Tank Screw hole enlargement - Any secrets?

704CH · #1 11-09-2009, 10:28 AM

Hey guys, I am going to be widening the prepunched holes for the Tank Attach screws in my -7. Are there any secrets to this step? I plan on backing with a 2x4 and drilling them directly to a #19 bit, hoping the drill keeps itself exactly centered.

Does anyone see any problems with this? Is this how others have done it?

Since I have never done this, I don't want to get done and have a bunch of mis-alligned holes.. ;-)

Thanks !

Kahuna · #2 11-09-2009, 10:52 AM

Are you talking about the Z bracket holes in the web?
Oh wait, your probably talking about skin to spar flange. I dont predrill so I cant help you.
Im one of those looney bins that just dimples.
Working on mine now.

WingsOnWheels · #3 11-09-2009, 11:22 AM

I'm not sure the assembly order of the 7, but wouldn't it be best to drill those in assembly with the spar? Eliminate the possibility of misalignment.

704CH · #4 11-09-2009, 12:01 PM

Sorry if I wasn't more clear. I am talking about the holes for the 70 some screws that attach the tank skin to the spar and the leading edge attachment strip. Of course I can't drill in assembly with the spar because the nutplates are already in place on the spar flange and the holes are countersunk to accept the screw heads.

Directions indicate you enlarge the holes to a #19 bit and I just wanted to see if there was any tricks to this step. I want the tank skin to sit well with the main skin after this step..

If this doesn't clear it up I will send some photos.

Thanks again

WingsOnWheels · #5 11-09-2009, 12:15 PM

I see where you are comming from, on the 6, I drilled all the holes out to #19 in assembly before installing the nutplates. In your situation a wood block isn't a bad idea, but you can probably get away without it. However, I would step the size up rather than just jump to the #19.

Doug Rohrer · #6 11-09-2009, 01:34 PM

It sounds like you need a "Unibit" step drill. They seem to stay centered and make good round holes, but I have never seen a set for number drills, only fractions. Does anybody know if anyone makes such a thing?

claycookiemonster · #7 11-09-2009, 03:07 PM

If I remember, there really wasn't a proper sized bit for this screw. I know when I used the air drill, the high speeds caused alot of "rattling" around in the hole, however a normal rechargable household drill did much better at it's slower speed. I think this was brought up in an old issue of RVator?
Clay "CookieMonster" Cook
Paused

aparchment · #8 11-09-2009, 03:34 PM

A step unibit is probably the best option. I worked great for me.

N941WR · #9 11-09-2009, 06:12 PM

I just used a #19 drill bit, drilled them to size, debured, and dimpled them. Like the rest of the kit, they will line right up.

No need for a unibit. However, one advantage to the unibit is that it deburs at least one size. Just make sure you don't over drill them or take off to much aluminum with the next step on the bit.