Scarf joint

[Captain_John]

Hey All.

Question for ya...

When scarfing the top wing skins, is there any harm in doing the whole joint... all the way back to the trailing edge?

Dan did just the front corner where it meets the tank skin.



I was thinking it would be a better transition to lightly do the whole length of the joint. Anyone elso do it?

Pro's... con's?

CJ

[rv8bldr]

Hi CJ,

Well, you could go to all of that effort, but I don't think it will buy you much in the way of aesthetics. I did the scarfing for 2-3 inches and it looks great. Unless you are specifically looking for the joint, you don't notice it at all.

Just my $0.02, and even then is probably WAY over priced ;-)

Cheers

[Captain_John]

Cool, just the corner it is!

Tell me your method for shaving the material off. The instructions call for filing it. Kinda vague, really.

I was thinking about the aluminum oxide 36 grit roloc pads to start with and transitioning to finer scotchbrite as I get closer to the desired level.

Seems to me that the 1/4" die grinder would be the best way.

CJ

[rv8bldr]

I think I used a vixen file to start (to get most of it off), then transitioned to an orbital sander (a couple of different grits of paper), then finished it off using the scotch brite wheel to get the fine scratches out. Although it has been several years since I did it, I don't recall that it took very long.

That's it. Hope it helps !

Cheers

[Captain_John]

It does!

Thanks!

CJ

[RudiGreyling]

Hi CJ,

I'm with you on this one, the instructions are not too clear on what to do here...A Search on the web returned only 1 useful hint see text below...

1) Do you guys do both skins? i.e Top of inboard and bottom of outboard skin?
2) Do you prime the areas that was filed, or just use an alodine pen.
3) Any other advice...before I take a file to my pretty skins?

Thanks
Rudi

Originally Posted by google search

I just did this last week and this is how I did it. We clecoed the skins in place and scribed a line with a needle on the inboard skin where the edge of the outboard skin ended. We pulled the skins off and worked on the inboard skin. We clamped a straight edge along the line we just scribed, to keep from damaging the part of the skin that we later be visible, and then took the rasp and started filing. We worked from about 3 " from the leading edge forward, until we removed metal down to the spar holes and had a nice angle leading into it. The top skin required no alteration, and the fit to the tank skin was perfect. Hope I explained this well enough.
Phil Knox

[Captain_John]

Thanks Rudi!

I still have yet to do this, but the extra time on learning is a good thing.

I can now broaden my scope of tasks with the tank duties now all laid out in my mind's eye.

Re: Scarfing, it seems also that removing some material from each side is prudent. I plan on removing more from the lower skin than the top one. I still plan on using my roloc tool in the die grinder with oxide sandpaper attached and finishing it off with scotchbrite. I am expecting that the sandpaper may be aggressive, but I will practice on some scrap first.

Are you getting ready to do this soon too?

CJ

[RudiGreyling]

Originally Posted by Captain_John

Thanks Rudi!

I still have yet to do this, but the extra time on learning is a good thing.

.....

Are you getting ready to do this soon too?

CJ

Yes It is a toss up between the wing skin scarfing and prosealing the tanks at this stage, both scare me still...that is why i am asking for more information on the scarfing! (there is a lot of info on prosealing the tanks though!)

Anybody have some more input please share...

Thanx, Rudi

[RV7ator]

C.J.,

Keep your hands off the power tools for the scarf joint, lest you scarf it up.

I just finished my eigth joint (second airplane), each takes less than ten minutes with a file. They are flat, even, smooth. The trick is using a big, flat mill file with a safe edge, then a smaller edge cutting file for dressing the fillet. For milling, the wider the file the better, and in the proper reflected light you can easily see the plane left by each stroke so you can make adjustments as you go. Mark the cut line with a piece of masking tape; it sits proud and won't get hidden by shavings as a marked line will.

(Files cut one way - pushing away from you. Don't saw, your arm's joint articulation will make a curved line. My tool-n-die maker father could file a part to shape so well it looked like it was machined.)

Set the edge even with a flat table top and stroke from edge to center of the material. Other way around your knuckles raise the file at too obtuse an angle. The exercise is not to hide the joint, but remove .025 from the leading edge of the .032 inboard sheet to lower the .025 outboard sheet's leading edge even with the .032 aft edge if the tank. (10 knots worth less drag!) Prettiness comes from even, straight lines. Gap width, constant gap width, isn't as important. (True of any joint - wait until you get to the cowl!) The length of the scarf area I make about an inch; more doesn't enhance anything and makes maintaining a straight line more difficult. Use the small file to cut the fillet. Dont' try to make a square notch - that's a stress riser. Instead slightly radius the under side edge of the top sheet to snuggle into the joint. Scotch-brite and spot prime.

I caution staying away from hand held power tools because they are nowhere near as controllable, in an instant can remove too much material from the wrong place (this is thin stuff you're working with and your target is only .007 thick), and this fine work requires finess, not horsepower.

Captain John (another one!)
Siebold World Airline (That's right, singular.)

[LettersFromFlyoverCountry]

I did mine with the skins on...Just a Vixen file....took the top off the inboard...and the bottom off the outboard. Bend back down, evaluate, repeat.

Clean up with 400 and 600 grit. Shoot some primer.