Countersinking wing spar.......?

[CitationXRV8]

Getting ready to countersink wing spar. I've done a lot of research and studying of plans preparing for the first steps. Vans recommends using a #30 countersink using the platenut as a guide. Some guys fabricate a countersinking tool to help guide the #30 countersink. Both great ideas and seems to work.

My question is, why not just use a #19 drill to drill out the hole and then use a #19 countersink? That would eliminate using the platenut or countersink tool. Would this be an acceptable procedure?

Thanks,
Joe

[TShort]

The depth of the center c'sink for the screw is such that there is no material left on the back side to support the pilot of the countersink. You need something back there to guide the pilot - otherwise you get horrible chatter and a buggered up hole.

I used the nutplate method with good results...

T.

[Yukon]

Van's method worked good for me (nutplate centering).

[Dustin B.]

I just did this a few weeks ago. I used some angle aluminum clecoed to the inside of the flange, and matchdrilled the angle using the spar as a guide. Then I used a countersink bit of the same size to finish it. The angle serves as a guide and keeps down the chatter. Boelube helps too. Some pics

Any more questions, just ask.

-Dustin

[Rick6a]

Originally Posted by TShort

The depth of the center c'sink for the screw is such that there is no material left on the back side to support the pilot of the countersink. You need something back there to guide the pilot - otherwise you get horrible chatter and a buggered up hole.

I used the nutplate method with good results...

T.

Builders try all manner of technique to deal with the wing spar countersinks. The quote above accurately says it all. I too found that simply following Van's suggested method produced beautiful high quality countersinks with a minimum of fuss and bother. Why try to reinvent the wheel?

[RVNineA]

I used Van's method also, seemed to work very well.

[bullojm1]

I used Van's method too. I did get some slight chatter on some holes -- maybe 30% of them. I fixed this by using a standard electric drill turning the countersinking bit slowly. Since then, this has been my defacto standard for countersinking. The low speed/high torque of the power drill keeps the countersinking bit from chattering. Another advantage to the corded drill is you can lock the speed and keep the drill going without pressing the trigger. This makes countersinking a few hundred holes a lot easier IMHO.

[Yukon]

I think all of these complex "centering" techniques arise from "builder websites". My guess is a builder misread the plans, didn't install the nutplates first, and had difficulty making the countersinks. The "fix" was documented on their builder site, and now we have all these time-consuming jigs and guides for countersinking.

Installing nutplates before countersinking is counter-intuitive, and can be overlooked, especially if you are keeping one eye on a builder website while reading Van's plans. If you simply follow Van's instructions, the nutplate does a marvelous job of centering the countersinking tool.

Test the countersink for depth on scrap metal, don't turn it too fast, and you will get perfect countersinks every time.

[jcoloccia]

Actually, the reason a lot of us use a jig isn't "builder websites". It's that the backside of the countersink is very rough once you're done with it. I wanted to go back and deburr it. Also, I didn't want metal chips to wedge between the nutplate and the spar.

Anyhow, that said I'd probably just use the nutplate method next time.

[Brantel]

I used the Van method and it worked great. Adjust the countersink till it just bottoms out the pilot in the nutplate at the last second. Use a variable speed drill and turn it slow to prevent chatter. You may get some chatter till the pilot bottoms out and then it should smooth out right at that moment.

You do not have the opportunity to debur the backside in this situation but, how do you debur a knife edge?

I don't like having 200 holes in my spars that break all the rules about countersinking to the point were you create a knife edge but that is the way Van designed it so that is what we get.