I recently bought a coffee grinder with non-removable burrs (rather than a blade). The only parts of the machine that is actually of a substance that requires Tevillah are the burrs themselves. I assume that the motor is also made out of metal, but since the motor does not touch the coffee beans, it does not require Tevillah. Do the burrs need to be immersed?
There are a few factors that lead to my uncertainty:
They are made of metal - Metal is a material that would require Tevillah under the right circumstances.
They come in direct contact with the coffee beans and grind them up - This might require Tevillah as an act of food preparation.
Another act of preparation is required for the beans to be "edible" (ie, brewing the grinds) - Generally speaking, if another act of preparation is required, the owner is advised to immerse it without a Berachah. I assume this is because of doubt as to whether or not Tevillah is required. See, for example, this article advising Tevillah without a Berachah for meat grinders: http://www.kashrut.com/articles/tevilas_keilim/
The beans/grinds themselves are not eaten as food. Hot water is poured over the grinds (in the case of drip coffee or espresso) and then extracted, with the flavor, nutrients, color, etc. of the beans/grinds, or the beans/grinds are brewed in hot water and then separated from the final drink (in the case of a press). - I wonder if this would be akin to the level of preparation of clippers used to pick herbs that are used for flavoring but not actually eaten (or even eaten in small quantities), such as dill or cilantro. Do such clippers require Tevillah if the harvester/farmer is Jewish?
I am aware of the possible solution of completely disassembling the unit, removing the burrs, replacing the burrs and reassembling the unit, effectively making myself the final "builder" of the grinder, obviating the necessity to immerse it altogether. I am trying to avoid this solution, as it not only may void my warranty, but my own inexperience with this type of activity may risk rendering the unit ineffective or, possibly, dangerous.
Please cite your sources if you can.