How to Build a Thermofilter

The first step is to seal the bottom of the filter basket with a thin layer of JB Weld, leaving only a hole which will allow a flow of approximately 50 ml/25 seconds.

Starting with a single basket, a wire will keep a small opening in the bottom of the basket. The single hole will allow a flow of about 50 mL per 25 seconds. To do this use a 0.011 inch wire.

Coat the wire liberally with silicone lubricant spray and allowed it to dry. This is so epoxy used in the basket not adhere to the wire and allow the wire to be pulled back out.. Insert the wire through a hole in the center of the bottom of the basket and tape it in place so that it is vertical.  About 1/16 to 1/8 inch of JB Weld epoxy should be layered in the bottom of thebasket and will hold the wire in place. It should look something like this photo.


When the epoxy is fully hardened pull the wire out, coat it with more silicone and reinsert.
 
The next step is to place a short piece of simple plastic drinking straw around the wire. This will become the pathby which water exits the hole.

It should look about like this after the first JB Weld mix. 

This is the JB Weld you want to use:

 

Let that fully set/harden, probably overnight.  You can get some leveling of the JBW if you warm it until it thins a bit. 

When The JBWeld  is fully hardened, pull the wire out the bottom.  You need to be able to re-insert the wire if a coffee ground plugs later, so keep it on hand.  It will probably take pliers to grip for pulling the first time. 

Note:  It you cut the wire on the end that goes through the epoxy the wire cutters will slightly crush and flatten the wire, and you will need to deburr it so that it is round.  You can hold the end of the wire against a Dremel sanding drum or grinder and turned the tip slowly.

More notes:
I made a loop at the bottom end after discovering in a previous attempt how very hard it can be to pull out.  Then I used needle nose pliers and wound the loop and the wire around them before pulling.  Also I had applied silicone a couple of times and sharpened the end of the wire.  It worked.
In the pictures you can see that the basket is supported on the rim of a short glass.  The loop of the wire and a bit of blue tape are supporting the wire so it doesn't just fall back out.  It took a bit of fiddling to find the right depth, but if you just put the basket into the vise the wire will ....slip slide away....

The following photo shows hole placement.  (The ink dot is where you don't want the hole). That hole was drilled with a 3/32 inch fresh sharp drill. You may need to make a slight indent to get the drill started. A vise helps for holding the basket.
See the deburring tool?. There should not be sharp edges at the basket edge.  Toothpick shows the approximate thermocouple path and elevation at the "puck" center.
Here you can see that some of the Teflon and insulation have been stripped back to give a bit more bare wire.  The JB Weld nees to adhere to the wire and seal off the insulation and Teflon.  The thermocouple was also formed to a smooth arc to help stop bending especially at the basket edge. 
That picture with the toothpick shows the hole in the strawis a bit too high, but that was one of the easiest adjustments in the whole build  I just pulled the straw out and scissored a bit off the bottom.  When I re-inserted the bead of the TC after that it was more horizontal.  Even then  it was a close call when I did the next pour;  the wire was in danger of being exposed if I kept the pour below the rim of the straw.
 
The height of the "puck" is fairly critical.  It you make the puck low, you have too much sitting water and then not good thermofilter response.  Too high and it will hit the screen and not work at all.  You will want the thermocouple and bead at about the ridge height, or probably just below.  Adjust the straw height and bead hole in the straw accordingly.  Also, spread the wires a bit and form an "eye."  The eye can lay horizontal and then the TC make a smooth arc to exit. Also note that there is the central 0.011 wire coming up out of the straw.
 
When all is taped and held in place, the final batch of JBW can be mixed and "poured."    You can heat a little to help pour, and then heat the basket to help level and smooth.  A heat gun and OVE gloves are most helpful.

 

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