Gaggia MDF not grinding fine enough, uneven burr spin

[dsc]

Hello,

I already talked about this problem on the TMC forum, but I thought that maybe someone here will have some new ideas regarding my problem.

Recently I dismantled my Gaggia MDF grinder to clean it and because I wanted to check if there's nothing wrong with it as it emitted a weird sound like something was rubbing against something inside. So I took everything to pieces, removed the burrs, cleaned them, cleaned the whole burrs chamber and put it back together:





The bottom burr was removed from the metal piece that was holding it. Everything looks like this:



Now after putting it back I tested the grinder without the upper burr in place and sadly discovered that the bottom burr spins unevenly:

http://s14.photobucket.com/albums...ew&current=mdf.flv

[WARNING: the video is quite loud so turn down your speakers]

Tried to center the bottom burr but I was unsuccessful, so decided to leave it as it is. I added the teflon tape mod to make the grinder stepless and it all looked good until I used it. I remember using a setting of around 2 to achieve a pretty slow pour, so I set it to that. Got a really fast pour. Turned it down to 1.5 and it looked pretty good, but I'm working really close to the 1 setting which is when the burrs almost touch (I got the burrs to touch and backed out until there was no metal vs. metal sound present, that was my new 1 setting). I was a bit surprised to see this, but blamed it on the coffee (best before 07-2008 and packed, not fresh roasted). Today I got a pack of coffee which was roasted 6 days ago, so not amazing, but still pretty fresh. I backed out to the setting of 2 because I though fresh coffee means having to grind a bit coarser. Well it turns out I was wrong, I got a real gusher and had almost 100ml of espresso 15s later. I got back to the 1.5 setting but haven't tested that yet.

So I don't know what to do. Before dismantling the whole thing I used to grind on the setting of 2-2.5 (which is still pretty low), now it's more like 1-1.5 where 1 means the burrs are only mm away from each other. I think that the uncentered spin has smth to do with. Have someone ever had similar problems?

If you have any ideas feel free to post:) I'm all ears:)

Cheers,
dsc.

[dsc]

Hello again,

so today I used that 6 days old coffee (well it's 7 days old now) and made a shot on the setting of 1 on my MDF. Here's how it looked:



[WARNING: the video is pretty loud, so be sure to turn down the volume]

Massive blond gusher around the 12s. What the hell?

My dose is 18.5g, I get a nice solid puck, no holes, shower screen impression. I use an electronic scale to weigh the grind, grind into a small cup and than dose form the cup to the basket in my NPF. I'm also using WDT and a 4 sided tamp (around 20kg) to secure the sides of the basket as my tamper is a tad smaller than it should be.

I will dismantle the MDF again today, but why am I getting such fast blonding? Is it all because of my technique or can smth else be blamed?

Cheers,
dsc.

[jesawdy]

My thoughts on the grinder runout would be to try turning the lower burr set 120 degrees in either direction and see if it improves. I would be less concerned about runout in the horizontal plane compared to the vertical plane (what I would call a wobble). Provided the clearance at the flats of the burrs are the same around the perimeter, it would likely not matter as much.

That said, you feel you are experiencing problems. Before you get too worried, I'd try another batch of coffee.

Massive blond gusher around the 12s. What the hell?

My dose is 18.5g, I get a nice solid puck, no holes, shower screen impression. I use an electronic scale to weigh the grind, grind into a small cup and than dose form the cup to the basket in my NPF. I'm also using WDT and a 4 sided tamp (around 20kg) to secure the sides of the basket as my tamper is a tad smaller than it should be.

Well, you got a big cone there, and a few spritzies, but what was your final volume (with some crema rest time) and how did it taste? I will see similar large cones on Silvia with fresh coffee, certain coffees and updosed baskets that the end up contacting the showerscreen with swelling. Most of the time, less coffee and a finer grind and the cone stays reasonable. Of course you're not sure you can grind any finer and that might be a problem...

