sanding out scratches

[alpinelakespilot2000]

While deburring the corners of a HS spar doubler, the deburring tool slipped and scratched the surface of the doubler. Not deep, but a scratch that I have since smoothed out almost entirely with just a little scotchbrite pad rubbing.

That said, I still see a very faint straight line (the remants of the scratch) underneath the scuffing left by the scotchbrite pad--although my finger can't feel it when I run it over where the scratch was. I've decided to get it out the rest of the way--should I just continue to use the scotchbrite hand pad (and press a little harder) or is there another abrasive, maybe one step coarser, that I could use first.

I've probably fretted about it more than I should have (this is my first "mistake," except for drilling out two skin/rib holes in my VS at #30 rather than #40), but I know that stress can concentrate on/in scratches, so I don't want to be left wondering about how my HS spar doubler is doing while at 10K feet! Better to have it over-prepped before priming rather than under-prepped!

Thanks,
Steve

[TShort]

I've been wondering a similar thing - the instructions for the rear spar doublers on the -8 say something like "polish to a satin finish equivalent to that left by 400 grit wet/dry sandpaper"

Any reason why this is more specific than other prep areas? After clecoing them in place to drill other holes, etc, there are scratches from the metal shavings - do I need to buff these out?

Thomas
-8 Empennage

[Derrell]

On the "From The Ground Up" series they said to use sandpaper to remove the scratches. This has worked for me pretty well. You can then come back with Scotchbrite & buff the part.

Derrell
7A Finish

[AlanB]

I think it kind of depends on exactly where the scratch is. The idea is to keep scratches and notches away from an area that goes into tension, such as the edges of the doubler. Even a small imperfection in a highly stressed area can lead to eventual fatigue failure of the part. If the scratch in near the center line of the doubler or out near the tip end where the stress is low, I wouldn't worry too much about it. If it runs laterally across the edge you were deburring then I'd sand it out. Especially if it cuts into the corners. Just my 2 cents worth.

Alan
RV-4