Bump for subscription to this mad project! I love it.

I don't mean to be arguementative, but I'm not sure I agree with Jacob and Everman. I guess a measurement of the lateral play of the outer burr in a real machine would shut me up, but I think Zassenhaus designs -- all conical burr -- are free to wiggle laterally. That's because when grist is present it only takes a half turn of the axle to self-center the inner burr. So, the only precision bearing is in the axle direction.

Regardless, I'm planning to machine a brass housing along the lines of a zassenhaus design and see how it works (I have access to a mill and lathe). The design will leave open the possibility of a second bearing to lock everything down, as suggested. One question I haven't resolved: how do we judge grinder quality? The only reproducible way is to use a series of test sieves, but that's going to cost $150-ish. So, I'll start with microscope pictures of the grist and see how that looks. But it sure would be great to set up test sieves and get samples from everybody: we could assemble a database of grind distributions! Maybe my wife will buy me test sieves for my birthday.

r

Hi all,

I disappeared the last month to finish my home-made lever machine Robo-Pavoni; learning to make espresso machine from scratch. Now that it's finished, I'm ready to take another look at the grinder project. Thus far, I have some rough drawings. Please forgive the roughness, I'm just learning SolidWorks, but I wanted to share what I have thus far.







The basic innovation is to use a lever with the adjuster. The adjuster itself is 100tpi screw, which is 3 or more times finer than any existing mill, I think. With the lever on the top, the force on the screw is reduced by 3x, while the tpi is effectively 300. This means that 1 turn of the screw should give .003" displacement, about a fourth of the optimum espresso particle diameter. Thus, my grinder will be 4 full rotations of the screw from choking. The screw, of which only the bushing is shown, will have an allen key to give a 4" radius. The fulcrum is the thinned material to the left of the shaft.

The shaft needs further refinement (the Robur burrs are 14mm ID, not quite .500", and the various clip rings and bosses need to be added), and the bottom bearing needs a rework. I'm not sure about the bench: my tests at home suggest that the mill should fit into a housing (fine hardwood?) that clamps to the bench or my espresso machine so that it only takes 1 hand to crank and none to hold the mill. The burr as shown (in the middle of it all) is assumed to have flat faces that top and bottom brackets can reference.

raj

Hi All,

We'll, I finished my Rajjenhaus Robur! Based on consultation with many mechanical engineers, I decided to omit the bottom bearing for the time being (Versalab's omission of a bottom bearing was decisive). The other change relative to the drawings above was to make the flexure out of a second piece of brass, pinned to the body. This was primarily for ease of manufacture. I'm hoping to do a video, but here are stills (the color is off: the body is brass and the burr, at bottom, is steel):



You'll notice that I've used the crank from my Zassenhaus Turkish mill. There are some stainless shims to establish the basic grind, and the 100tpi screw for day-to-day adjustments. My first shots give 1 complete rotation of the screw = 10-15 sec of shot time. The knob is nice for general adjustments, but there's a socket for an allen key which allows maybe 30-50 positions per rotation. Now that's adjustability.

I machined a 1.5 kg stainless tamper a while ago I wanted to see if I could use only the weight of the tamper, with NO additional force. That proved impossible before, but is easy as pie with the new grinder. Now I just rest the tamper in the basket, give a 90 degree turn, and repeat once. Seems to be quite reproducible. You'll notice the robo-pavoni in the background. It now sports an insulated boiler and is controlled to 0.1C. For more on that, see Robo-Pavoni; learning to make espresso machine from scratch



I'll work on money shots, but double ristretto gives 8-10mm crema and an improved flavor over my previous grinder (Zass grain mill). Normal doubles give 6-8mm crema. Flavor is definitely richer than before, more transparent.

I'm thinking about a base so that I don't have to hold the grinder while cranking and a receiver that would allow grind-into-basket with a guide to ensure normality of tamping (ie, the mill would lift out of the base/receiver and the tamp would be dropped in. The funnel would guide the tamper to be vertical). But so far its fine as-is. A grind takes about 100 turns (80-120 is the range thus far).

raj

ps: I got a set of super-jolly burrs a few weeks ago. It would be nice to make a grinder for those too, but I've used up my free time for a while.

You sir, are a wild man- I love your ability to make proto-types-you have to hold it to know what you like and don't like. I did this also when developing my stove and stand designs for Mo-Go-Gear... not to mention the tooling and jigs for production. There just weren't any stores to go buy off the shelf stuff.... Thanks for living outside the box ..

Hi Raj,
That do mean king! Thanks for stretching the limits! on the cheap!
richard

It looks like you have a nice adjuster solution, but perhaps limited in range. I just read this thread today, so this suggestion is a little late, but maybe for the next one?

Some planes (for planing wood) use a differential screw-thread for fine adjustment. Basically, you have a fixed inner screw with an internally threaded shaft from the adjusting knob running on it. This shaft also has external threads of a slightly different pitch which mate with internal threads on the thing-to-be-adjusted.

So the movement is the difference between the thread pitchess. For example, with 3 tpi and 4 tpi you would get 1/3 minus 1/4 or 4/12-3/12=1/12 inch/turn. Clearly, you can get movement about as fine as you could want. Without flimsey super-fine threads.

Hope that's understandable.

Hi Dick,

A good idea. I have a differential screw with 0.5um markings--I thought that might be a bit too extreme for this! It's sitting in my bag of tricks for some other project ....

raj

ps: you are right about the limited range: its about 6 turns = 20mils vertically, enough for espresso, but not the full range of coffee grinds. One mill per brewing method .... (insert LOTR humor here)

Hi Dick,

I was thinking about your differential screw idea. To me, a differential screw is a $400 item that you buy (as it is in optics, in which I was trained). But reading through the lit, your idea is a great one. If I threaded my axle with M4 x 0.7 and had a keyed bushing with M5x0.8, then a simple coupling with M4 and M5 at either end would give 100um per turn (or 1/4-27 and 1/4-28, which gives 1/27"-1/28" ~ 35um/turn). My present design has 250um/turn on the end of the lever (and <100um / turn actual adjustment)--with your design I could achieve the same performance without the lever and with greater total adjustability.

I may have to buy more axle material and try a retrofit. Its a good thing I pinned the lever--it comes right off. Now that you mention it, why doesn't Mazzer do this themselves? It would be pretty easy given how their adjustment mechanism works. Patent it and then sell them the idea!

raj

matadero210 wrote:I'm hoping to do a video, but here are stills <snip>

I'd love to see how you use and adjust it. (video posting help)