Let's Build a Flat Burr Coffee Grinder

[Stavros]

Hi Guys,

Firstly - the design. Basically, I started with a set of Mazzer Major 83mm flat burrs burrs, two SKF 80mm x 50mm x 16mm deep-groove ball bearings, a 375 watt three-phase electric motor with a 9:1 planetary gearbox, a single-to-three phase variable frequency drive, and 12kg of 150mm and 100mm 6061 aluminum bar.





I spent quite a few night on the CAD package designing the grinder. Wherever possible, I applied good engineering practices, (typically used for machine spindles and shafts on lathes, pumps,etc), to maintain axial alignment and parallel faces. Initially Iwas planning to mount the rotating burr carrier directly onto the output shaftof the gearbox, as it is fairly rigid, and is supported in a reasonable sized bearing. This would have greatly simplified the design, and made it quite compact.



However, call me stupid, but I decided touse a completely separate one-piece shaft and carrier, supported between two ball bearings, and connect it to the gearbox with a flexible coupling. This allowed me to use an adjustable nut to preload the bearings to remove any axial and radial play. It would also allow me to fit a different motor/gearbox one day if required.





Now just to clarify, I’m not trying to built a commercial grade grinder, or a mega-grinder. It only has a 375 watt motor, with a 9:1 ratio gearbox, so it will grind at a moderate 300 rpm. With frequency control, I can ramp the speed up to a max of 600 rpm. That's pretty much in the ballpark with other domestic grinders. I’m just trying to keep the burrs consistently aligned and spaced apart.

Cheers, Steve

[Stavros]

Hi Guy

Twelve or so years ago, my first ‘coffee machine’ was a Braun Espresso Master, which came with a Braun spice grinder. Wow, I was set, and had ‘real’ coffee. The nasty little Braun is long gone, but the grinder lives on as a great spice grinder.

When the Braun died, I started reading up and visiting forums, over-researching things in my usual aspergers-like fashion. Based on reviews and opinions on this forum, I got a second-hand Rancilio Audrey, which came with a Sunbeam EM0480 grinder. Now I was cooking with gas. While Audrey was a weapon compared to the Braun, the EM0480 was a nightmare – plastic gears, wobbly burrs, wear and tear, needing shims to keep it grinding fine, it wore out in no time – you know the story.

So, back to the forum, and I picked up a second-hand Rocky grinder of Fleabay, and fitted new burrs. After the EM0480, the Rocky impressed me – steel, brass, aluminum, smooth, and heft, mucho heft. (The mother-in-law will attest to this, she picked it up from Taree, and brought him down to Canberra in her carry-on luggage.) And better yet, Rocky, like Audrey, was pull-apart-able. No silly plastic clips, but real threads and fasteners. They were designed to be repaired - to live forever. Now Rocky isn’t perfect, the adjusting thread is a bit loose, the speed is a bit fast, and the adjusting detent is a little coarse. As per advice on the forum, Teflon tape fixed two of the problems, and Rocky is well loved.

Now, I’m not fanatical about my coffee, but I am a bit of a tinkerer. And as a retired machinist with too much time on his hands, and a workshop full of machinery, I sometimes start projects for projects sake. So it wasn’t surprising that I kept thinking someone could build a better grinder. All you need to do was attach a couple of big flat burrs to a variable speed geared motor. How hard could it be? More like how crazy would you be to do it!



This thread will cover the build of the grinder. More to come, , , ,

Cheers, Steve.