Spirographic Planetary Gearbox - WDT Espresso Tool
Spirographic Planetary Gearbox - WDT Espresso Tool
Embedded Files
WDT Tools are commonly used when making espresso because they help ensure a more uniform extraction, leading to a more consistent shot and hopefully a better tasting cup of espresso.
WDT stands for Weiss Distribution Technique, and the tools have a large range of forms, but for the most part, it will have a few, very thin needles that allow the user to comb through a bed of ground coffee, breaking up any clumps, before tamping the coffee and pulling a shot of espresso.
The idea behind my design is that it makes WDT exceptionally consistent, thorough, and quick. I made 2 versions of this design: one for a 58mm diameter espresso basket and one for a 54 mm diameter basket, because my end goal was to not only make one for myself, but also gift one to my friend who got me into making espresso.
Exploded View
See It In Action!
The exploded design illustrates 5 unique gears all encased by a ring gear. The gears are all different sizes to ensure the path each needle follows is different in each rotation. This is the key to the design, making the gearbox spirographic as each needle is its own spirograph, creating a unique, continuously varying spiral.
These types of gears are known as herringbone gears, because of their helical chevron teeth. Not only do these gears have a structural advantage to regular gears, but they also ensure the gears can't fall out. The unique shape of the gears don't allow for the gearbox to be taken apart, but also makes the gearbox impossible to assemble. This means all the gears must be manufactured in place.
The knurled pattern, on the outside of the gearbox, helps to improve the grip on the gearbox when using it to distribute ground coffee.
Prototypes and Iterations
Technical Design Details
These gears are entirely equation driven, only needing the following inputs:
Pitch
Number of Teeth
Pressure Angle
Thickness
The gear teeth are defined with parametric equations, not using the commonly simplified definition with parabolic arcs.
The WDT tool has 2 different needle heights, to ensure that clumps of ground coffee are being broken up near the top and bottom of the bed. The 2 heights were determined from the distance between the gears and the bottom of the espresso puck, achieving approximately 80% and 30% of depth into the espresso puck.
Knurling details are below. The knurling pattern not only helps with the grip on the tool, but also helps to hide layer lines, an artifact of 3D additive manufacturing.
Sources and Resources Used
Sources and Resources Used
Yang Cao - ENGR 380 - Equation Driven Involute Spur Gear Design
Helix Twist Equation
Thread Design
Page updated
Google Sites
Report abuse