I started modding a Gaggia Classic with a PID and wanted a thermofilter to measure changes. I looked at various DIY models and the Scace. I did not want to buy an extra PF and basket just to use it for the start of a thermofilter. I first tried a PF device made from HDPE that fit the PF spout. That was interesting but had a lot of extra dead water space. I read about filling the space with wrinkled aluminum foil. It tends to trap air and fills the space without much density. That seemed better but was messy and not fun to use. I eventually settled on filling the space with HDPE. It has little thermal activity and fills the dead space. Others have noted plastic and epoxy, often hardened into the basket. I do not use a basket at all. The 1/8th copper tube is my “probe” and I have used a K thermocouple for measurements. Before using the K thermocouple I used a Polder digital thermometer. The wiring and thermistor are easily removed from the stainless probe and then 26g – 30g wire can be spliced in to lengthen the thermistor to electronics distance. An over sleeve of silicone tubing acts as a seal.
I am interested in others comments and in seeing what others have done for a home, DIY thermofilter. Perhaps a place to collect information for others to use. I have a friend with a lathe who did the work as I designed it. The Probe piece was made a few months ago. I was not happy with it, but it took a while to decide why, and try to solve the problems.
HDPE gets slightly soft and expands at about 160F. The probe initially quit leaking and became a plug. I thought that it was too tight in the hole and made it loose, still a stopper. I finally found that it was just malleable enough to fit the bottom of the PF too well. Literally 2 surface scratches and a little trial and error give about 50 ml in 25 seconds. HDPE is cheap, lathe work is not, unless you have a friend or a lathe.
Aluminum foil filler works but is messy, the HDPE puck is great. A slide in fit that completely tightens with heat and has to be cooled to remove. It leaves only about 5 ml, or less, of water after the 3 way empties the PF.
The silicone tubing works great to keep every thing dry. Unfortunately the shrink wrap over solder joints on the Polder keep me from using a long piece of silicone. I use a 8" piece on the K thermocouple and have silicone tubing from the bottom out of the cup that I use to collect the "double."
Hooked up and used here, though you are seeing the result on the Gaggia, not seeing the thermofilter.
Cool idea, you're lucky you have a machinist friend.
When I was using a Classic, I just used 30 guage TC wire, and ran it over the lip, letting it sit on top of a puck. This has a couple problems, every time you do it, the TC end will be in a slightly different spot. Also, the wire eventually breaks where it goes over the rim of the PF. But its a cheap and easy way to read PF temps, you just need 30 guage TC wire (I used type K) and a temp meter.
Now I have an Expobar Office, and have a TC in the grouphead, so I can read the grouphead temps as I flush. At some point, I measured the PF temps, and figured that there was a 5 degree difference between grouphead and PF temps.
I would be nice if someone could figure out how to make somethink using a basket and maybe epoxy or something to fill the basket, but flow control would be difficult to manage. Most people don't have access to a machinist ;).
I will thank Randy for the idea to build a simple basket thermofilter, and no machinist. I found some nice baskets for my Gaggia and decided to donate one to trying to make a basket thermofilter.
First I duct taped the basket shut and made one hole through the duct tape. I got about 45 – 50 ml flow. I tried to determine hole size and was not precisely able. It is smaller then the 0.015” diameter wire that I had. I found a friend with a “guitar string” of unknown size that fit. It was 0.011 wire, to micrometer, and the hole seems perhaps slightly larger.
You need a piece of wire to keep a hole open in the basket and the wire must have the strength to be pulled out. 0.011 music wire, an “E” string, if I read it correctly. My KS hobby music wire, readily available, does not go below 0.015, so find a music shop, or guitar friend.
I wanted the probe central, and after I saw the stream, jet, from the single hole, I decided to put it slightly away from the probe, and to have it spray on the bottom of the PF before exit. Now there is a regular flow, not a jet spray.
I had access to HDPE and that is my puck. HDPE is used as common cutting board. I have a plastic and fiberglass shop nearby. Scrap was very cheap. I could only cut about 1/4” through before it got quite hot. I cut 1/4” through each side of the 1/2” HDPE. It was a rough cut with a 2.5” hole saw. The central piece is the puck, dressed up with a drill to spin it against a sander. The 2.5” hole cutter used a 1/4” central drill pilot hole making the cut from each side align and providing a hole for mounting to drill or drill press. You have to reduce and shape the puck to fit the basket, slightly loose as it will swell, but not too loose or it will allow more dead space. You also have to shape the bottom edge to fit the basket.
The probe is 1/8” copper tube available at hobby shops, or use brass tube. Copper is much more heat conductive and better. I soldered a washer on it to set depth. Determine depth by drilling a 1/8 hole in the basket and then put the basket in a PF and insert the tube to find depth. Solder the end shut and solder the washer.
Silicone tubing to keep the sensor dry is from a hobby shop. Radio Control and fuel motors use it, DuBro is a common brand of fuel tubing. Noted in first post.
JB weld the bottom of the basket closed, and the tube in, and the wire through your chosen hole. If you use a thin layer, about 1/8” then you have room above for 1/2” puck. This means that the copper tube is just over 1/2” inside the basket above the washer. I relieved the puck bottom about 1/32” so that there was a “path of least resistance” for the water. I wanted the water to go down the center around the tube and exit the hole, not go between the puck and basket.
I used contact cement, rubber cement, and contacted a piece of med fine sandpaper to the bottom of the puck and then inserted the puck in the basket and lightly rotated it to that the slight rises of off the JB Weld in the basket. The flattened areas are slightly dull and light colored in the photo. Probably not necessary, but took a little “rocking” out of the puck and will keep dead space minimal.
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