Scarf joint

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

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

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

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

It does!

Thanks!

CJ

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

google search said:

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

Click to expand...

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

Captain_John said:

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

Click to expand...

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

Armstrong Tools

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.)

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.

Thank you gents!

I appreciate it! After all, these are hand built airplanes.

...and John, we also share the same initials! JS!

Rudi, don't fear the proseal!

CJ

My two cents...

If you want to lose sleep, lose it over the tanks, but don't lose sleep over the scarf joining. Slightly taper the edges Van's suggests you taper (top of lower skin and bottom of upper skin at the corner only) and move on. You are only trying to make that double layer where it meets the tank skin slightly less obvious. You are never going to make that seam/joint disappear. It took me about five mintues with the file first, then cleaned it up with a scotbrite wheel and then finally a scotchbrite pad. Primed that area and I'm done. One thing I would highly recommend AFTER the scarf joint is to use your edge former/roller (especially if it is the Cleaveland variety). That will do more to make that seam disappear than the scarfing will in my opinion.

Good luck.

Hi Guys,

Thanks for the excellent advice.

I need to get this clear and I want to do it right so please be patient, I have some questions on the suggestions:

RV7ator:

...The trick is using a big, flat mill file with a safe edge, then a smaller edge cutting file for dressing the fillet...

Click to expand...

What is file with a safe edge? And what is a fillet?

alpinelakespilot2000:

...One thing I would highly recommend AFTER the scarf joint is to use your edge former/roller (especially if it is the Cleaveland variety). That will do more to make that seam disappear than the scarfing will in my opinion...

Click to expand...

I have one since I bought the Cleavelad RV toolkit, but on which edges do I use it on the scarf joint? Typically where else do you use it?

Thanks in advance.
Kind Regards
Rudi

RV7ator said:

I just finished my eigth joint (second airplane), each takes less than ten minutes with a file...(snip)

Click to expand...

John, this is a great description of the process...any chance you have some pictures, or even a link to some pictures, that you could post?

Thanks,

Dave

Files

Rudi and Dave,

Sorry, no pix, and I don't know of any posted examples.

A fillet is the material transistioning between two faces that makes the material's cross section a bit bigger at the intersection. The inside radius at the vertex of angle stock is a fillet, for example.

A safe edge file is smooth on its side(s) between the two cutting surfaces on opposite faces of the file.

Somebody mentioned turning down the edge a bit. That's good edge cosmetics, but it's not a replacement for the scarf joint. You'll really want to turn the edge of the aileron nose metal when you get to that joint. Otherwise, it sticks up like a cheese grater.

John Siebold

File The Inside Of Each Skin

If you are going to do a polished aluminum "paint job", do all the filing of the skarf joints on the INSIDE of each skin. I have and it works great. The method is the same as already described. IE, Vixen, then finer grit paper or roloc pads. Afterwards, there is nothing keeping one from slathering on plenty of alodine or primer or whatever corrosion cocktail your prefer onto the bare 2024. NONE of it will show on the top surface.

greylingr said:

alpinelakespilot2000:
I have one since I bought the Cleavelad RV toolkit, but on which edges do I use it on the scarf joint? Typically where else do you use it?

Click to expand...

Rudi-

I used the edge former AFTER the scarf joing on:
1. the leading edge of all top main skins.
2. The inboard edge of the outboard main skin
3. the outboard edge of the inboard main skin (while it doesn't seem necessary to do this since it is underneath the outboard skin, I think that you want ot make sure that the inboard edge of lower skin does not curl up at all after riveting because that would make the top overlapping skin sit a LITTLE proud.
4. I also edge formed my tank skin and leading edge skins where they meet the main skins on one wing. Doing so left that wing with a LITTLE smoother joint, especially in between the rivets and screws. If you choose to do this, though, you need to do it before dimpling the skins, I think.

In reality, it doesn't make a LOT of difference, just a subtle but noticeable difference, so don't lose sleep over it either.

BTW, I would NEVER have tried to edge roll all of this stuff with the Avery roller, it would be easy to make a mess of it.

I would ditto the previous post that indicated the NEED to do the aileron and flap nose skins. They look very nice edge rolled.

Good luck.

NO scarf???

Guys--

I clecoed my top skins on today, in order to plan the scarf joint. With the LE on and the tank installed, the skins met up pretty darn well--I'd say 1/64th" or less. I can hardly nick it with a finger nail.

Anyway, I was wondering if anyone else has skipped the scarf altogether, or if I've got something mis-aligned or screwed up? Am I setting up a mistake down the line or did I just get lucky?

Any insight appreciated!

Joe

Hey Joe,

I've only done this twice, four times if you count the bottom skins, so take it with a grain of salt.

I did scarf the skins, and I felt like the transition of the top (outboard) skin from spar to over the inboard skin became more pronounced after riveting. I think this is because the last few clecos don't have the pulling power to pull the skin really tight to the spar allowing the outboard skin to more gradually transition over the inboard skin.

Mine came out very well, but in the end I think it could have been a little better had I scarfed the skins a touch more (especially the edge of inboard skin). After riveting, I smoothed it out a touch further by using a scotchbrite roloc disc in my die-grinder to feather/bevel the edge a tiny bit more.

I know this may not make a lot of sense, but it is what I experienced. YMMV.

Good luck!

Has anyone bothered scarfing the bottom skins in this same location?
I didn't see any mention of it in the plans.

It's not like you would really notice it under there.

Mark

i scarfed the bottom of my wing. But that was just practice for the top.

I'll add here, after being pandantic I did it, and it came out fine.
Use the recommendations given on top:

1) Scarf both corners, inside of mating top and bottom skin
2) It is not nessasary to scarf the whole lenght, since you are really only interested in making the front corner nest good for appearence following the wing profile.
3) I used a vixen file and masking tape so that only the corner is vissible.
4) Use an edge forming tool on the the front and sides, same for your tanks rear.

It will come out perfect.

Regards
Rudi

This brings up an edge-forming question. I have the cleveland edge roller, where you can dial in the grip force on the vice grip.

My question is, HOW MUCH force are people using? I have been dialing it in until the rollers are parallel and touch, then a slight bit more. This does leave a visible bend line at the edge. If i use less force so there is no visible line, then it seems there is no benefit to using the tool at all.

Curious - Jae

edge roller

Having built two RV's and working on my third and owning three different types of manufactured edge rollers..I've found that the best tool for the job is a piece of 3/4" hardwood. Something like 1 1/2 wide and long enough to hold onto. I taper the ends on the belt sander and then make on thin slit widthwise on the end. Then slide/run it down the edge bending it as much as you need to get just a "little" turn down. Doesn't leave a bend line and is easier in my opinion to use.