Home-made grinder - Page 3

[terryz]

I tried the electric pepper mill Michael.

Should I have replaced the pepper with coffee, cause this tastes like liquid pepper

[mathias]

I bought the 71mm, because they were cheap(er) and available. The bigger diameter works against a hand grinder, which is already free of over-heating problems. Increased diameter would increase the torque needed--and its a fairly firm crank at 71. It would be a lot easier if my hand was larger or the mill smaller (71 for the burrs, 74mm is my OD for the mill).

Thanks!

How much force do you think you use and how long is the Zass crank you use?

[Sleepless]

In other news: I'm thinking about a grinder that uses differential screws. This would be two plates, with flat burrs mounted on each, and an axle and crank.

Raj,

Don't you think that conical burrs more completely expel all the ground coffee better than the flat burrs would? You could probably rig some sort of cam lock to open up the gap between the conical burrs to thoroughly clean them, as well.

- Steve

[matadero210]

Mathias - its about 4"--from the Zass Turkish mill. I'm not good a guessing force, but I'm a dedicated couch potato/nerd, so it can't be that hard.

Steve - Maybe some kind of augur would help keep the space in the mill clear, but you are probably right about conicals generally expelling better. They have gravity working for them. I'll try to post a drawing of my current design ideas--there is screw that allows dissassembly and cleaning without messing with the grind settings (as there is on my conical design).

raj

[knewmans]

Perhaps a crank like this one on ebay - 190131506249 - would make it easier.

[arriflex]

That's fantastic! Another place for handles might be at Grizzly.com


I'd love to take a shot at a project like this. I've got a machine shop that I am learning how to use and this and the marriage threads are looking very intriguing as useful projects. I'd love to see a disassembly of your grinder too someday.

arri

[arriflex]

Okeedokee, I've acquired a set of 71mm robur conical burrs. Well, actually, they're on their way. I am dreaming up designs to play with and really appreciate what has been done here. I agree that differential screw maybe a fantastic way to adjust. The versalab is a nice starting point... build a simple container to hold the fixed burr, and suspend the cone from the top with two bearings. I imagine there should be a thrust bearing of some sort to take the grinding force trying to separate the burrs?

In hindsight, did you end up being content without having bearings or support on both sides of the burr? I realize versalab does it without as well.

arri

[matadero210]

Hi Arri,

Yes, I think bearings at the top only are the way to go with conical burrs. I'm thinking about a simple differential screw system based on 27 and 28tpi threads--you can buy 0.5 and 0.75 taps and dies. Or maybe lathe cut threads, though I don't know how to do interior threads on the lathe (super boring bar?). I'm still too worried about stale coffee remaining in the flat burrs to build the flat burr mill--maybe I'll try to retro-fit the existing one with differential screws.

I have a single plain bearing at the top to hold the cone axle in place, and a thrust bearing on the lever arm to take the axial force. Seems like wobble in the cone doesn't matter.

raj

[arriflex]

That's interesting, I was actually moving back towards a lever arm from the differential concept! As far as machining interior threads on a lathe, it's not much different from the outside. Like you said, you'll need a boring bar. Problem is when they get small, and of course it's kinda hard to see what you're doing in there! Since you're thinking differentials, it is probably easier to just use taps and go with readily available standard pitch.
I'm not sure where on the machine you are talking about using the differential. Is it going to be part of the drive axle? (think about inertia affecting your setting) or is it offset (think about linearity) or is it on the static burr?

My concept for the pseudo versa lab is starting to come together, I haven't been in sketchup for a long time though, it killed my keyboard shortcuts so I feel like I'm starting from scratch there. I envy your solid works skilz.

arri

[arriflex]

Here's a first shot at starting a model. I'll probably try to drive these big burrs with a hand crank to start off, then figure out motive power once I know how hard they turn.

obviously missing is the height adjustment, still working that out. I found a fun bearing search engine here:
http://www.bocabearings.com/

arri

[arriflex]

Raj, I just picked up a 3/8" stud from an engine block that has fine threads on one end and coarse on the other. The differential comes out to about 500 micrometers (1/2 mm) per revolution of the stud. In your experience with the robur, will that be enough resolution if directly applied?

arri

[espressme]

Anything new on these projects? yes this is a bump.
Cheers
Richard

[matadero210]

Arriflex: yes (belatedly), my screw is 250um/turn and works well. I would think 500um/turn would do as well. I never make adjustments less than 1/4 turn because its not necessary.

raj

[matadero210]

Here is the complete kit, fully working and tested. From the right:

1. Robo-Pavoni. This is a pavoni head bolted to a home-made copper boiler and brazed-steel frame. The head has been drilled to show piston pressure (dial). The boiler is insulated (kinda ugly, but not to me) with fiberglass and has an anodized aluminum spray skirt (not cleaned in this photo) in case of shooters. The PID is on the back and is normally set to 90.5C. The system is plumbed directly to my cold water house supply with a 1.7bar regulator (with no back-pressure relief). When the piston is raised, the pressure increases to 3bar for the the initial pre-infusion as the gas bubble trapped in the top of the boiler compresses. Final pre-infusion happens at 1.7bar. Typically the boiler temperature fluctuates during the pull, but since the water is already in the piston this does not affect the pull temperature. By the time the shot is pulled, the boiler is back at 90.5. System takes < 4 minutes to be ready in the morning and can pump shots until the Hetch-Hetchy runs dry. Dry-pumps can circulate boiler water through the head before shooting. I also can keep the lever raised and flux liters of water through for daily cleaning.

2. Typical shot of beans on the 3rd day. On day 1 I get way to much crema.

3. Zassen-Robur. This is a single chunck of brass milled into a hand-crank grinder. The burrs are from the Mazzer Robur, the crank from an old Zass with broken burrs, and the rest from McMaster-Carr. The adjustor screw is 100tpi on a 3/1 lever, giving 80um/turn of adjustability. Its too heavy and hard to turn for my wife but it fits my hand just fine. About 30 turns for a 1.5x shot (what Pavoni calls a double, but I use a single pull with jiggles).

4. WDT tool and naked portafilter.

5. 1.6kg stainless tamper. One side is slightly larger, for the first tamp. Tamping is done by resting the tamper on the basket filled with grist, giving a half twist, and repeating with the narrower side. The pressure comes entirely from the 1.6kg--I don't push.

6. The newest member of the team, the Roaster. The guts are from a $10 popper from target, coupled with a multi-step, ramp-soak controller from auberins.com (same as the Robo-Pavoni's simple PID controller). One switch is used to toggle fan speed (low and high speed) since the beans are larger/lighter near the end of the roast. The T thermocouple is lightweight SS jacketed and at the center of the roast chamber. The screen in the background is the chaff collector, placed over the unit in operation. Typical roast is 80g: 4 minutes between 125C and 140C, then 8 minutes ramping from 180C to 230C, for Full City. Cooling is in-place and takes just over 1.5 minutes.

Can't think of any more coffee stuff to build. Maybe a reflux still .....

raj