Introduction: Tamper Resistant

Picture of Tamper Resistant

Tamper Resistant is a brass and aluminum espresso tamper that indicates to the user when they’ve tamped to 30 pounds of pressure. This is important in making espresso because a correct tamp produces a better infusion. I machined the parts using a lathe, mill and other metal working tools. The bases are swappable and magnetic so that the tamper can be used with different kind of machines and portafilters with flat or convex infusers.

I did this project as part of a design and manufacturing class at Stanford, ME203, taught by Dave Beach. It's a fantastic course and introduces us to the Product Realization Lab where I now work as a TA while I finish up courses in the Masters Design Program.

Step 1: Assemble Materials

Picture of Assemble Materials

I actually designed this device with my father in mind. He loves technology and espresso and we're obsessed with pulling perfect shots. I decided to machine out of brass and aluminum so it would go with his cromed shiny home set-up.

These are the materials I used -- substitute similar materials from local suppliers. The key is to make sure that the metals acquired are machinable.

  • Steel Compression Spring, Zinc-Plated Music Wire, 2.00" L, .500" OD, .072" Wire, Packs of 6 McMaster-Carr 9657K394
  • 316 Stainless Steel Shoulder Screw 3/16" Shoulder Dia, 1-1/4" Shoulder, 8-32 Thread McMaster-Carr 97345A502 8.82 Alloy 932 (SAE 660) Bronze Sleeve Bearing for 3/8" Shaft Diameter, 1/2" OD, 7/8" Length McMaster-Carr 6381K454
  • Corrosion-Resistant Bronze (Alloy 954), Oversize Rod, Bearing Grade, 1-3/4" Diameter, 6" L McMaster-Carr 8958K666
  • 6061 Aluminum Rod, 2.375" Diameter, 6" L McMaster-Carr, 8974K57
  • 6061 Aluminum Rod, 1" Diameter, 2" L McMaster-Carr, 8974K13

Step 2: Machine Top Brass Handle Piece

Picture of Machine Top Brass Handle Piece

The top piece came together in form first on a wood lathe. I turned down modulan until I liked the geometry and curves. It took me a few tries. Then I calculated angles and machined on the lathe.

Turn down the brass bar stock according to the specifications in the drawing. Use a radius cutter to form the domed shape at the top of the handle and a zero rake left-handed tool and the compound rest to cut the angled face of the handle.

Sand the piece while it's still on the machine to get a consistent finish. Buff it and then tape the handle piece well to drill and tap it back on the lathe.

Step 3: Cut Middle Handle Piece

Picture of Cut Middle Handle Piece

The middle handle piece was tough to machine but I figured out a way to do it using the compound feed and a very extreme angle. I couldn't find a drill bit that matched my specs exactly so I had to use the boring bar on the mill to get my exact diameter.

Following the specifications in the drawing, use a left handed zero rake lathe tool and the compound feed to cut the angled face of the middle handle piece. Drill it, sand it on the machine and then mount in the mill and using the boring bar, cut the 0.850 diameter hole to the specified depth. Then drill the shallower 3/4 inch hole using a 3/4" drill. Part it off on the lathe.

Step 4: Cut the Base Flange

Picture of Cut the Base Flange

The base flange connects everything and holds the tamper together. It also allows the bolt to travel in a fixed trajectory inside itself. It too a while to design this part and make it work and fit aesthetically.

Using the lathe and the drawings, cut the flange. Drill and tap one side and on the other side, cut the holes for the press-fit magnets. using the pattern, zeroed at the center. Press fit the magnets into the drilled holes.

Step 5: Cut the Aluminum Base

Picture of Cut the Aluminum Base

I wanted to keep the base design very simple but still have it be swappable. I love the way it feels when you pull it off and put it back on. The magnets are alternating in polarity so it clicks satisfyingly into place. I also machined the convex base feeding the cross-feed and longitudinal feed simultaneously.

Cut the base on the lathe using the specifications. The compound feed set at a very extreme angle will cut the angled portion of the base. Mount the base in the mill and drill the holes using the pattern for the magnets. Press fit the magnet in.

Step 6: Thread the Bushing and Cut the Spring

Picture of Thread the Bushing and Cut the Spring

This is another connected piece but is necessary to holding the tamper together and allowing it to slide.

Thread the brass bushing and cut the spring to an inch.

Step 7: Assemble the Tamper

Picture of Assemble the Tamper

Assemble the tamper using the drawing. I realized too late that I actually had to press fit the top and middle brass portions of the tamper together so I made small deformations in the top piece that caused it to bow out slightly. I then press fit it into the middle piece so that they effectively acted as one piece.

Comments

Breck Lewis (author)2015-10-08

I'm really impress with the tamper resistant that lets me know when I have tamped 30 pounds of pressure. I love making espresso every morning before I take off to work. I've used other similar devices before, but they don't seem to be as good as this one. How much does this device cost me? <a href='http://www.pacmet.com/index.php?h=capabilitiesandservices' > http://www.pacmet.com/index.php?h=capabilitiesandservices</a>

epaulson2 (author)2015-02-12

I might do this but with wood

PhilTee (author)2015-02-12

Wow! This looks amazing, I wish had the skills to build one. Really nice work - well done!

seamster (author)2015-02-12

Your video is blocked with the message "This video contains content from SME, who has blocked it in your country on copyright grounds."

I'm curious how this actually indicates when you've hit 30 lbs of pressure. (Is that bit of info hidden in the blocked video?)

davidbordow (author)seamster2015-02-12

Sorry to hear it's blocked in your country. I'll see if I can fix that.

The tamper indicates it has hit 30 lbs of pressure when the gap between brass and aluminum closes (about a 1/4 inch gap). You can both feel it under your hand and see it close.

seamster (author)davidbordow2015-02-12

Cool, thanks for the explanation. I wondered if it just "bottomed out" and that's how you could tell. Very clever!

If you're in the Bay Area, we're in the same country--and pretty darn close too! :)

(I think the SME block has to do with music? I'm not sure though.)

tomatoskins (author)2015-02-12

This looks great, and I'm sure it tastes great as well!

crank_girl (author)2015-02-11

Great 'ible. Really professional finish. You could sell these.

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