Introduction: Coffee Burr Grinder Attachment for KitchenAid Mixer

I just recently started to enjoy a cup of coffee in the morning.  I had a "helicopter blade" coffee grinder for years and decided to upgrade to a cheap hand-crank burr grinder (Kyocera CM50 - $39 on Amazon).  This grinder has conical ceramic burrs that produce a MUCH more consistent grind for drip coffee than my previous grinder.  I was astounded that I could actually taste the difference - much smoother once I found the right grind setting!

I then started looking into motorized burr grinders.  Most high quality grinders were $500+.  The cheapest conical burr grinder I could find was the Bodum which was $80.  Not bad, but I thought, why don't I make a burr grinder attachment for the KitchenAid mixer that's taking up a ton of my counterspace?

When coming up with the design, I held myself to these rules:
 1. Priced below the $80 Bodum
 2. Meet or exceed the grind quality of the Kyocera CM-50
 3. Able to be made with tools a "tinkerer" might have - no fancy CNC milling machine parts
 4. Easy setup/removal (less than 15 seconds each)

NOTE: I designed this for my Kitchen Aid 600 mixer I have a design in mind that would work for all other square-drive Kitchen Aid mixers and will post shortly.

Step 1: Parts and Tools

Essential Parts:
 1. Kyocera CM-50 ceramic burr coffee grinder ($39)
 2. Milescraft 90 degree drill adapter ($15)
 3. 3/8" x 1.25" long coupling nut ($0.99)

Parts/Materials that Can be Substituted:
 4. 3/4" x 1/8" thick aluminum bar
 5. 3/4" pine board
 6. #12 x 3" long wood screw
 7. #10 x 1" long wood screws
 8. 1/2" x 1/4" long copper tube

 - Hand drill
 - Jig saw
 - 3/8-16 die (cutting screw threads)
 - Bench grinder 

Step 2: Couple Mixer Output to 90deg Drill Input

This step converts the square drive output of the mixer to the 3/8" input shaft of the 90deg drill:

1. File/grind generous taper onto the 90deg drill input shaft.  A big taper will make it easier to cut threads in the steel

2. Use a 3/8-16 die to cut threads in the 90deg drill input shaft.  I used a wrench/vise to lock the input shaft while cutting threads.  Threading tips:
 - keep cutting die perpendicular to input shaft
 - use cutting fluid on input shaft: 3-in-1 household oil/WD-40 are OK

3. Use a bench grinder to turn one end of the 3/8-16 coupling nut into a 0.45" square.  I bought two coupling nuts: ground one into a square using digital calipers and a second using a gradual grind method (no measurements).  Calipers were much quicker, but the trial/error method worked just as well (just took 3x as long as I ground very little between trials)  Should grind at least 1/2" of the coupling nut into the 0.45 square profile.

4.  Screw the ground coupling nut to the threaded 90deg drill input shaft.  Test fit drill assembly with mixer!

Step 3: Attach 90deg Drill Output to Kyocera Grinder

1. Remove the Kyocera grinder from the shipping box.  DO NOT attach the hand-crank handle that comes with the Kyocera grinder!

2. Use drlll key to tighten drill chuck around Kyocera grinder shaft.  Make sure Kyocera grinder shaft is CENTERED in the drill chuck!  It is very easy to tighten the drill chuck uncentered.  An uncentered drill/grinder assembly will result in a wobbly/unreliable/loud grinder (but will likely work for a short time!)

Step 4: Attach Grinder to KitchenAid Mixer

Next, I had to keep the grinder assembly from falling out of the mixer. 
The mixer comes with a 5/16" screw and the drill/grinder comes with a 3/8" bolt.

I looked around my basement for anything that could connect these two.  Luckily I found some 3/4" aluminum bar that would work perfectly.  But aluminum is not necessary.  A few wraps of string, a bunch of rubber bands, etc would accomplish the same thing: Keep the grinder shaft from falling out of the mixer.

If you do want to duplicate my design, 3/4" x 1/8" aluminum bar can be found at Lowes, HD, ACE for less than $5.  i would honestly recommend looking around for an alternate before buying the aluminum as this is a low-stress part.

If you like the design/look, here's the process I used
1. Look at drill/mixer top/down
2. Sketch curve on MIN 3/4" plywood (NOTE: Gentle curves/transitions are best! Sharp bends are weak/hard-to-form)
3. Cut plywood in half with jigsaw - following sketched line
4. Place aluminum bar between plywood halves - in vise
5. Crank vise until aluminum bar is bent
6. Drill 5/16" hole in mixer end of bent bar
7. Attach bent bar to mixer
8. Mark spot where 90deg drill intersects with aluminum bar
9. Drill 3/8" hole at intersect spot
10. Connect mixer to grinder assembly

Step 5: Lockdown Grinder Rotation

The grinder attachment must be locked down in 2 rotational axis (see first pic).
The 3/4" bar can prevent rotation around the first axis, but over time could bend/break the aluminum.

1. To prevent the drill/grinder assembly from flipping around the entire mixer, I created a "boomerang" that locked into the mixer's bowl pins. See pic for boomerang dimensions.  I used 3/4" pine wood that I had laying around as this is not a high stress part.

2. To prevent the grinder from spinning around the 2nd axis it needed to be clamped down.  Here, I created a "handcuff" clamp.  See attached for clamp dimensions.

3. Drill thru hole in "handcuff" (I used 3/16" bit 2.5" deep)

4. Cut slot in "handcuff"

5. Attach "boomerang" to "handcuff"  (I used #10 x 1" long wood screws)

6. Insert #12 x 3" wood screw into "handcuff" to clamp around grinder

7. (Optioal) Sand boomerang-handcuff assembly.  Round corners with router

8. Drill 3/8" holes in "boomerang" to match Kitchen Aid mixer pins (TIP: Use Forstner drill bits in wood for crisp holes).

9. (Optional) Paint to match Kitchen Aid mixer color

Step 6: Final Assembly

Final Assembly:
 1. Tighten #12 handcuff screw to clamp Kyocera grinder.  Do not crank on screw.  Lightly tighten at first -> If grinder slips, tighten gradually until it no longer slips.  It is easy to apply enough force to the #12 screw that will crack the "handcuff" clamp.
 1. Tighten 3/8-16 "crown nut"
 2. Raise Kitchen Aid bowl holder so than pins align/insert into "boomerang"

Step 7: Using Grinder

 - For drip coffee, I tightened the adjustment nut as much as possible, then backed it off 3 notches.  BUT I highly recommend experimenting with your own settings based on your beans/brewing method.  
 - I did trial the finest grind settings in an espresso machine . . . it was too fine and only sludge came thru.  I eventually found an espresso "setting" but it took a lot of trial/error
 - Even on the Kitchen Aid #10 speed setting, there is no risk of heating/burning the beans.  IMHO, #8 was the best compromise of grind speed and loudness of machine.  Please let me know if you have any suggestions for reducing noise at top speed!

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