I have built, using a juice extractor from Amazon.com ($20.00) and the idea from Richard (Espressme) a cheap and effective autotamper using my Solis SL70 (53mm) portafilter.
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The base is plexiglass or acrylic which I obtained from a plastic supplier for free. They had a "cutoff" bin of scrap pieces that I got. I measured using calipers, the outside dimensions of the Solis portafilter, marked the plexiglass and using a bandsaw, cut out the "U" shaped pattern. After drilling a hole for the vertical column, I drilled and tapped a 1/4 20 thread in the back and front of the hole for the vertical column. I then inserted a 1/4 20 thumbscrew and a setscrew so the column would be held by both screws (the thumb screw by itself won't work, you need an additional screw in the front since the the plexiglass platform takes 30 lbs of pressure from the tamper.
I took my commercial tamper apart and in the steel base, tapped a 1/4 20 thread. I also tapped a 1/4 20 thread in the brass male plug. I then took a 1/4 bolt, using a cutoff wheel cut the bolt to about 1/2" length. I screwed the brass plug onto the bolt sticking out of the steel tamper. The brass plug screws into a copper female fitting as seen in the photos. A small section of thick walled brass pipe slips into the female fitting. I drilled and tapped a 8-32 set screw in the copper tube and the female fittings. Be careful when tightening the set screws, use moderate pressure or they will rip the threads out of the brass pipes.
I place the portafilter on the plexiglass platform and adjust the platform where the tamper is just above the portafilter basket. I then tighten the thumb screw and the setscrew. After dosing the portafilter with coffee (for the Solis, I use a 14.6g dose). I then take the handle and press down on the portafilter until the spring bottoms out (It also works when the handle on the juicer is moved where the spring compress 1/2 way). My shots are 28 seconds and I am getting about 2oz per double. The crema is 1/4" thick and sumptuous. I would suggest that some experimentation take place for you to decide what height the platform should be at. You will have to try various heights, pull a shot and see what adjustment on the platform will give you a 2oz shot over a prescribed time...a little trial and error.
The spring at the top of the unit is 1" long. Hardware stores don't sell the springs based on the number of pounds. I bought several, took them home, placed them on my bathroom scale, put a board on top of the spring and pressed down, choosing the spring that gave me about 30 pounds of pressure. Trial and error here too. The top cap on the vertical column was removed and the spring that came with the unit was thrown away. I cut the bolt that holds the top cap on to about 1/4", placed the spring on the vertical column, placed a very large washer over the bolt and screwed everything down.
I have to thank Richard and his original idea that got me going on this project. Sure beats $400.00 for the commercial units!
