KohiWerks ModGrind (Universal & Modular Motorizer for Hand Coffee Grinders)

(What is the ModGrind Project?)

The KohiWerks ModGrind motorizer project is an open-source motorizer project

I aimed to spark a new open source revolution within the coffee community in the space of motorizing hand coffee grinders for all coffee enthusiasts (and all for free!)

Like how RepRap was to 3D printing, i wanted to build a simple and efficiently designed hand grinder motorizing platform that can be built upon and remixed 

It's almost as simple as playing with legos

Feel free to edit/tweak my design and expand upon it as long as there's clear credit for it on the upload

If you really enjoyed/appreciated this design, feel free to tip me on Ko-Fi/PayPal! (soon)

This project aims to deliver a motorizer that delivers on several goals

• Easy to Build

  • A highly simplified design only requiring a minimum of 8 printed parts to build the chassis

  • It's easiest to build when using cylindrical shaped motors

  • Only 4 different lengths of M5 screws and one 2020 Aluminium Profile to build the chassis (if using cylindrical shaped motors)

  • Only requires measurement of hand grinder and cylindrical motor body diameters to edit centered holes into their respective mounting sleeve templates 

  • Every component bolts on or snaps/clicks into place easily

  • All wiring requires no soldering (when WAGO wiring clips are used)

• Highly Accessible

  • It only uses a combination of common generic hardware store parts and printed parts with the flexibility to use any motor, switches, power connectors and hand grinders to ones own individual preference

• Extreme Compatibility and Unlimited Customization

  • Able to use any motor configuration

    • Any type of motor... Brushless DC, Brushed DC, Stepper, Servo and ETC

    • There are multiple housings you can customize and edit to fit the electronic components you've chosen) 

    • The blank template files for the Mounting Blocks are easily customizable to mount any motor

    • Cylindrical Shaped Motors up to 60mm in diameter are supported with an easier to use pre-made template for cylindrical motors (Clamp Style Mounting)

  • Able to use any electronic parts/components (Any power input connectors, ON/OFF switches, controllers and ETC to one's own desires)

    • Multiple user editable electronics housings are provided as blank template files for you to mount any controller, switches and input connectors of your choice

  • Able to use any hand grinder

    • Up to 65mm in body diameter (and eventually larger ones)

    • Compatible with any shape and size grinder shaft (Most hand grinders use 1/4 inch hex) but any socket extension bit can be used to adapt other grinders 

    • Rare hand grinders that grind in reverse (Anti-Clockwise) are supported also

• Endlessly Accessorizable 

  • The motorizer is designed with very simple physical shapes and with multiple attachment points for components in an overall simplified format to allow for as much modularity and customization flexibility as possible 

  • The usage of an aluminium profile allows for extra accessories to mount to the motorizers body

• Open Source and User Editable

  • The design is built from the ground up to be a potent blank canvas for tinkering from its extremely simplistic and straightforward design

  • The use of an aluminium profile makes it highly customizable with endless accessories one can think of building/attaching to it 

  • I highly encourage everyone to build this and tweak and play around with the design and credit me and my Printables and socials 

• Great user experience

  • Hotswap your grinders and even motors in less than 10 seconds maximum entirely by hand

  • Seamless and easy bean loading 

    • Slide out to unlock the chute.... drop your beans.... then slide it back shut... and grind away...

• Safe for your hand grinder

  • The printed sleeves/jaws are designed to not to allow excessive amounts of compression forces on the grinder body

  • The printed sleeves/jaws are unable to scratch your hand grinder body

  • In the event the motor shaft, couplers and hex socket experiences misalignment, the design has built in tolerances to allow some freedom of movement to avoid sideways stress on the grinder shaft

(Current Revision Status)

This is still a work in progress and is currently undergoing some final functional performance tweaks 

If you're interested in the history and previous iterations you can find the previous builds and prototypes in the Makes section to see my changelog/devnotes

The current revision is Revision 11 

The old twist-lock barrel with circular sleeves tightened on the grinder body is now removed and archived as i no longer recommend using it and it is now replaced with my jaws 

(What updates am i currently working on?)

Alongside working on these features

• Tweaks to existing parts

  • For the clamp jaws, i will be redesigning it in Revision 12 with V-slots as part of its shape so that the 150mm Stainless Rods are no longer required to build the jaws to save my users the material costs and to make construction easier

• A new set of accessories

  • Universal Spring Loaded Retention Knockers 

  • Universal Anti-Static Ionizers 

  • Slow Feeder Adapters (to mount most of the popular slow feeders on the market to the ModGrind)

• A very big groundbreaking update (Flat Burr Modules)

  • This project was always meant to be an all encompassing full fledged modular electric grinder despite the project being disguised as a hand grinder motorizer project in the beginning phases

  • I am designing standalone flat burr grinding chambers with the same fundamental design principles as a hand grinder (central shafts and bearings, grind adjustment mechanisms and etc) to be mounted onto and driven by the ModGrind Motorizer 

