A few days ago my wife and I visited some friends in the country. On one road there was a sign warning of log trucks. If a log cabin is a cabin made of logs, then a log truck is likewise a truck made of logs. Ummm, no … it’s a truck designed to transport logs. In fact, in some parts of the English-speaking world, such as Wikipedia, they are logging trucks, which term I had never consciously encountered. Compare a wooden truck, which is (?toy/model) truck made of wood, and a wood truck, which is a truck designed to transport wood.
English allows the modification of a verb by another verb, which I would call a noun modifier but which Wikipedia calls noun adjuncts and The Cambridge Grammar of the English Language calls nouns as attributive modifiers (p 537). The two nouns can have a wide range of meanings, but neither of those sources has a comprehensive list. Most of the time we have no difficulty understanding the meaning, but there is ample scope for ambiguity, eg a brick factory. (A glass house v a glasshouse (greenhouse) raises another issue, which I won’t go into.)
Some sources classified or classify noun modifiers as adjectives. They’re not – they can’t do adjective-y things like being further modified by very, making comparative or superlative forms or forming adverbs: *a very log truck, *a logger truck than the previous one, *the loggest truck I’ve ever seen, *The truck drove logly.
Never Pure and Rarely Simple 
Other English phrases that might confuse the learner include “coffee cake” and “garage sale.”
This is why French makes the distinction by means of a choice ofpronouns: “de” vs. “à”. For example, there is a big difference between (to use a bad translation of “coffee cake”) “gâteau de café” and “gâteau à café”; one is cake made of coffee and the other is cake intended for use with coffee. I find this feature so useful that I even tend to apply it in English to clarify an otherwise ambiguous noun adjunct.
It is often a source of amusement to me in a hardware store (a store that sells hardware, not a store built of hardware) to see hand sanders. Are they for people with rough hands?
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I wasn’t familiar with coffee cake, but my older female relatives used to eat tea cake. Koreans eat green tea cake, which is a taste I haven’t acquired yet.
I also thought about cakes of soap, which are basically soap. Google shows me that soap cakes are either soap which looks like a cake or cakes which look like soap. One of the those should possibly be a cake soap (compare also a soap of cake). I’m confused now.
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