I designed this calibrated espresso tamper to deliver precisely 30lbs of pressure when the handle cap is completely compressed along the hexagonal running shaft of the base, though the pressure you achieve will vary depending on which spring you use with it. The design maintains the spring in a small amount of compression at all times so that the tamper is slightly pre-loaded to avoid loose parts making noise.

Operation:

Once assembled, use the tamper to compress your ground espresso within your portafilter. Stop applying additional pressure once the cap of the tamper is compressed as far as it can be (a few millimetres above the top surface of the tamper base).

External Parts:

The only non-printed part is the spring that is used to calibrate the applied load. I based my calculations for the compressed load off of a 302 Stainless Steel Corrosion-Resistant Compression Springs, 1.375" Long, 0.563" OD, 0.419" ID, with a stiffness of 47.44 lbs/in from McMasterCarr (https://www.mcmaster.com/catalog/127/1399, part number: 1986k124).

Print Instructions:

I printed the Cap, Retaining Nut and Spring Supporting Nut all from PLA using 3+ perimeters and 15%+ infill, with an infill boost to 20% for the threaded section of the cap.

The Tamper Base was printed in PETG using 2+ perimeters and a general infill of 20%+ with an infill boost to 60% for the area where the hexagonal piston emerges from the tamper base. It may also be worth increasing the number of perimeters and infill around the top threads, as I had one fail there after about a year of use.

Note on Base/Portafilter sizing: I have included several tamper base sizes to accommodate many of the standard portafilter sizes. Each is slightly undersized to allow the tamper to easily slide into the portafilter during grind compression. The smallest size (39.4mm diameter) fits the Flair Espresso Machine.
Enjoy! And please share your makes!