Instrument for tramps to scrape off edges (4)

I believe the answer is:

oboe

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'instrument' is the definition.
(type of musical instrument)

I don't understand how the remainder of the clue works.

(Other definitions for oboe that I've seen before include "Player" , "Orchestral piece" , "Double-reed wind instrument" , "Woodwind instrument of treble pitch" , "issuer of notes" .)

I've seen this clue in The Irish Times and The Guardian.

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