Making a thermo-filter

I’ve been making a thermo-filter, like a SCACE device, to make sure that my machine works as well as I think it does. Up till now, I’ve just been pushing a thermocouple up into the group-head outlet pipe, but this does nothing to control the flow rate or mimic the conditions inside the filter basket.

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I’ve made the plastic puc from acetal, turned down on the lathe, then drilled and tapped a hole in the centre. The acetal turns really nicely, and the thread feels very strong.

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I made the bottomless porta-filter earlier on my milling machine. The valve is a needle valve from eBay, which will enable me to control the flow rate and mimic different extraction times.

I have a bare-wire thermocouple to take the temperature measurement. They respond much faster than enclosed-type thermocouples, as the heat does not need to be conducted through the probe shell. Considering the extraction is over in about 25 seconds, if it takes the thermocouple 5 seconds to respond it won’t be a particularly revealing test.

I’ll fit the probe later. I’m away at work now, so it will be a couple of weeks before I can make sure it fits my machine and glue the probe in position.

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