I played around with the machine today and learned some interesting lessons.

I tried the soft copper as a gasket material and it was a complete bust. I ended up using food-safe (red high temp) RTV between the copper plate and the group head. It seals well, seems to transfer the heat well enough, and doesn't impart any smell to the water. I was careful where I applied it to keep it mostly out of the water path.

When the boiler is up to temperature the pressure is higher than my water line pressure so I can't fill until I bleed off all the pressure. I installed a check valve in case this might happen and it looks like it was necessary.

I am measuring the temperature of the group head at the bottom of the section between the flange and the cylinder. I am using the PID to control the cartridge heaters in the copper plate and it works fairly well. There is a fair amount of lag from the heaters to the measurement point but it seems to be okay. I've sandwiched a screw-eye thermocouple between the group and a hose clamp and it's a very good temperature measurement.

I've installed another screw-eye thermocouple to the bottom of the boiler where there was a boss with a threaded hole (it was used to install the boiler to the machine's base) and it works fairly well. As the water level lowers the steam actually gets much hotter than the boiler water temperature. I don't quite understand how that works. For my purpose, controlling the boiler water temperature is appropriate because the dipper tube directly sends water from the bottom of the boiler to the group head. I just need to watch the sight glass once I get another tube .

My theory for this machine was that by controlling the heat of the group head and the boiler water temperature I could have a much smaller differential between the two and get good brew temperature control. After experimenting with different temperatures then actually brewing espresso I found that my theory turned out to be true. I'm now running a group head temp setting of 205 degrees and a boiler water temperature of 210. I will probably experiment more to dial it in further but I'm pretty pleased that within 90 minutes of getting the PIDs hooked up I was able to brew tasty espresso.

I'm running the shot until I get a 50% brew ratio then I move the shot glass out of the way and let the shot run. It visually gets lighter after about 1.2 ounces so it does go blond. I get some portafilter sneeze after each shot. I'll need to work on a better post-shot routine.

All in all, I'm pretty pleased with how it turned out.

Here's a bad video of the first reasonable shot. It's from a fresh-opened Illy medium roast beans so there is very little crema.
Edit: after experimenting with a bunch of different temperature settings it's become apparent why this shot looked burned but didn't taste awful. The group head seems to be quite forgiving. The hotter the water gets the faster the heat bleeds away from the group.

Looks like you are brewing with boiling water from the steam coming out of your P/F spout. Also you should be able to pre infuse (lever down) for at least 4-6 seconds before you see any drops if you've got the grind dialed in.

I assume you know more than me but i have to ask...if your group is 205 and your water is 210 wouldnt the water have to over the 205 maximum ideal temp threshold?

Also, i wonder, as the boiler losses thermal mass and the water evacuates, is it possible that the temp drops slightly, kicking in the elements, but then the thermocouple lags and brings the water to a boil?

Those are interesting comments, thanks. I will have to do some more experiments to get a handle on the thermal behavior.

pizzaman383 wrote: When the boiler is up to temperature the pressure is higher than my water line pressure so I can't fill until I bleed off all the pressure. I installed a check valve in case this might happen and it looks like it was necessary.

Sounds like your line pressure is really low? At 1.5 bar boiler pressure or so I would figure most city water line pressures should be much higher. Or are you on a well system?

Overall I thought the shot started out pretty well, but it does seem like maybe the cylinder didn't fill completely.

I see you're using a PID to heat the group head, but how much does it heat up over your 205 after a shot and how long does it take to cool back to that temp?

Very interesting design, and I think with some tuning and gathering data, you'll be pulling amazing shots one after the other. From experience...I know this can lead to very caffeinated sessions!

I think I need to rework the temperature sensor locations. The temp sensors are below the boiling of water but there is clearly stream present so something isn't working as it should.

It turns out that the location I chose to measure the boiler water temperature reads 50 degrees lower than the boiler water temperature. That was causing the boiler temperature to be in the 270 degree range when I thought it was 220.

After changing the boiler temperature sensor to the top plate of the boiler the machine behaves something like the Strega and Prestina. I can now start dialing in the settings for real coffee by taste and I can work out how long between shots gives consistent shots.

Edit: it turns out that the case was touching the boss where I attached the thermocouple so I was measuring the average temperature of the boiler and the case.

Finally, I'm pulling good shots! I played with the group head temperature and boiler water temperature set points to get close by measuring the water coming into the portafilter then made the final temp adjustments by tasting the espresso. For now, I'm running the boiler temperature at 240 degrees F and the group head around 200 degrees (that's achieved by controlling the copper plate to 210 degrees).

Those Italian designers know their stuff as when the temperature is in the right range the group head makes it all work out right. The group head cools back down to its idle temperature after about a minute so my normal shot prep routine will work.

Here's another bad video. I rushed it because I wanted to drink the espresso shots I just pulled! This is Klatch House Decaf espresso and it's one of my go-to favorites. There seems to be more crema than I get from my Vibiemme DD E-61. Tomorrow, I'll do equivalent shots to compare the two machines.

To get around the portafilter sneeze, after the shot I leave the portafilter locked in until after I've prepped the next basket. That gives me a very nice, dry puck that pops out easily.

http://youtu.be/qrbOXa9AkC0

Now, I need to mount the PIDs and clean up the wiring. I've got two PIDs doing the temperature control and a third that displays the group head temperature. I'm going to try it with the open look first to see whether I need to build a case or not.

I also need to by another sight glass since I broke the Pavoni spare when I tried to shorten it by 1/4 inch so that it would fit. Does anybody know where I can buy cut-to-length glass tubing?

You still need to tighten up the grind as your shot is pouring way too fast. The most you should see is a drop or two, if that, with the lever locked down for 4-6 seconds. The water is running right through your puck. Get the grind right & you will see some real crema & your shots will taste much better.