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countersinking wing spars

Trevor778

Well Known Member
Hi all. Im just countersinking the #8 screw holes for the tank on my 7. Im following the instructions as per vans recommendations of using a #30 counter sink as the pilot, Im countersinking to an outside diameter of .370 but it appears as though the hole is being enlarged and leaving a sharp edge at the bottom of the countersink. Ive looked at the builders sites and searched the force but didn't find the exact answer Im looking for. The countersinks come out looking very clean and the bit is not hunting but it seems as though to get the .365-.375 you need to go deeper than the .063 spar. is this true?

Thanks Trevor
 
backing bar

I used a backing bar clecoed to the wingspar. First clamp the bar to the inside of the spar flange, then drill through the holes. Then cleco through the holes. Now the backing bar will keep the pilot on the countersink from wandering.
 
Terrye's right

Terrye is exactly right. I made a little guide out of brass flat bar (1/8" x 1/2") from the hardware store. I used clecoes and/or cleco clamps to hold it in place underneath after the main hole is centered. This keeps the countersink centered and eliminates the chatter marks seen in some holes. Yes, it's a little tedious, but the end result is worth it.
 
Ummm. If the directions are like with the -10 spars, that is not correct. First you install the nut-plates for the screws and then countersink into the nutplates. A K1000-8 will take a #30 pilot and a K1000-6 will take a #40 pilot. The nutplates will keep the countersink centered and the material above the nutplate will have the opening enlarged but that is no problem as the dimpled material that sits above that will have the correct hole diameter and will align the part until it is snugged into the countersink, which then locks it in position. When I first saw that, I thought OMG but it works. Following is a picture of the countersinking in progress; the holes at the left are countersunk and the ones on the right are next. Nutplates are already in place.

FP28052011A000IH.jpg
 
I have to agree with Flion, I did my 7 spars the same way... but if I had to do it over I would not prime just yet as when you get the skins fitted and take them back off you have to countersink all those little itsy bitsy holes to accept the flush dimples of the skin.

So just prime it later before you assembly every thing permanently.

Smilin' Jack
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Whatever Floats Your Boat

Hey, there's more than one way to skin a cat...but no matter how you do it, that cat's gonna make an awful noise.:rolleyes: When I did my spars about a hundred years ago, I hadn't heard of using the nutplate as a guide for the countersink pilot. If that works well, go for it.
 
Following the directions on this one makes the work pretty quick. I did prime all countersunk holes immediately after drilling them with some rattle can primer into the lid and a cotton swab. Won't take anything to go back and hit the newly countersunk holes for the skins later in the wing build.
 
Yes, that method works too, I've found you end up with a smooth and cleaner countersink with less chatter using a drilled metal template and I can also get the deed done in half the time. The countersink and screw hole seems to come out more uniform. :)




Ummm. If the directions are like with the -10 spars, that is not correct. First you install the nut-plates for the screws and then countersink into the nutplates. A K1000-8 will take a #30 pilot and a K1000-6 will take a #40 pilot. The nutplates will keep the countersink centered and the material above the nutplate will have the opening enlarged but that is no problem as the dimpled material that sits above that will have the correct hole diameter and will align the part until it is snugged into the countersink, which then locks it in position. When I first saw that, I thought OMG but it works. Following is a picture of the countersinking in progress; the holes at the left are countersunk and the ones on the right are next. Nutplates are already in place.

FP28052011A000IH.jpg
 
I ended up using the method as suggested by vans using the nut plate as the guide. This worked extremely well and would suggest it to those in the future. My main concern though was the fact that the enlarged hole was creating a knife edge which goes against everything I know about countersinking. But I guess it is what it is now. Thanks for all the replys everone.
 
Somehow, turning a pilot at high speed in a threaded hole scares me of damaging the nutplate threads.
I opted for the extra plate behind the spar flange and they also came out great.
The principle is the same, I guess it's just a little more work to clamp and reclamp the plate from hole to hole.
 
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