Home-made grinder

[matadero210]

Hi All,

I'm thinking about building a hand grinder to go with my Pavoni Mod (brew and boiler pressure gauges, PID temp control, plumbed-in). The idea is based on poking inside two Zassenhaus grinders and a few flour mills. Espressoparts.com has a bunch of replacement burrs available. My questions are:

1. what are the best burrs to get?
2. is there anything clever in the mechanical design? Or, do I just need a shaft, two sleeve or ball bearings, and maybe a thrust bearing for the adjustment plate.

I'm looking at the Mazzer Robur burrs because conical burrs are very forgiving mechanically and the pre-chop part on the burrs makes an augur unnecessary. Plus all the hype around the Robur. Anyone know if this is reasonable, or should I look at the plate burrs more closely? Anyone have a drawing of the guts of a Mazzer mill? Is there anything clever about the adjustment, or just a fine screw thread?

This is going to be a hand mill for pre-grind dose-on-demand (ie, <25g capacity) but other than that I'm open to any suggestions.

thanks in advance,
raj

[Psyd]

Anyone have a drawing of the guts of a Mazzer mill? Is there anything clever about the adjustment, or just a fine screw thread?

PM sent. Let me know when you make the second one. I got dibs!

[miKe mcKoffee]

Cool project idea. You know, one thing I've always disliked about Zass' and the like grinders is not being able to replace the burrs. And since you're doing the designing could make it so the burrs are easily replaced. Especially since using Robur burrs for low volume low speed hand grinding they will need to be replaced...someday...by your posterity in oh maybe the year 2525.
Hey, even if man isn't still alive that grinder probably will be!

[jesawdy]

It [Mazzer Robur] is forgiving, has super low RPMs (420 under load), yet it is powerful, and it can do roughly 17 grams in around 5 or 6 seconds, and the grind is superb. The conical burr set is a huge 71mm.

420 rpm / 60 seconds = 7 revs per sec * 6 seconds = 42 revolutions.... sounds doable.

Now will you need a gearbox to do it for the mechanical advantage? Probably. Now how many handcranks?

[matadero210]

Jeff,

that's a good calculation there. If the grinder is mounted to a bench, then a 1ft lever arm will probably give plenty of torque (total guess). For my flour mill, the flywheel is set up for a chain, so you can power with a stationary bike. I'm not sure I'll need to go that far for coffee: its a lot more friable than hard wheat.

I've also been wondering about roller mills, which are preferred at the industrial level (see mpechicago.com; they have a really good page of articles and whatnot: http://www.mpechicago.com/coffee/...esource-Center.htm). Have a look at the articles. I'm not above buying a few test sieves (I already have the 40 and 60 mesh) and making some crude particle-size-distribution charts. If MPE is right, and roller mills grind TOO precisely (see their comments on "plurimodal" grinding, their term for mixing streams from two different roller grinders to make a blend), this could be kinda fun.

To make a roller mill, I've contacted crankandstein.com. They are curious about how many of us there are willing to make our own hoppers, &c, to make it worth doing a batch of rollers. If they decide not, it can't be that hard to make crappy ones on a lathe. Somehow, I think the Robur handmill will do better....

I think a micrometer head or other well-marked tool for adjusting the gap would be cool, although I'm not sure how to do it yet. The Zass design just uses normal, plastic bearings and a tensioning nut on the main shaft. Anyone know how to make this more precise than the GROF FEIN marked on the Zass bench/grain grinder?

best,
raj

[matadero210]

Looking at the parts diagrams for the Mazzer Mini and Super Jolly, it seems that the beans fall into the burr set with no augur or paddles to get them going. Am I seeing this correctly? The Mazzer Mini burrs might even fit in my existing Zass housing!

raj

[matadero210]

[luca]

If you're going to make your own, you might want to get the three-phase Robur burrs. They're 83mm in diameter. A bit more difficult to find, but; hey - if you're building your own you might as well use the best! I don't know how exactly you're going to go about this, but you might want to just buy the whole burr carrier mechanism ... if it's available as spare parts.

Cheers,

Luca

[matadero210]

Luca,

I agree, but I haven't found anyplace where I can buy the 3-phase burrs. I've sent email to espressoparts.com in hopes that they can order it (they have the 110 on their website). I'm also worried that they'll cost more than the $170 of the 110v burrs. Would be a shame to pay more than Mini prices for just a set of burrs.... Anyone know where to get the 220v burrs?

raj

ps: Anyone think the LM Swift would be a better set of burrs to work from? I'm tempted because ceramic knives have been quite successful, but not sure.

