tested in PETG)

Reference Links

Model origin

The author marked this model as their own original creation.

Laminar Flow Garden Hose Head (mk3)

Description

Versions

Note

Overview