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

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

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

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

Just awesome.

Hi Matadero,

hope you are still around. Just a quick question, as I am also thinking about building a hand grinder with big conical burrs: How did you mount the inner burr for the shaft? Did you just use a threaded shaft and 2 nuts to hold it in place? Or was something more complicated involved, in order to avoid that the burr turns on the shaft?

Thanks in advance,

Roland