K

kleindoc

Member
Starting on my wing kit.

Why am I machine countersinking my nice new spars for #8 screws (for the tank skin plate-nuts) when the screws in bag # 1924 are pan-head screws?

Are the screw tops supposed to be flush with the tank skin? There will be a gap between the dimple in the tank skin and the underside of the rim of the pan-head.
 
Tank skin to Spar

It seems you are looking at the wrong screws, the tank skin to spar uses a c/sink screw. Also when you do this drill out the centre hole, fit the nut plates then countersink. The np will stop the c/sink from chattering.

hth Stephen
N57OZ RV7 Finish
 
Funny you ask about this. I wasn't too crazy about that step either. It's probably one of the few areas I thought could have been done a little different...but...you have to work with what you have.

Those screws are #8 c-sunk's. They're hard to miss because you'l have about a pound of em in a bag somewhere. As you countersink the spar you'll find that the C-Sink doesn't exactly stay tru to the hole. The holes get bigger and bigger as you go. Be careful and keep the c-sink going straight and smooth. If it starts to chatter, slow down and investigate. Always check your depth by comparing the screw and the dimpled skin. Take a look...

http://www.experimentalrv7.com/Systems/Wing/PC260014.JPG

http://www.experimentalrv7.com/Systems/Wing/PB200033.JPG

You can take a ball rotary file to assist in the removal of the shoulder where your dimple MAY REST IF IT'S NOT QUITE ENOUGH. The ball may not be the normal 100 deg of the countersink but it's okay for removing a little from the area where the skin will sit.

Finish the hole off by drilling it to the size needed to give you between .025 - .032 metal to prevent crack propogation at the bottom of the countersink. Polish it if you want. I did. Why this..you may ask. If you look at the hole when your done, you'll see that the bottom of the countersink is paper thin. Multiply that times thenumber of screws..and well, I didn't like the odds of a crack starting on my new spars.

This is not a standard thing to do to a hole. Whatever the case, there should always be enough thickness for the countersink. I wouldn't be alarmed at all. There's thousands out there flying without a problem It's guys like me that might notice. Thats all.

Good luck.

John
 
This might help get nice straight countersinks without wallowing out the hole. Put the caged countersink in a cordless drill and run it on the slow speed. Make several short bursts to cut the countersink and you may have better results. I was having trouble when using an air drill and switched to the cordless and it solved the problem. The same procedure worked great on the trailing edge wedges also. I hope this helps.
 
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Van's method stinks

I'd suggest you try one or two holes the way Van's suggests it. you'll quickly see using the nutplate as a guide for the countersink doesn't work worth a darn. For one the pilot is a tad loose in the threads which allows chatter. Two the countersink has to be soo deep it will penitrate the spar a bit. This opens the hole up more making the chatter worse. Also with the nutplate riveted in place you can't deburr the backside of the hole you just enlarged.

Insted back up the hole with a piece of predrilled scrap aluminum about 1/8" thick. cleco and clamp this behind the spar and countersink into it. It will act as the proper guide for the pilot allowing for chater free perfect countersunk holes. It's time consuming, however it's worth it if you ask me.
 
Thanks to all who responded. I was looking at the wrong screws as N57OZ suggested.

This problem will be eliminated once the change in bag style is fully implemented. (The new bags list the exact content, right on the bag).

I found the #8 platenuts WITH C/S HEAD SCREWS (rather than pan -head screws) in another bag identified in the parts list as 'tank attach hardware.' It might have been nice if the parts list said that bag 1922 1 contained #8 platenuts and c/s screws.

Thanks also to Van's tech support personnel.
 
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I absolutely agree with Bruce about using a home made jig plate. Make it out of steel though, and it won't get worn by the multiple uses.

I went through and c'sank all the rivet holes first. Then came back with my fixture, two AN426AD3 rivets and a couple of clamps. Place the fixture behind the holes, insert rivets, install an alegator clamp or two (out of the way of the c'sink cage), C'sink center hole. The rivets hold the fixture alligned just in case a clamp wants to slip. The C'sink cage will hold the rivets in place.


wingtime said:
I'd suggest you try one or two holes the way Van's suggests it. you'll quickly see using the nutplate as a guide for the countersink doesn't work worth a darn. For one the pilot is a tad loose in the threads which allows chatter. Two the countersink has to be soo deep it will penitrate the spar a bit. This opens the hole up more making the chatter worse. Also with the nutplate riveted in place you can't deburr the backside of the hole you just enlarged.

Insted back up the hole with a piece of predrilled scrap aluminum about 1/8" thick. cleco and clamp this behind the spar and countersink into it. It will act as the proper guide for the pilot allowing for chater free perfect countersunk holes. It's time consuming, however it's worth it if you ask me.
Click to expand...
 
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