[Spresso_Bean]

The burrs should almost center themselves but there could be a slight manufacturing or quality control issue with yours - not sure how thoroughly Gaggia checks them out but I'd guess it's pretty good. Haven't seen too many issues with the MDFs. One thing to try if you hadn't already, is to remove the screws holding the burr and then go back and screw each of them in loosely. If you tighten one all the way and then go to the next and then the third you might end up with a centering issue, but if you do a little at a time going from one to the next (clockwise for example) then it should center itself pretty well. Hopefully that makes sense.

[HB]

Massive blond gusher around the 12s. What the hell?

At first glance, it looks like very fresh coffee, but you say it's been around for a week. Does the blend include Robusta (Monsooned Malabar)? It's known the "cone explosion" depicted in your video.

[dsc]

Hi everyone,

jesawdy: I already tried turning the burrs in different directions. The thing is that they have some space around the screws that hold them, so you can manouver them a bit. It's hard to set them directly centered but I will try my best. I also want to change the teflon tape mod to the worm gear mod described here:

http://www.home-barista.com/forum...er-t664.html#18378

I tried using less coffee (doses of around 14-15g) but always got channeling and a lot of spritzies. Overdosing tends to get rid of that, although I need to grind fine enough to control the time, which I can't do really because I'm already at the lowest setting.

Spresso_Bean: yeah that what I was doing, although it's pretty hard to get them centered. I will try it out again while changing the stepless mod.

HB: nope it's pure arabica, Bali "God mountain" to be precise. Roasted on 10-04-2007. What made you say that it looks very fresh?

Yesterday I tried split dosing and double tamping. Spilled around 9g of coffee into the basket, distributed using this:



tapped on the counter lightly to settle the grounds and tamped with around 15kg. Put the rest of the dose into the basket, distrubuted and tamped with around 20kg. The effect was a very slow, almost choking, pour which took around 40s to give 60ml. You could even see how the middle of the basket stays blank for around 15s, because my convex tamper compresses the coffee in the middle more than on the sides. Tried the same technique today, but changed the grinder setting to 1.5 and I got a blond gusher + express pour, which is a bit wierd.

Oh forgot to add the pressure on my Classic is somewhere around 8.5bar, changed my OPV setting a while ago using the glass and characteristic method described on the forums.

Should I blame my technique?

Cheers,
dsc.

[dsc]

Hi again,

today I got the bottom burr centered and it spins evenly (at least it looks so). This didn't change anything and I get coarse grinds even when the burrs are less than 0,5mm away from each other (almost touching I would say 0,2mm max). I guess I have to buy new burrs...

One question: when you grind really fine do you get coffee powder? something like powdered sugar? because I get something like a mix of really really fine sand and powder. Sadly there's more "sand like" particles than powder (I can feel it when I rub it with my fingers). Could unparallel burrs cause something like this?

Cheers,
dsc.

EDIT:
here's how the bottom burr looks like, there's a small damage that has been highlighted:

[HB]

One question: when you grind really fine do you get coffee powder? something like powdered sugar?

All grinders produce some fines; the better ones produce a consistent distribution of fines and coarser grinds. The textures isn't like powdered sugar, which is extremely uniform. It's more like white pepper.

here's how the bottom burr looks like, there's a small damage that has been highlighted:

Sorry, looks like game over to me.

[dsc]

Hi,

I checked the grind and rubbed it against my fingers. There are a lot of fine particles that don't break up, I mean it's like very fine sand, only smaller than sand. The rest is powderylike.

Today I put back the two pushers that a part of the stepped mechanism. They seem to be doing a good job in eliminating the upper burr carrier thread play. Without them it just moves a lot and that's why I got sucha coarse grind on such a low setting, the burrs were close together, but when they started grinding, the upper piece moved a lot creating an uneven and coarse grind. So I'm back with a stepped grinder, but got this today:



so I guess it's not all bad. Something finally works, so one thumb up.

The next thing is to remove the stepped regulation, but leave the pusher. I will have to add some kind of plate to cover the carriers depressions on it's underside. I will also have to add something to hold the upper burr while the grinder works, but that's a totally different story. Oh and have to get the burrs parallel, because the lower burr is slightly off.

I guess that small damage in the bottom burr isn't that bad. I know it affects the grind, but maybe not as much as I thought it would.

Cheers,
dsc.