[matadero210]

All,

I ordered the burrs today. In looking over the design alternatives, its not clear to me how anal the design needs to be. In Zassenhaus mills, the shaft typically has only one bearing, so that the inner conical element has a degree of wobble. This seems unlikely to be a good idea, although Zass has a good reputation for espresso grinding. Assuming I use two bearings, the only question left is how to do the adjustments.

I'd like to use a micrometer screw in the bottom of the mill to do the adjusting. In this case, the outer burr would be fixed, while the inner burr would move up and down, along the shaft, held by the screw on one side and a spring on the other. With 10# of pre-load, maybe the wobble caused by hand grinding will not affect the burr, but that's my main concern. (basically, I don't want the grind to change as I change my handle grip).

Lastly, I'm not sure how to insure that both burrs are centered perfectly (other than being careful while milling and drilling).

Will try to post some design ideas soon,

raj

[jesawdy]

I ordered the burrs today.

You're a mad man! I am very curious to see what you come up with and most importantly if it will work. (Should I order my burr set now? )

[matadero210]

Hey, Jeff, I'll take that as a compliment.

I took apart my two Zass mills over the weekend, one Turkish and one Grain (the one with the wooden body). The Turkish mill had been giving me some trouble--not able to grind fine enough to play with light tamps (at #30 tamp, it was fine). Wow--the burrs were a mess! Some of the teeth were basically chipped, but in a way that really looks like they fractured off or were never there to start. Maybe I shouldn't have bought it on ebay, but there was no place else (Yay that the factory is back in operation!).

Anyway, I spent two hours with a dremel tool and carbide bit and now it looks much better. Both Zass mills are single bearing, so I'm wondering if that's the way to go.

The burrs won't be here for two weeks, but in the meantime I need to find a cheap source of SS for the body of the mill. I'm glad I only need 3" material and didn't try to get the 220v burrs--they would be too large

A quick sketch of my current plan (I failed kindergarten, so sue me)



Its very simple: a top piece to mount the top bearing, a bottom piece to mount the bottom bearing. Both of them precisely positioned with shoulders onto the outer burr and screwed together (not shown). The spring presses the inner burr against a shoulder in the shaft (the inner burr is keyed, not shown), which is pushed against a ball bearing and a micrometer screw. The screw is marked with 10um increments. Espresso is ground at 600-200um, so I should have plenty of resolution. The base may be thicker or thinner, depending on how the micrometer mounts on. Only 20g of beans may be inserted into the top cavity through a hole in the top, not shown. The bottom will have some sort of window or chute to recover the 20g of grinds (once I measure the volume of 20g of grinds). The only hard part I foresee is the extensive boring to make the upper and lower cavities. Lots of cutting, and very expensive starting material. Obviously the screw sticking out the bottom is less than idea, but I haven't thought of a better way, yet.

[espressme]

Its very simple: a top piece to mount the top bearing, a bottom piece to mount the bottom bearing. Both of them precisely positioned with shoulders onto the outer burr and screwed together (not shown). The spring presses the inner burr against a shoulder in the shaft (the inner burr is keyed, not shown), which is pushed against a ball bearing and a micrometer screw. The screw is marked with 10um increments. Espresso is ground at 600-200um, so I should have plenty of resolution. The base may be thicker or thinner, depending on how the micrometer mounts on. Only 20g of beans may be inserted into the top cavity through a hole in the top, not shown. The bottom will have some sort of window or chute to recover the 20g of grinds (once I measure the volume of 20g of grinds). The only hard part I foresee is the extensive boring to make the upper and lower cavities. Lots of cutting, and very expensive starting material. Obviously the screw sticking out the bottom is less than idea, but I haven't thought of a better way, yet.

I have found that, If I approach a local machine shop with a pound of pour-over grind for their Mr Coffee, they are almost eager to let me get at their drops ( short pieces.) Scrap is much cheaper than new ( about a buck a pound rather than $7.50. )
Another place ( cheapest I've found) is : Check Here
Good Luck!
rp

[jesawdy]

Do you think you could prototype the body of the thing with hardwood? This will give you a cheaper/faster way to work out the nitty gritty of the design and to see if it has some serious shortfalls.

