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What would you do? countersink vs dimple

Coaltowngarage

Active Member
ok, so the kit I bought had the tailfeathers mostly complete and the wings about 75% done. The top wing skins and the tailfeather skins were all countersunk rivets. The surfaces are flawless. I'm at the point now to begin preparing the fuse skins for riveting. If it were you, would you complete the airplane countersinking rivets to match the previous work or dimple? I was told the plane is a show winner if the workmanship is completed as well as the wings and tail had been done. Is the difference something that will be very noticeable on the finished product?
I know this is subjective I guess, and folks will have different opinions. I want the hear them.
 
Only countersink if the skin is at least .032 thick. Thinner sheets must be dimpled, else the countersink will open the hole before achieving the necessary depth for the rivet head. Rivet size also matters, so the above rule requires modification for larger diameter rivet.
 
I'm not done yet with my 9A yet so am no expert on building planes but this question scares me. The wing and tail skins were countersunk?? Is that even airworthy? Did the kit come with instructions? The instructions tell you what to do and what thickness to start countersinks. You don't have to countersink to get flawless results. What model is this anyway?
 
Easy call - my countersinking skills aren't nearly as good as my dimpling skills. I'd probably end up buying new skins several times over...
 
I wonder if you are referring to the builder dimpling the skin, then lightly countersinking for a better rivet fit? IMO, not needed. What might be needed are better dimple dies.
 
Dimple

I think you need to provide more information and some photos because the skins should not be countersinked. Maybe you mean flush riveted? You're scaring us!:D
The manual is very specific about what is dimpled vs countersinked.
The fuse skins are dimpled.
 
Its an early 6, the skins are riveted with flush rivets and the holes are countersunk. The plans say that countersinking is acceptable on panels .032 or over. Ive read of a few others doing it this way. When I say flawless. I mean glass smooth, absolutely zero deformation around any rivet, the tank skins and bottom skins are dimpled. This isn't a question of airworthiness, its a question of aesthetics, would it bother you if the rivets on the top of the wings looked different that on the fuselage?
 
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Countersinked

Bother? Nope. Only that it was buillt in compliance with 43.13 and it's safe.
Maybe a 6 builder will comment. Seems odd to contersink .032 but I'm no Engineer and mine is a 7A.
I do know it is totally possible to dimple a skin perfectly. I've seen many an airplane with perfect dimpled skins.
If it's not an airworthiness question then as they say, it's your bird.
I would ask Vans.
 
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Guys, you can countersink .032 for -3 rivets. Even Vans says so in section 5.

If you do the math, you'll see that .032 is the absolute thinnest sheet that you can get away with countersinking without enlarging the hole. a perfectly countersunk hole will leave a -3 rivet a couple of thousandths proud.

Having said that, If you ever botch one to a point that you have to go up to a -4, you're screwed, because then you absolutely don't have enough material thickness to countersink for a -4. For that reason, I would dimple the fuselage if it were me. But then again, I'm not building a show plane.
 
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Comments

I'm a -6A builder and for me safety comes first, performance second and aesthetics is third.
I prefer to dimple wherever possible and only countersink if I cannot dimple e.g. .040 is difficult to dimple well.
The best dimple dies for a smooth finish came from Avery but I'm not sure if they are available any more after Avery retired.
It's obviously also equally important to be able to set rivets for a good finish and some builders make the effort to back rivet wherever possible.

On a -6 the wing top skins are mainly .025, apart from the area behind the tanks (.032), so should be dimpled and not countersunk. It is possible though that the previous builder might have put on non-standard thicker skins for countersinking.

The fuselage skins are generally .025, so must be dimpled and not countersunk.
 
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I do not enjoy countersinking. I couldn't imagine doing all the holes that way. It took long enough to banging on the c frame with a hammer thousands of times.
 
Countersinking .032 is right on the edge. The mil standards for riveting specify .040 as thinnest material for machine countersinking 3/32 rivets. I built a -6 and while the plans call for machine countersinking .032, it is only a couple of thousands from knife edge. Any side load on the pilot will egg shape the hole. I highly recommend dimpling .032. If you want to improve the aesthetics a very light hit of the dimple with a countersink will clean up the appearance.
 
The common to all models Section 5 in the construction manuals give specific recommendations regarding dimple countersinking vs machine countersinking.

