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Wing Spar Tank Nutplate Countersinks

J

jcoloccia

Well Known Member
I'm just starting on my wings, I've drilled exactly one hole and I already have a question. So how deep are you guys making the #8 tank attach countersinks in the spar? I have a test piece with a #8 dimple in it, and it still doesn't fit flush in the spar countersink, yet I've already chewed through to the otherside with the countersink bit. Is this normal, or am I doing something really wrong? I only did one, saw it going funny and stopped so I'm thinking I can safely ignore one overly countersunk hole as long as the rest of them are proper (and the one I did isn't that bad, anyway).

edit: I found a couple of threads on this, but there didn't seem to be any real consensus what the proper way is.
 
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How I did mine...

According to what I have read, the measurement for the hole after it is countersunk should be:

...We countersink until the top of the screw is level with the surface, then go 2 clicks deeper on the microstop. The actual outside diameter of the countersink measures .365 to .375"
Click to expand...

Look at this thread for additional info:

http://www.vansairforce.com/community/showthread.php?t=2740&highlight=countersink+spar+rvator

Hope this helps.

-John
Houston, TX
RV-7A Wings
 
compren said:
According to what I have read, the measurement for the hole after it is countersunk should be:



Look at this thread for additional info:

http://www.vansairforce.com/community/showthread.php?t=2740&highlight=countersink+spar+rvator

Hope this helps.

-John
Houston, TX
RV-7A Wings
Click to expand...

Exactly my point...this doesn't jive with any of my measurements. Currently, I'm at .360, and that's already WAY deeper than 2 clicks, 5 clicks or even 10 clicks beyond flush, and the countersink's through to the other side. Just to anchor this in reality, when I mic'd the head of a AN509-8R8 screw, it measures almost exactly .3 (the particular one I picked measured .295, actually).

Now it makes sense that it should be roughly .07 wider than the screw head since that takes into account approximately the skin thickness X 2 (it'd be 1X if we were talking about the radius instead of the diameter), but .07 is huge. MUCH larger than 2 clicks.

I'm thinking, though, that the 2 clicks business is BS and that we're intended to just go ahead and countersink right through the spar. This is the only reason I can figure that those are countersunk nutplates instead of the more "appropriate" non-countersunk. The #6 nutplates for the inspection plates are non-countersunk...I'm presuming this is because the #6 dimple is much smaller and the resulting countersink doesn't penetrate the spar.

I dunno...I did have a beer before I made the measurements, so maybe I'm just looking at this cross-eyed, or something. :D

Either way, I still can't get over how cool those spars look...it's a shame they're just going to get covered up.
 
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Wing Spar Countersinks

Hi John

I remember going through the exact freakout about three months ago. You are, after all, making holes in that really nicely anodized spar. Do read the thread. I found that taking a 1" by 1/8 thick piece of bar, drilling it so that you can cleco it to the nutplate rivet holes underneath the spar flange and then using a slow electric screwdriver will give you really nice, smooth holes. I used a caliper as per above to measure the diameter. Worked great.

Regards,

Michael Wynn
RV 8 Wings (tanks)
 
Countersink the spar

Just to echo the others on this, I remember using the .365 measure & they came out fine, also when I did the 2nd set I had rivetted the nut plates in & these worked better as the nutplate acts as a guide & keeps the countersink centered. also a slightly slower speed stops chatter & producers cleaner cuts

Stephen
N570Z (Reserved)
RV7 Tipping the canoe
 
mlwynn said:
Hi John

I remember going through the exact freakout about three months ago. You are, after all, making holes in that really nicely anodized spar. Do read the thread. I found that taking a 1" by 1/8 thick piece of bar, drilling it so that you can cleco it to the nutplate rivet holes underneath the spar flange and then using a slow electric screwdriver will give you really nice, smooth holes. I used a caliper as per above to measure the diameter. Worked great.

Regards,

Michael Wynn
RV 8 Wings (tanks)
Click to expand...

Actually, that's exactly how I'm doing it (except for the screwdriver thing). I stole the idea from Dan's site (of course) :), but I modified it a bit to end up with a precisely located #30 hole in the plate to match the #30 pilot.

I first drilled the diagnol nutplate rivet pattern into the jig using the spar as a guide, removed the jig and clecoed a K1000-8 (non-countersunk) nutplate to it (who's screw hole is, incidentally, darn near the same size as a #30 drill). Then I used my drill press to drill a #30 hole right through the center of the nutplate using the nutplate's screw hole as a guide. Then I clecoed the nutplate through the center hole, lined up the wings to be more or less level and then drilled through the nutplate wings to locate the rivet holes for the non-diagonal nutplates. This leaves me with a jig I can use for the diagonal and non-diagonal nutplates with a perfectly centered #30 hole for the coutnersink pilot to ride in. Then I proceeded using Dan's technique of cleco/clamp/countersink. Proceeded is too strong of a word, actually, since I only did one, but it really is WAY faster than it sounds.
 
