countersinking the main wing spars

[kritsher]

Hi all,
I'm starting work on my wing kit (7) and I'm getting ready to countersink for the #8 screws that hold the fuel tank on. Before I bite the bullet and start drilling these expensive parts, my question is: it appears that the holes for the nutplates aren't big enough to accept a #8 screw. Do I need to drill them out? or do they get opened up when I countersink? there's no mention of drilling them out in the instructions or on any of the other website/logs I've looked at. I'm getting ready to drill them out, but can someone who has done this confirm that this is the right idea. Also, is a #21 drill the right size to drill out for the #8 screw.
thanks!

 

[aeronut67]

countersink main spar

I drilled and countersunk the rivet holes for the nut plates using the nut plate as a guide first then countersunk for the tank skin dimple. that should open the hole up plenty for the screw diameter. If you had to drill it larger ( and you shouldn't have to for countersunk screws) the nut plate has already been set in the proper place. Good luck.

 

[Paul Thomas]

21 or 27, but I can't recall now. I opened up the holes and used the #8 countersink.

I used some scrap and experimented. I used a dimpled piece al AL that represented the tank and I tested, using piece of angle stock to represent the spar, different methods. I ended up using a piece of steel under the spar to keep the head of the countersink from hunting. It came out great.

A wise builder to me to experiment with scrap before doing things on the airplane; that's the best advice I've received and I wish I'd remember to use it more often.

 

[mcencula]

Countersinking

Be sure to use a single flute countersink. I used a three flute and one of my holes ended up looking like this

Also, here is a handy little table I made up for common sizes. Hope you find it useful:

 

[Flying Scotsman]

Get the Cleaveland Tools catalog and pull out the chart they provide...I have several of them pinned to the walls of the shop, and I'm always checking and double-checking drill sizes for bolts and screws. Here's an on-line chart courtesy of Dan Checkoway, too...

http://www.rvproject.com/drillsize/

The single hole countersink bits make a beautiful countersink, but be careful...they're "aggressive" and you can easily countersink too deeply (I found this to be more likely to happen on flange "ends", the last hole on a flange where there was inadequate support for the microstop countersink cage). Also, make certain you clear the hole after *each* counterskink, or you run the risk of a sliver of metal making a nice circular gouge around your neat countersink, necessitating clean-up/alodine/etc. That said, I use them just about everywhere....

 

[rv8_builder]

Hi all,
I'm starting work on my wing kit (7) and I'm getting ready to countersink for the #8 screws that hold the fuel tank on. Before I bite the bullet and start drilling these expensive parts, my question is: it appears that the holes for the nutplates aren't big enough to accept a #8 screw. Do I need to drill them out? or do they get opened up when I countersink? there's no mention of drilling them out in the instructions or on any of the other website/logs I've looked at. I'm getting ready to drill them out, but can someone who has done this confirm that this is the right idea. Also, is a #21 drill the right size to drill out for the #8 screw.
thanks!

Have a look at this thread.

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

We followed the same procedure as Rudi with great results.

 

[Rick6a]

....I'm getting ready to countersink for the #8 screws that hold the fuel tank on. Before I bite the bullet and start drilling these expensive parts, my question is: it appears that the holes for the nutplates aren't big enough to accept a #8 screw.......

I found that simply following Van's written instructions on how to machine countersink for #8 screws produced perfectly acceptable results.

 

[AMURRAY]

Dimple

I bought a tool from Avery a while back that is made specifically to dimple the spar web. It is a #8 screw dimple die with a K1100 nut plate for the female die. The tool kit came with the male die, a couple of Allen head screws, an Allen wrench and a few k1100 nut plates. The tool is used on the inboard end of the spar were a normal dimple die will not fit.

 

[Paul Thomas]

Do you have pictures of the results? I have the #8 dimples but didn't use them because the instructions specifically warn against dimpling. Countersinking is quick and easy but dimpling is quicker and easier...

 

[AMURRAY]

Do you have pictures of the results? I have the #8 dimples but didn't use them because the instructions specifically warn against dimpling. Countersinking is quick and easy but dimpling is quicker and easier...

I do not have pictures. At least not one close up. The tanks are on the wings now. From what I remember the dimples look like any other dimple. The spar web is .040 on the RV6. Maybe different on the RV7-8 wing. Also my spar is not anodized. I don't recall the builders manual saying anything about dimpling. Countersinking a hole for a #8 screw in .040 is going to open up the hole a lot larger than a #19 drill bit. I guess it was just personal preference. I believe I riveted the K1100 nut plate to the web and then used the screw dimple die.

 

[Flying Scotsman]

...The spar web is .040 on the RV6. Maybe different on the RV7-8 wing. ...I don't recall the builders manual saying anything about dimpling. ...

The -7 wing spar is .063, and the instructions *specifically* say:

Machine countersink (trying to dimple the 0.063 thic spar flange will result in severe distortion) the platenut attach holes in the W-706A spar flange.

Not to criticize, but you should have mentioned that you dimpled the spar for a different model, with possibly different thickness spar flange, in your first post (this is *RV-7/7A* forum). Someone could have taken your advice on their (much thicker) spar and ruined a very expensive part.

 

[larrynew]

Followed Van's instructions

Just another data point about countersinking the spar for the #8 screws that hold the tanks on. I followed Van's instructions about first riveting the platenut on and then using a #30 piloted countersink. Worked great. Even used a three fluted countersink in my Sioux air drill. The more I build, the more I'll have to have a compelling reason to deviate from Van's plans.