It would be really cool if you could get the thing to work without the lower bearing, perhaps with a longer upper shaft with two bearings above and all the adjustment business up top. This sort of design would allow the grind to drop into a drawer, compartment, funnel, waiting basket etc, but it presents other problems as well.

[matadero210]

Jeff and Richard,

Thanks for the pointers/suggestions. After spending some time on mcmaster, the new materials cost is now about $60. We'll see what scrap I can find when my wife lets me borrow her car (I'm on a bike).

I agree the bottom half design needs more good ideas. In the best of all worlds, I'd like to grind into the basket by inserting the basket into the mill before the coffee. Then, when its done, shaking the entire thing to de-clump/distribute before removing the basket.

The bottom bearing is not what keeps the beast from standing straight: its the micrometer screw. It took me a while to figure out that the micrometer screw is 25mil/turn = 40 threads/inch. So it doesn't really represent any greater adjustability, just a nice scale. So a 2-56 screw with a nice, large wheel would be a better adjustor and take almost no space. With that change, it might be possible to mount the basket underneath the adjusting screw .....

More to think about.

raj

PS: PORTAFILTER BASKETS ARE MAGNETIC STEEL! So the base of the mill should have a small bearing, a 2-56 adjusting screw, a slot or two for grounds to pass, and a magnet. The basket can stick to the bottom of the mill, and one can mill directly into it, shake and settle, then detach and tamp.

PPS: Baskets are made from stainless that work hardens, I think, because the magnetic susceptibility seems quite variable. I tested 4 baskets, and they were all over the place in terms of sticking force to a refrigerator magnet. So, I'm not sure magnetic attachment of the basket is a good idea. Still not sure how to handle the grinds.

[matadero210]

A brief update for those following the thread:

1. burrs should be here in a day or two. took longer than I thought for Owen to get them.

2. I have debated the one v. two bearing question with several very smart people. One bearing: this seems to be how Mazzer does it, with precise control along the axle (which controls particle size), but play in the other two directions; the mill self-centers on its own. Two bearings: no one does this, and there is a fear that if its not done right, it will be much less precise than self-centering. So I'm going to start with a single bearing. The two bearing option, partly sketched above, can be retrofitted.

3. adjustability is important. if optimum grind size is 300um for espresso, then most current designs which depend on 20-30 threads/inch are 1/4 turn from dead zero (300um = 0.012"=1/80"). at 100tpi, about the best tap and die can do easily, espresso is 1.2 turns from dead zero. my plan is to use 127tpi screw/bushing pair manufactured for optics with a 4:1 lever action that will make my mill operate 6 turns from dead zero/500tpi.

Will post sketch soon. I would like to make this wall mounted rather than knee/hand mounted, but haven't figured out the 90 degree rotation yet. I think the first version will be pepper-grinder style.

Anyone have a ro-tap system to measure quality of grind?

raj

[Jacob]

... One bearing: this seems to be how Mazzer does it, with precise control along the axle (which controls particle size), but play in the other two directions; the mill self-centers on its own...

On the Robur: The short axle that holds the inner-burr is supported by two bearings "B" and "C".
This short axle are meeting up with the axle from the motor inside "A" where bearing "B" is located.

[matadero210]

Hi Jacob,

In the drawing, however, its not clear that the outer burr is held firm. The three springs are used to press the outer burr housing (18) against the adjustment collar, but what keeps it from moving laterally? From what I can tell, the outer burr and housing are free to move in 2 dimensions by at least a few mils. Given that espresso grinds are 12 mils, that's a huge amount of play. Can anyone who has a Robur confirm that the outer burrs have a bit of lateral play? In my design I'm reversing the play: letting the inner burr move laterally while keeping the outer burr in place.

raj

[Jacob]

... but what keeps it from moving laterally?

Inside diameter of the 'main-' housing - And I don't think there is more free play than what is needed for the hot grinder to be adjusted.

AFAIK you want the burrs as fixed as solid as possible!

[Everman]

I think the most important thing is to make sure the burr carrier is solid enough to not let the burrs wobble "at all" in any direction. Unless you have access to some precision machine shop equipment, or use an already made burr carrier off a robur (or whatever else that's high end), it's going to be difficult.

I look forward to seeing your progress, should be interesting.