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Forgot to dimple for screws

P

PIN 37

Well Known Member
So I have finally put the wings on my 7. I "thought" I had everything covered. Anyway, after the usual amount of sweat and tears all the bolts were in. I climbed underneath to put the screws in the skin that connects the fuse to the wing and I have forgotten to dimple the fuse skin, dumb I know, but is there any suggestions on a fix short of taking the wings off again, which I am not going to do. I did think of using pan head screw which I will do if I have to, but knowing there are a lot of smart people here I was wondering if there is a fix? :eek:
 
Ive never tried it, but why not just put a little oil on the screw and let it dimple itself by screwing it in?
 
That is pretty thick skin down there. Maybe you could countersink it? I don't know enough about structural engineering on how much strength you lose with a countersink over a dimple so run it by Vans. In real life, you probably won't lose more than 10 knots using pan head screws there!!

My skin edge there is so dented from being banged up while building, I am going to have to take a body repair hammer and fix it up a bit. It is always something!! Good luck.
 
I haven't put my wings on yet, but I've run into similar issues elsewhere.

Have you already mounted countersunk style plate nuts on the underlying skin? If so, I'd probably vote for the lube & screw technique mentioned. If it scares you, find a piece of scrap the same thickness, & do a practice run.

You can also form a dimple in place with a female die in a bucking bar, & the male die in a set for your rivet gun. Just start with very low pressure & work your way up until you're happy with the dimple. If the nut plate is already in place, you can make a 'custom' bucking bar to go over the back side of the nut plate. Just taper the outside, too, so you don't destroy the rivets holding the nut plate.

I'd be cautious about trying to countersink a skin for a #8 screw; I don't think there'll be much left to hold the head.

Charlie
 
You've come an awful long way to mess things up now. I'd reconsider taking the wings off in order to do the job right, rather than risk messing something up that will a) look horrible, b) weaken some structure, and/or c) bug you every time you look at it because it's not as good as it could/should be.

Just my two cents. I'd take them off and do the job correctly, but I'm a perfectionist.
 
Hi Charlie, c/s nutplates are in place on the wing, however at that position on the aircraft there is very little gap between the fuse and the inboard rib, so bucking would be problematic though maybe not impossible. I agree countersinking is out of the question. I have tried the screw method on a piece of scrap .032 and it worked fine, just cant remember if that skin is 32 or 40 thou.
 
I'll try to measure for you when I go down to the hangar in the morning. Do y'all have the equivalent of Harbor Freight Tools down under? You can get 'good enough' digital calipers for less than $20 US; often much less. Old style dial are often under $10.

But I seriously doubt it will be an issue, even if they're .040.
 
I would almost never voluntarily pull the wings off unless it was REALLY necessary. The close tolerance bolts are going to be a bear to get out. I would worry more about scarring of the spar holes or doing other damage than I would about a few low profile pan head screws that no one would ever see unless they get down on their hands and knees. They're not going to slow you down.
 
Can an assistant access the back side from inside the cockpit? If so, have him hold the female dimple die, backed by the heaviest bucking bar you have. Use a low pressure rivet gun to tap the male dimple die on the outside.
 
Yes Steve, I would be worried about damaging the close tolerance bolt holes as well, I might try making a bucking bar, I do have access to some quite sophisticated machinery,and then tap from the bottom with a male die.
 
I forgot to dimple the #8 holes for the rear fuselage inspection panel screws and was unable to get my squeezer in there with the longerons installed. I cleaned the skin and then put a drop of oil over the holes, and screwed a #8 screw into the already installed nutplates, after testing on some scrap. It made very nice dimples, even after inspection with a magnifying glass. Your results may vary of course...


Chris
 
Pop Rivet Dimple dies?

Not sure of the exact location but have you looked at the pop rivet dimple dies? Just a thought...
 
Is it really the end of the world If you don't install countersunk screws there? If you really don't want to try any of the (quite good) aforementioned suggestions, you could install either pan-head or AN525 washer-head screws there and wear the 0.05MPH loss in speed. You're the only one who'll know they're not supposed to be there!
 
structural?

KRviator said:
Is it really the end of the world If you don't install countersunk screws there? If you really don't want to try any of the (quite good) aforementioned suggestions, you could install either pan-head or AN525 washer-head screws there and wear the 0.05MPH loss in speed. You're the only one who'll know they're not supposed to be there!
Click to expand...

I think I remember that interface is structural in shear, those counter sinks would add to the shear strength. I would contact Vans before committing to anything on those.
 
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rv7charlie said:
I'll try to measure for you when I go down to the hangar in the morning. Do y'all have the equivalent of Harbor Freight Tools down under? You can get 'good enough' digital calipers for less than $20 US; often much less. Old style dial are often under $10.

But I seriously doubt it will be an issue, even if they're .040.
Click to expand...

According to my Harbor Freight calipers, the fuselage belly skin is .025" & the wing bottom skin is .032".

If you're building a show plane, the Cleveland die would help make a perfectly edged dimple. But you should be able to come pretty close with just a screw.

For something 'in between' in quality and a lot quicker to get, you could drill & dimple a 1" disc of .040", & use that as your die under the head of the screw. Just whack the daylights out of it in your C-frame to be sure you get a good sharp edged dimple on the homemade 'die'.

Charlie
 
I can't wait to make it these mistakes. It's only the ability to reason that wears so thin. There something to be said for doing something the second time...or third. I read these mistakes and it makes me laugh cause I know there is a day or 50 when vans universe is laughing at me.
 
IMO, it's really easy to forget to dimple those belly skin holes. I recall the call-out on the drawings to be very subtle ... almost an afterthought. I only caught the requirement by a) fervently following this site and b)looking at as many other builders websites as I could.
(Aside: I never thought I'd see the day when VAF would discuss in detail the "lube and screw" method. :D)
 
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