I'm going to use this thread to document making a grinder using Robur burrs. If this actually works, I'll go back through the thread and clean it up a bit.

What I ordered:



What I got:



July 12, 2011

Bronze bearing before cutting in half and machining the inside for a tight fit to the lower burr. I was going for an interference fit, but... that's what Loctite is for.



Lower burr fit to bronze bearing:



Tomorrow: Threading the outside of the bronze bearing

July 13, 2011
Trued the bronze bearing to the lower burr holder outer circumference. I don't know if this will be precise enough-- I don't know if the burrs are cut truly concentric to the circumference or whether the mounting holes are the reference point. I also don't know what sort of tolerances I should be working at.

Bronze bearing true to burr:



Then threaded the bearing. At first I thought of doing 56 TPI, but then decided to do 22 TPI which won't allow as much leeway in dialing in the grinder, but seemed close to 1mm threads that someone mentioned the Mazzer Mini uses.



Here's a video of cutting threads on a very old lathe using lard:

http://www.youtube.com/watch?v=f5CBtp4VuqU

Next step is to layout the shaft which will be 3/4" stainless turned down to 5/8" for part of it to slip into the bearings. The bottom will be slotted to hold the lower burr and also threaded to keep the burr from dropping off. Inside thread as well to be used for centering the inside burr to the outside burr. Top will be slotted and threaded to hold a hand crank for use in off the grid mode.

As a Pharos owner, I'm very interested to see how this turns out.

Sweet...... Ive got a lathe and a milling machine, If you need anything done let me know.....

Looking forward to the finished setup

Thanks, Adam. I think I have what I need, though I have to do my milling on my lathe... isn't great, I know. So here is what I just ordered. It will be used to hold the pillow blocks (which hold the shaft) and the 3/4" aluminum plate that will be threaded to hold the lower burr. That should lock everything that matters into a nice 90 degree position. The angle plate then can be attached to whatever...



I think the key to this is going to be good alignment of the lower burr to the shaft. To do that I'll make a jig that is made at the same time I spin the hole in the aluminum plate. It should allow for perfect concentricity (perfect, I know, isn't possible).

Including the burrs, I think I just hit about $200 in materials and I'm hoping it won't exceed $245 (For the crank operated part. I have a motor already.) It makes me appreciate that as expensive as the Versalab is, in terms of labor and parts, not to mention design, it really is quite reasonable. However, I'm hoping to have a dual powered grinder -- hand for times when it is already dialed in and motor for times when I have "customers".

I originally thought I'd use 5/8 " shaft, but now I'm reconsidering and thinking 3/4" might be better. These are not high precision bearings, and I'm not sure if they will be good enough. If it turns out that I need more precision, I'll do a Version II with better bearings.



A couple rough layouts. I'd rather have the pulley between the bearings but that will make the grinder higher. My hope is 3/4" shaft will provide the stiffness.

Strangely, the burrs shown on the EP website aren't the same as the ones they sent you. 12 vs 10 pointed star.

How are you going to lock grind settings?
Do you have any idea on what motor you will use?

I am very interested in how this turns out. Best of luck.

Here are my thoughts, Roeland:

1. I'm making a prototype, so most of what I'm doing is reversible (the bronze ring isn't going to be easy to reverse, though).

2. I happen to have a 1/2 HP DC motor with speed control that I will use, at least to try.

3. The thing that worries me is my machining ability, or lack thereof, as related to the precision needed. I have a theory that could be entirely wrong, that precision is not as high as might be thought. For example, the Versalab with its overhanging, one bearing design, MUST have flex as it operates. There are no two ways about it. I suspect the beans themselves may have a centering influence.

The Pharos has two bearings capturing the burr. That's a good thing for precision, but causes other user inconveniences. In addition, I don't think the Pharos is immune from flex (it's shaft looks pretty thin) and the bearing themselves are not high precision bearings. The adjustment is moving the shaft up or down through bronze bearings, and that itself is inherently not precise due to the play needed between the bearing and the shaft, which will increase over time. However, it would be easy and cheap to replace the bearings if necessary after some years. I wish the aluminum disks that hold the bearings were at least 1/4" thick, which would be good all around. The locking mechanism also looks like it might reduce precision. [I am not knocking the Pharos or OE or anyone who bought one or wants to buy one. If Doug says they are great they are great.] I'm just making some observations.

Both the Pharos and Versalab produce acceptable fluffy grinds for espresso.

On the other hand, the Spong No. 3, which I reviewed, is incredibly imprecise and it can make fluffy grinds suitable for espresso.

4. Locking the burr in place is an easy matter-- I haven't decided exactly how, but there is nothing to it. I modified a Rossi 45 with such a locking mechanism, as documented elsewhere. Speaking of which, it also was not a precise machine-- you could feel play in the burr assembly-- slight, but it was there. My lock removed the play, and probably pushed the burrs very slightly off center.

So, we'll see. There are a couple more things to do before I can try it out-- machine the shaft and the lower burr holder-- and assemble them. I'm going to make the whole thing easy to take apart. If it looks like it might give good results after some months of use, I'll think about having a water jet service cut some pieces of aluminum plate and make a more acceptable aesthetic version. Or more likely, I will intend to and will instead make a spring lever machine of my own design.

What I'm trying to make here is a hybrid design, a motorized, one dose grinder that can also be hand cranked.

Spitz.me wrote:As a Pharos owner, I'm very interested to see how this turns out.

DJR,
There's more than one person anxiously watching your progress.
-Ed

Small progress:

Got the angle plate from Grizzly and rough cut some aluminum plate to hold the lower burr and the pillow bearings/inner burr.



After reading comments from OE re: burr alignment, I checked the Robur burr fit. They don't wobble, but the inner burr is .007" higher (protrudes from the bottom) of the outer burr. At that setting there would be no way for coffee to make its way out. But it doesn't wobble at all.



When I assemble the grinder I will have the lower and the inner burr locked together firmly and then carefully bolt the assembly together. I'm hoping this will guarantee sufficient alignment. I'll place three pieces of paper between the burrs so I can really clamp them tight. The jig for doing this will be made at the same time as the outer burr outer holder, so everything will be concentric. At least that's my hope. I still wish I knew what, if anything the use of springs does, but it isn't obvious to me.

Suggestions, always more than welcome.

Cool project, very curious to see how it turns out...

Something I can think of is that the springs in Mazzer design might be better locking mechanism since it pushes the burrs [more] evenly.... as opposed to a locking screw, such as in K10, that probably causes them to be slightly misaligned.