In a nut shell...... machine countersinking .032 is allowed in situations where it might be necessary but it is recommended that all thicknesses up to and including .040 be dimple countersunk. Machine countersinking anything thinner than .032 is never allowed. (This is relevant to 3/32 rivets)
 
Im just going from memory here, but arent the outboard wing skins 0.025? Were those countersunk as well?

Overall thr dimpled joints are quite a bit stronger in sheer, so it sounds like he made a pretty, but weaker wing.
 
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If the empennage and wings were truly countersunk, and not dimpled, I would say he?s got nice wall art, maybe a bar table.. but he probably shouldn?t continue and make a flying plane out of these parts. Like someone said earlier, dimpled joints are stronger in shear than non-dimpled, and Van?s doesn?t approve of countersinking these thinner skins..
 
I try to stay out of these; but, an important point is missing. Drawings override 43.13, specifications, references, standard shop practice, whatever. Is there a detail showing which method to use? If so, the associated engineering analysis is (assumed) complete and is the proper application. There?s places in drawings I?ve seen which would seem at odds with various design standards; example, where the 032 tank skin and 040 tank flange are double countersunk on RV 4s. The associated screw head height is 072.

Another point. Rocket wing drawings I?ve seen replace the top skins with one piece 032 and specifically calls for CS. I?m guessing less an added strength issue than it eliminates a lot of steps versus dimpling flanges, ribs, and skins.

Anyway, drawings supersede everything else.
 
My SOP

My Standard Operating Procedure is to only countersink what I cannot dimple.

For -3 rivets, typically anything greater than 0.040" will get countersunk.
 
.032 skin - inboard wing and stabilizers
.025 skin - outboard wing, flap, and possibly rudder and elevators
.016 skin - ailerons and possibly rudder and elevators
In the face of Van's recommendation (section 5E in the plans) to dimple in metal .040 and thinner, I would not be comfortable with even the .032 skins being countersunk and if the other skins were also countersunk then the kit should be considered unusable. It was not clear from the OP what surfaces were countersunk. Were the outboard wing skins or the control surfaces countersunk? Also, going forward, the fuselage skins less than .040 should be dimpled, not countersunk.
 
Curious to know if it was the seller that told him it will be a showplane if the rest of the skins are countersunk. My skins are all dimpled and look amazing. It's actually hard to screw up dimpling if you've done some research, studying, and practice before doing the real parts.
 
Years ago I had a RV-6 come in for inspection and noticed the horiz stab rear spar rivets were all loose/smoking, they had all been countersunk. Probably was good looking when it was built, but not built right. Only solution I could think of short of total disassemble was to double up the rivets at the spar by drilling in between every existing rivet hole, remove the spar & prep the new holes properly with dimples and re-rivet it all back together. Not the prettiest fix but at least it was structurally sound.
Would be much better to have (& fly) a properly built plane than a pretty plane you were worried to fly.
 
Curious to know if it was the seller that told him it will be a showplane if the rest of the skins are countersunk. My skins are all dimpled and look amazing. It's actually hard to screw up dimpling if you've done some research, studying, and practice before doing the real parts.

The best investment you can make in tools is a top quality set of spring-back dimple dies.
 
One thing to also consider.

If you are using a DRDT2 dimpler, make sure you set up the handle and sets correctly. When you look at the action, the most force occurs when the assembly is towards its lowest - that means the adjustable set holder on the top part needs to be wound in, which leaves the handle well down on stroke. If you have the set holder wound out, when you bring the handle down, the mechanical advantage isn't as good.

You won't notice this on thin skins, but we have just noticed it on the .032 skins on the RV10. The rivet dimples just didn't look crisp and we are using Cleaveland spring back dies. Once adjusted, all was fine and we got a great crisp dimple - and RSI/tennis elbow :eek::D

Same can happen with a pneumatic riveter when setting long rivets - the action is based on a cam and if the cam is not at it's correct point, you don't get full squeeze. That is easily solved with a Numatx riveter :p
 
I prefer dimple on 0.032 because with 3/32 flush rivet it is knife edged. In the certified aircraft world it is usually a no no to have more than 67% countersking to skin thickness. Up to you! It should be OK, but not quite as strong as dimples.
 
When I built my first 2 RV-6s, I countersunk the rivets on the .032" empennage skins. To this day, 27 years later, they still look great and no smoking rivets.

Would I do the same thing again? Absolutely NOT. It was painstaking to make sure there were no enlarged holes and they are certainly not as strong as if they were dimpled.
 
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