  • The first few chambers will be designed in the three most common sizes starting from 64mm followed by 83mm and 98mm

  • This is designed to run on motors delivering high RPM and torque 

Some updates i am currently debating on making are

• Filming an assembly video as a more intuitive and easier to understand guide since written instructions are quite lengthy

• New additional XL sized clamping jaws for grinders larger than 65mm (up to 80mm diameter)

• New additional XL sized hopper and motor mounting blocks for larger motors 

• Adding an additional "Thick Base" as a user editable template file where you can mount your power inputs, controllers and switches to the base instead for certain types of builds (steppers, etc)

(Documentation and Build Guide)

This guide will help you get familiar with how the motorizer is constructed and will guide you along with figuring out what you need to do based on the build configuration you have chosen

We will begin by explaining the motorizers construction before getting to the build guide to serve as context to the instructions

The first thing to do when building your motorizer is deciding on your build configuration and there are multiple factors explained below that will determine the exact partslist and steps necessary to your exact build

(Choosing your motor and electronics)

The motor you pick will determine which mounting blocks you can use, the supporting electronics required and the electronics housings used 

Form factor and mounting

When using a cylindrically shaped motor, you can use the easiest option of the clamp style mounting blocks

But i highly recommend avoiding this method for extremely heavy loads like grinding light roasts as espresso for example due to the chance of the motor slipping in the sleeve and bolting the motor down with the 

For other motor shapes and form factors the blank blocks are necessary (and i still highly recommend using this even with cylindrical motors)

Motor Type and Electronics

The easiest motor to wire up is a brushed DC motor requiring only an ON/OFF switch and a power input jack for DC voltage (I.E: USB-C, DC Barrel Jack)

Using other types of motors like brushless motors, stepper motors, and etc will increase the complexity of the build requiring additional controllers and electronic components to your discretion as needed

Motor Specifications

Brushed DC

For espresso i recommend a rated torque of atleast 8 newton meters with a stall torque thats atleast twice that (the cheapest motor that can achieve this is a brushed dc worm gear motor / wiper motor)

For filter coffee, 4nm rated torque and atleast 8nm stall torque is recommended

Stepper Motors

With stepper motors running torque reduces when you increase it's RPM

A holding torque of 3nm with a 4x gearbox gives a usable RPM range of 0-250RPM and is able to grind for filter and espresso only with darker roasts 

Slow Feeders  and Load Reductions

The usage of a slow feeder reduces the load and allows fine grinding with light roasts even with filter specced motors 

(Editing and Assembling Electronics Housings)

For cylindrically shaped DC motors, you can use the cylindrical top housing and edit mounting holes for an ON/OFF switch and power input jack

The cylindrical top housings uses a sleeve collar on the motor that the cylindrical housing is screwed onto 

For other types of motors requiring more electronics (like brushless or stepper motors) you can edit the thick base to house the controllers, power input switches and any additional buttons, ports and cable exit routes

The thick base requires 6 sets of M5x60mm screws with its accompanying nut to attach the the bottom plate to the housing 

(Prepping your motor shaft to accept your hand grinder)

In order to do so you must slide a shaft coupler onto the motor shaft and tighten the screws followed by inserting a hex socket bit into the other end of the shaft coupler and tightening the other end

There is still some adjustability to how far the socket bit can portrude as you could slide the socket bit further down within the coupler before tightening the grub screws on it

Just in case you are using grinders with other shaft sizes, you can utilize 1/4" hex socket bit extenders (as long as it has a 1/4" hex male side) to adapt to different shaft sizes 

Mechanical Parts	Notes
Rigid Shaft Coupler (D25L40) or Jaw Shaft Coupling (D25L40)	WARNING!!!: Make sure you avoid getting the ones below that utilizes perpendicular / 90 degree orientation grub screws as it is the WRONG type (Pictured Below)  These can work for only D-Shaft motors but the socket bit must end up being glued (which is not recommended and highly prone to misalignment) Ensure one side of your coupler is sized to your motor shaft and the other side is sized to the outer diameter of your 1/4" Hex Socket Bit Adapter
1/4" Inch (6.35mm) Female Socket Bit Adapter	Most hand grinders have 1/4" inch Hex Shafts so this is recommended but you can use any other socket bit adapter to adapt any grinder that may use less standardized shaft sizes TIP: I still recommended installing 1/4" inch female hex sockets because it fits standard hex socket male to female adapter bits in order to run grinder's with different shaft sizes/shapes outside of the standard size most hand grinders utilize Be sure to measure the outer diameter to ensure you get the right sized shaft coupler TIP: Most socket bit adapters that are similar to the picture are about 11.5 to 12mm wide

(Mounting your motor)

When editing and using the sleeve style mounting blocks

This is the easiest way to mount cylindrical shaped motors but i still recommend bolting your motor down and using the blank mounting blocks for guaranteed rigidity

Measure your motors body diameter and add an extra 0.5 to 1 millimeter to the value and edit a center aligned hole with that value in the Sleeve Style Mounting Block

