Every time you drop your knockdown you are scratching the tip. Keep some 400 and some 1000 grit sandpaper close to you all the time. (on your cart or in your bag) Whenever you drop your knockdown sand out the scratches. (start with the 400 if the scratches are deep)
If you want to get really serious, finish the knockdown by rubbing it on your shoe leather, for a perfectly smooth finish!