Homemade Coffee Burr Grinder

This project was inspired by jeffkobi's Coffee Burr Grinder Attachment for KitchenAid Mixer.  I was perusing past contests and discovered his winning entry in the coffee contest.  I loved it.  

The power take off on the Kitchenaid mixer is definitely an underutilized resource and his use of it was inspired.  I decided to make my own version of the same concept...well...because I wanted to.

 Let's proceed shall we?

I used the head of an angle grinder to transfer power from the mixer to the coffee grinder.  My coffee grinder was hiding as a peppermill right under my nose!  Some copper sheet did the job of connecting the grinder head to the coffee mill.

The grinder head is perfect for transferring power from the mixer but it needs some modification to adapt it.

Kitchenaid attachments all have a square drive shaft that rotates inside of a cylindrical sleeve. The drive shaft fits into a square socket in the mixer and a set screw holds everything together.  I didn't want to feel left out so I decided to emulate this arrangement.

I had a threaded drill attachment that I ground square on one end to fit into the mixer.  The other end had a male thread so I drilled and tapped a hole into the shaft of the grinder to accommodate it.  I don't have a metal lathe but my friend has a wood lathe that worked just fine for this. 

Once I had a drive shaft it was time to work on the outer sleeve.  I did some testing and discovered that 1/2" black pipe made a decent substitute for the sleeve.  It fit into the mixer with only a little bit of play.  Nothing the set screw couldn't handle.  Not bad for an off the shelf solution.  

The next task was figuring out fow to attach the pipe to the grinder.  Lacking a real metal lathe I looked at plumbing parts for a solution.  I ended up going with a floor flange.  It was enormous compared to the face of the grinder but I figured that could be remedied.  

I started by cutting the flange down with a metal cutting chop saw until I had a square about the size I needed.  I mounted this in the lathe and took an angle grinder to it until I had an approximation of a circular flange that matched the grinder.  It still had that handmade look but that's OK.  

The last part of this was to mount the flange to the grinder.  I drilled and tapped some holes for some small socket head screws.  The tolerances were rather close so it was quite a bit of fiddly work but in the end it got worked out.  

The other end of the grinder head was a breeze.  The coffee mill also had a square shaft.  It was dimensioned perfectly for the square end of a 3/8" socket. The shaft coming out of the grinder head had a layer of fiberglass over it and fit very snugly into an 11mm socket so I just took the socket and hammered it onto the shaft.  It friction fit perfectly!

I took the pepper/coffee mill apart just to be sure it was indeed a burr grinder and would work.  It looked like it had the right stuff to me.  I ran a test batch of coffee through it and it worked well albeit slowly.  All the more reason to motorize it!

 

I didn't want to demolish the grinder in the process of doing this project so I thought a long time about how to bring the coffee mill and the angle grinder together.

I ended up prototyping in cardboard until I had a design that I was happy with.  It only required one set screw into the coffee mill and attached to existing holes in the grinder head.

I transferred my cardboard patterns to copper sheet and cut it out with shears.  I decided to rivet it together because it just seemed like the right thing to do.  I punched holes in the copper sheet and used some copper roofing nails as rivets.  A piece of patio furniture leg made a good impromptu anvil.  

After the cylinder for the attachment was fabricated I cut out the spout for the top and attached it with rivets as well.