To assemble it requires one set of M5x30mm Screws, M5 Nuts and Two M5 Washers 

You can loosen it and slide the motor up or down to adjust its mounting height/position after the fact 

You are recommended to use a rubber band on the motor to increase friction between the motor and the mount otherwise it may only handle low torque applications like filter grinding 

When editing and using the blank mounting blocks

The blank mounting blocks provide the greatest level of holding strength for your motor rather than only relying on friction and clamping forces alone and are especially recommended for espresso based builds as the motor is fixed and bolted down with screws 

With the blank mounting blocks you will need to edit the necessary screw holes and center hole for the shaft and the block is edited where the motor is mounted high or low enough where the socket bit portrudes just enough (about 10-15mm past the bottom of the hopper)

The length between the bottom of the motor mounting block and the bottom of the hopper is 26mm as seen below as reference when you edit the mounting block

Installing the block onto the hopper

All of the motor mounting blocks require two M5 nuts on the bottom of the hopper and two M5x40mm Screws (Or M5x40mm Thumbscrews for toolless access) as pictured below

(Building the Hand Grinder Mount) 

The above image shows where the rods, bearings and leadscrews are placed

To build the Clamping Jaws you must first begin by press-fitting the 628RS bearings into the body and then the bearing cap

Afterwards you must install the leadscrew nuts into the jaws using 4 sets of M3x30mm Screws and Nuts

Thread the jaws through both sides of the leadscrew and tighten them until they touch eachother... followed by moving them into the middle of the leadscrew

Slide the leadscrew into the bearing of the body side then push the metal rods through the body and both jaws

Slide the bearing cap onto the leadscrew and metal rods and then place the M3 nut on the body then tighten the M3x30mm screw to fasten the bearing cap onto the body

Line up the jaws dead center and install the knobs (Besides my included knob design, any knob accepting an 8mm shaft diameter will do the trick like the ones pictured below)

At this point it is done and you can install it to the aluminium profile and fasten it with the M5x40mm Thumbscrews and Thumbnut (make sure you have M5 washers on both sides to even out the force)

(Assembling your Chassis and finishing the build)

The aluminium profile used is a 2020 profile with a recommended length of 25-40cm (40cm with the thick base is just nice and 25-30cm is perfect for the standard base)

If you are using the thick base, make sure you install your electronics in it and prep it before continuing to the next step

Start by installing the base onto the aluminium profile followed by the hopper, clamp jaws and accessories

All components that mount on to the Aluminium Profile requires one set of M5x40mm Screws (or Thumbscrews), M5 Nuts (or Thumbnuts) and two Washers per component

I suggest using M5x40mm Thumbscrews instead for parts where one may want to adjust its height constantly such as the Hopper, Portaholder, Clamping Jaws and ETC 

After assembling the chassis you can mount the motor that is fully assembled (shaft is prepped and installed into the mounting block) 

At this point you can wire the electronics and assemble the top housing (for a cylindrical brushed DC build) or connect the wires from the thick base onto your motor once mounted 

At this point it is complete and you can mount a grinder and run it 

(Troubleshooting Guide)

• My grinder is slipping whilst trying to grind!

  • Reason:

    • The level of friction is too low due to lack of grip

    • The level of clamping force may be too low 

  • Solutions:

    • Tighten your jaws more

    • Use the rubber bands or rubber sleeves on your grinder body (especially if the body has a smooth surface)

• My motor is slipping whilst trying to grind! (this advice only applies when using sleeve style motor mounts instead of bolting your motor down with the blank blocks)

  • Reason:

    • The level of friction is too low due to lack of grip

    • The level of clamping force may be too low 

  • Solutions:

    • Tighten your screws more

    • Print your sleeves with the correct diameter (exactly as measured on the body)

    • Use the taller sleeves for more contact area and grip levels

    • Use rubber bands on the motor body as clamping force is usually insufficient on its own and friction is required 

    • Or edit the blank mounting blocks and switch to a bolted down approach 

• My motor is stuck and it is not grinding!

  • Reason: Your motor choice is too weak for the application or the input power is too low (i.e: Light Roasts, Espresso and ETC)

  • Solutions:

    • Install a stronger motor with higher rated torque and stall torque specifications

    • Use the right power source with the correct and matching voltage, current and wattage ratings for the motor so the motor will deliver its full power 

• My parts do not fit

  • Check your slicers scaling percentage and see if your parts are dimensionally accurate, if not fix and recalibrate your print settings

• My grinder is wobbling during grinding

  • This is extremely rare and is almost impossible unless components are intentionally misaligned

  • This doesnt really affect the grinding functionality apart from spilling grounds if you do not use the grinders original catch cup but a separate catch cup placed on the base

  • This is by design and happens only when either the motor, grinder or couplers are misaligned, the motorizer design accounts for this with proper slack allocated in the tolerances to prevent any sideways stress on the grinder or motor shafts to prevent severe damage in the event of any misalignment along the drive path (especially to the hand grinder shafts)

  • Ensure you have all components aligned properly during installation 

  • Ensure printed parts are not warped