My interest in hand grinding beans for my coffee has lead me into a land of myth, anecdote and folklore with little hard data to support what, if any, manual grinder is worth owning to use on a daily basis.
Most people with opinions buy one on eBay or from a thrift store that may or may not be in very good shape and add a bit of information that may or may not apply to every old coffee mill from the same manufacturer. Even the best brand will not grind well if the adjustment is off or the mill is simply wore out from fifty years of use. Not one to break with tradition though, I will offer my own piece of anecdotal data regarding the Zassenhaus knee mill I picked up recently on eBay. Here (with some editorial house cleaning of the Google translation) is some background found on their web site:
"Since its establishment in 1867, Zassenhaus has met the highest standards in functionality and for quality of it's products. Their high-quality products always are ahead of their time. The independence of Zassenhaus is considered one of the company's success factors too. This small company can always respond to changing market situations without leaving their traditional values. The roots of the company are in Schwelm, but have shifted over the years to Solingen."
The story I found shows this company started as a machine shop producing gear shafts for iron works in 1867. The burrs are similar to a gear shaft, so going from that type of production to making coffee mills is not such a stretch.
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The wood on my grinder (and matching handle knob) is very dark and might be walnut, but I am not sure. These are not thin pressed planks either. Most pieces are almost a half inch thick giving the box some heft and a very solid feel. The grounds drawer is also wood and is joined with dovetailing (craftsmanship found on a part not visible most of the time is noticeable due to it's rarity in modern manufacturing).
The grind size is adjustable by turning a large, grooved, step-less adjustment nut found right below where the long steel handle meets the top of the center shaft. The steel cover for the bean hopper is thick enough to prevent flexing and provides a good base to handle the torque created by the handle when cranking the inner burr drive shaft. This shaft is thick and short which prevents much if any wobble and keeps the movement smooth as well. The inner bean tray located above the burrs is coated with a cream colored enamel (this is another nice touch since it is not viewable while using the grinder). The burrs are machined from steel and have many sharp teeth.
The one sore spot with this grinder is the use of a plastic burr stabilizer instead of a metal strap but so far this hasn't given me any problems and the grid size is very consistent for espresso all the way to drip. Would I buy it again? Sure, especially since the price I paid for this used mill seemed very fair to me. Since your mileage may vary in the second hand market, I would suggest looking for a new model as the easiest way to ensure satisfaction. These are available new for $80 - $100 online which is not inexpensive but considering the level of craftsmanship, these mills provide a value equal to the price.