The WMF Kult milk frother is a manually operated device that rotates the whisk via an up and down movement and thereby froths the milk. The principle of operation is similar to that of a humming top. In the hand grill there is a sleeve around which helical grooves wind on the inside, like a screw. On the central shaft is a counterpart that grips the grooves via four grippers. When the handle and thus the counterpart are pressed down, this moves the shaft. The mechanism is reset via a spring.
The counterpart with the grippers is made on softer plastic and apparently wears out a lot over time. I completely disassembled the milk frother and redesigned and 3D-printed the counterpart as a replacement part.
The stainless steel sleeve on the handle must first be removed. This is glued and must be removed by carefully heating it with a hot air gun (Fig. 1). Then pull the shaft and black guide sleeve apart. The white gripping piece is firmly glued and must be removed by slitting it sideways (Fig. 2).
Because of the high mechanical stress combined with the small component size, I produced the replacement part with a resin printer. I used the Formlabs Form 3 with Rigid 4000 resin (Fig. 3).
The spare part has an oval opening that must be pressed onto the shaft with a lot of force. In my case, I hit it with a soft-face hammer. Once the correct fit of the part has been checked, grease the grooves of the black guide properly. Fit the spring onto the white counterpart (Fig. 5). Apply glue, preferably 2K epoxy resin glue, to the black sleeve and put on the stainless steel sleeve. Done (Fig 7).