I used a modification of "Dan's method". My 3 hole jig was made of steel so the #30 pilot bore would not wear out fast like one in aluminum would. I countersank all the rivet holes in the spar first and then came back through with the jig plate, 2 loose rivets and 2 alligator clecos. The 2 rivets keep the jig aligned and are not in the way of the microstop cage. The cage keeps the rivets pushed in place. The alligator clecos are clamped out of the way of the microstop. I was happy with the method.

FYI, I think the "guideline" about "2 clicks" on the microstop for substructure countersinks is complete bilgewater. For whatever assembly that needs it, I dimple the surface piece and then measure the backside of the dimple with a graduated loupe. (magnifying glass with a measuring scale). C'sink to the right top diameter on the substructure and move on. 2 clicks?....bah! :D
 
jcoloccia said:
I'm just starting on my wings, I've drilled exactly one hole and I already have a question. So how deep are you guys making the #8 tank attach countersinks in the spar? I have a test piece with a #8 dimple in it, and it still doesn't fit flush in the spar countersink, yet I've already chewed through to the otherside with the countersink bit. Is this normal, or am I doing something really wrong? I only did one, saw it going funny and stopped so I'm thinking I can safely ignore one overly countersunk hole as long as the rest of them are proper (and the one I did isn't that bad, anyway).

edit: I found a couple of threads on this, but there didn't seem to be any real consensus what the proper way is.
Click to expand...

What John said above was exactly what I was going to type. Man, this board is good, answers to questions before I even ask them. :eek:
 
jcoloccia said:
Exactly my point...this doesn't jive with any of my measurements. Currently, I'm at .360, and that's already WAY deeper than 2 clicks, 5 clicks or even 10 clicks beyond flush, and the countersink's through to the other side. Just to anchor this in reality, when I mic'd the head of a AN509-8R8 screw, it measures almost exactly .3 (the particular one I picked measured .295, actually).
I'm thinking, though, that the 2 clicks business is BS and that we're intended to just go ahead and countersink right through the spar.
QUOTE]



OK, I read this thread and the one mentioned above and I haven't heard anyone mention what the ID of the hole (not C-sink) should be.

I have #30 and #21 c-sink bits and the 21 seems to make a cleaner/chatter free c-sink than the 30. I thought using the #30 cutter was supposed to prevent breaking all the way though the spar flange, thus enlarging the #21 hole but they both seem to cut the hole oversize by about the same. HELP!

One other comment: Vans recommends using a #30 c-sink cutter with a nutplate as the guide. Is it because there is something magical about the #30 cutter or strictly because it fits the nutplate well?
Click to expand...
 
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Do not try to make the test dimple fit flush! You will make the countersink too deep! The screw with nicely nest the dimple down into the countersink farther than you are able to push the test piece with your fingers. Thus, either follow Van's flush + 2 clicks or the .365-.375 (?-memory) measurement with a caliper. Doing the latter I found that flush + about 6-7 clicks was about right and left me right in the middle of the range Van's recommneded in RVator.

The #30 countersink is recommended because it fits the #8 platenut well. They're all 100 degrees so it really doesn't matter what size you use.

Good luck.
 
alpinelakespilot2000 said:
They're all 100 degrees so it really doesn't matter what size you use.
Click to expand...

Exactly. You can use a #21 or #30 or any size pilot but the cutters are 100 degrees so assuming you c'sink to the same depth the inside diameter (or the diameter at the bottom) will be the same. It is slightly larger than the original hole - IOW, there is some material removed on the "bottom" of the flange.

Thomas
-8 wings
 
I also did what M Wynn did in that I took a piece of scrap about 1/8" thick and 6 to 8 inches long. I drilled 3 #40 holes to match the nut plate holes (several sets to match multiple locations at one time). I would center this on the nutplate screw hole and cleco inplace (to ensure alignment with nutplate holes) then clamp it. Remove the clecos and then machine counter sink with a #40 pilot using a micro stop. The scrap piece with the csk pilot centered in the center hole acts as a guide (in lieu of the nutplate per the assy manual) and produces great countersinks without the chattering and ragged edges.
 
A different jig...

I drilled some 1/8" scrap with the hole patern and used two -3 rivets sandwiched between it and some .025 scrap as guide pins. The 1/8" scrap ends up with a slight countersink, but the bottom of the hole is still straight so it guided the cutter nicely. The nice thing about this is that I could move it very quickly without messing with any clecos and the alignment was always perfect. On the downside, I built it in a way that prohibited me from using it on the angled nutplates.

051015_002.jpg


Here it is spring-clamped into place. The -3 rivets are short enough that they do not interfere with the countersink cutter.
051015_003.jpg
 
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RV7Factory said:
I drilled some 1/8" scrap with the hole patern and used two -3 rivets sandwiched between it and some .025 scrap as guide pins. The 1/8" scrap ends up with a slight countersink, but the bottom of the hole is still straight so it guided the cutter nicely. The nice thing about this is that I could move it very quickly without messing with any clecos and the alignment was always perfect. On the downside, I built it in a way that prohibited me from using it on the angled nutplates.
Click to expand...

