It was a nightmare drilling the SS piston rod. We ended to machine a new one made of ordinary steel.

Does conductivity matter that much if the tip of the probe is inside the piston? If anything, the conductivity of the brass would provide an extra heat sink to reduce the tendency to overheat.

Anyway, in practice, I found it quite easy to repeat temperature controlled shots on my two-switch Europiccola once I got the knack of it, and it didn't take long. The best and easiest method I found was to toggle power on and off and control the ROR (rate of rise). If temperature wasn't quickly zooming up and I toggled off, it didn't get out of control.

A piston rod thermowell in that case is also a much cleaner installation than alternatives I've tried.

naked-portfilter wrote:It was a nightmare drilling the SS piston rod. We ended to machine a new one made of ordinary steel.

If you use brass instead your problem is solved.

I would think steel has similar condictivity as SS. Brass would have been completely different.

Yes, but plain steel in a wet environment will give you endless rust.

It's just for the measurements Gary.

This is very cool! I imagine that if someone wanted to sell these, there would be quite a few takers around here. I bet with some tinkering it would be possible to design a very clean thermometer installation with the display sitting on top of the group and no wires running anywhere.

Thick wall SS tubing could be used. This would make the lathe work much simpler. It would be easier to match the piston to the available piston rod if required.

The area above the piston in the gen-2 La Pavoni is exposed to the vapor space of the boiler and if the group temperature is below the saturation temperature for the boiler vapor then the group will be filled with liquid, not vapor. Heat energy transfer rate from a liquid to say the piston rod will be greater than from a vapor at the same temperature.

Industrial SS sheathed long stem thermocouples or RTDs have the majority of the hollow stem packed with aluminia or silica to insulate the actual thermocouple/RTD located in the tip from the different thermal environments it may pass through. Usually there is a different (lower or higher) temperature boundary layer that has to be penetrated by the temperature probe without markedly impacting the resultant measurement accuracy.

Hi Gary -
Interesting work - kudos to you and Robert on this.

If that photo is not deceiving me, it looks like you are using it on a millennium group. Is that true?

homeburrero wrote:If that photo is not deceiving me, it looks like you are using it on a millennium group. Is that true?

Yes, that's my first lever, a Millennium Europiccola I scored on Craigslist for $50 with grinder, tamper and accessories.