全訳：「この研磨器具は、金やプラチナや、他の金属を荒”削り”したり、鋳肌を取り除くのに使われる」

Looks like you are having a trouble translating "reduce" and "reduction." Let's think of it this way. When you "reduce" something, you're changing the amount or the shape of something that's been reduced.
In this case, you use "polisher" to "reduce" metal. How can you "reduce" the amount or shape of metal with a "polisher"? The answer is by 削ること.

Hope this helps.

If you have further questions, feel free to contact me at <[email protected]>.