Brad gets the prize for the "Clever Solution of the Month". Very slick.
 
Brad's trick worked great for me. I was able to grind the end down to do the angled nutplates too. I waited until all the straight ones were done, just in case. The end result was a pointy version of Brad's pic, with the first "pin" at the apex of the point. I didn't even use clamps to hold in in place...if you make the handle part long enough, you can hold it in place with your free hand and move it quickly from hole to hole.

Joe
 
william weesner said:
doesnt this end up the same as a nut plate after you do the first one?
Click to expand...
I guess it does somewhat, but the coutersinking of the bar stock is so shallow that any chatter is quickly removed when the cutter enlarges the hole, and by that time the pilot is into the straight part of the guide hole.

Thanks for the kudos guys! :)
 
I don't think a longer pilot would help ... unless you had a really thick piece of stock underneath as a backer.
I did all mine with the Van's method of riveting the nutplates on and they turned out great. This was WAY faster than moving a piece of Al angle after each set of holes. I had no problems at all with this technique.

Thomas
-8 wings
 
It seems like everyone wants to make this harder than it needs to be. If you follow Van's instructions, and use the nutplate to guide the countersink, everything comes out perfect. I suspect the problem is that everyone is using their air powered drill, which will chew metal and wobble in no time at all. I used a portable electric drill, which goes slow and worked great. Slow, steady pressure will get this done soon enough, without having to build some sort of fixture.

I've seen this debated over-and-over, and everyone wants to build a fixture that fixes their problems. That's fine, if you want to spend the time, but I can assure you that Van's method works just fine. Just be careful, and do not rush this.

BTW, I understand the concern about cutting into that wing. I had the same apprehension. I delayed working on the wings for two weeks after I got them inventoried before I drilled the first hole. Once that first hole is drilled, things go a whole lot better.

Also, I did not measure the holes with a caliper. I simply drilled a hole in a piece of scrap, dimpled it, and used is as a test gauge to tell when the holes were done. As far as not being able to push the test strip into the hole far enough with your fingers, you should not have to push. If the test strip does not fit the hole correctly, then you are using the wrong countersink bit. I do have a few countersink bits that are a different angle that what we use. I think we need 100 degree bits, and I have a few 120 degree bits, but I could have this backwards--read chapter 5 of Van's manual if you have any doubts.

Cheers,
Tracy.
 
thallock said:
As far as not being able to push the test strip into the hole far enough with your fingers, you should not have to push. If the test strip does not fit the hole correctly, then you are using the wrong countersink bit. .
Click to expand...

I might have exaggerated the "push" a little bit in my earlier post. Overall, what I was primarily referring to was the RVator article in which Van's recommended NOT using the dimpled-test piece method for the wing spars because, in their experience, many people who did this were drilling their countersinks too deep trying to get the dimple to sit flush. Likewise, when I used the test piece on the first hole I found that I too got up to Van's recommended countersink size well before the test dimple fit perfectly flush. However, by the time the tank was screwed onto the spar, the screw nested nice and flush into the dimples and countersinks, even if the countersinks had seemed a little bit undersized initially.

I agree with you that this is all probably being over-thought and that Van's method (w/ the platenut as guide) works just fine, especially with a low-speed, high-torque cordless drill, but definitely do not countersink too far. If you do, Van's indicated a recommended fix, but it appeared to be a painfully laborious process.
 
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The ONLY reason I didn't use Van's method is that the hole on the bottom of the flange becomes nesceserily knife edged and a little rough due to the depth of the cut. With the nutplates in the way, it's very difficult to debur the backside of the hole. It's probably not nescessary, and on my next plane I will likely just do it just like Vans says to do it.

just my totally inexperienced $.02 and I'll change my mind 5 more times when and if I ever build another RV.
 
William-

You're probably right, if the pilot was longer it would engage the nutplate earlier and eliminate chatter.
Dunno if it would be more prone to breaking, though.

Anybody wanna make one?? :)

Thomas
-8 wings
 
So I drilled my first hole in the spar. I'm pretty close to 0.370" in diamter at the top of the countersink. This results in the bottom of the hole being somewhere between 0.21" and 0.22" in diameter, which is significantly larger than the #8 screw diameter of .164". Is this right?

10019174yf.jpg
 
Wing spar countersinking

I had good results with Van's nutplate method and cordless drill. Push hard, no lube, no chattter.

John
 
MTBehnke said:
Is everyone match-drilling the tank skins to the spar before countersinking the spar for the #8 screws?
Click to expand...
I haven't seen or heard of anybody doing this. Because you are using screws/nutplates, I am not sure this would provide much benefit.
 
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