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Old 07-05-2021, 08:29 PM
mburch's Avatar
mburch mburch is offline
Join Date: Feb 2005
Location: Oregon
Posts: 1,315
Default Ten-foot drill bit

I followed the factory guidance for installing plastic wiring conduits in my wing ribs. Now that I'm working on attaching the wings, I've realized that the end of the conduit is nowhere close to the prepunched wiring hole in the fuselage. Since I need to accommodate a pair of 1/4" pneumatic tubes as well as a thick bundle of wires, I was going to need to add more holes in the fuselage anyway, so I decided to use the existing hole for the pitot/AOA plumbing and create a new hole for the wiring.

After checking for edge distance and clearance issues, I decided I ought to be able to put the new hole exactly in line with the end of the conduit. But how to locate the hole accurately? The gap between the wing and fuselage is too narrow to get an angle drill into, and even marking it with a sharpie seemed problematic. Then I thought, what if the hole could be drilled starting from the other end of the wing? All you'd need is a ten-foot drill bit!

I'm sure very long drill extensions exist somewhere, or you could daisy-chain a bunch of the 18" ones together, but those ideas sounded expensive. Instead, I fired up the lathe and made something that did the job, using nothing but stuff I had laying around anyway.

I turned down a piece of aluminum rod into a bullet-shaped thing. One end has an 8-32 stud, and the other end has 1/4-28 threads into which I screwed a #40 threaded bit:

This I screwed to the end of my electrician's fish stick:

Then it was a simple matter of running the resulting contraption in from the wing tip to the root, chucking the outboard end in a drill, and having at it. It's not totally unlike snaking a drain:

Result, one pilot hole exactly centered on the wing conduit:

Sure, putting a drill bit on the end of a fiberglass rod is a dumb idea. But then again, if it's dumb but it works, maybe it's not so dumb...
Matt Burch
RV-7 (last 90%)

Any opinions expressed in this message are my own and not those of my employer.
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Old 07-05-2021, 09:24 PM
Scott Hersha Scott Hersha is offline
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,956

It’s funny that you posted this, because I did the almost same thing today. I needed to enlarge wire run holes in the wings where a previous builder had installed very small snap bushings. The Vans tech advice limits the recommended hole size in wing ribs, depending on where the hole is made:

The installed snap bushings were in the existing tooling holes. I wanted to install a thin walled PVC tube as a conduit, but couldn’t squeeze it through the allowed hole size. I ended up enlarging the existing holes after removing all those small snap bushings to 5/8”, using a 4’ drill bit extension that I cobbled together from tools purchased from Menards. I bought a 3’ extension and attached it to a 12” drill bit extension with a locking hex bit end, and used a unibit ground down to the 5/8” max diameter step since it had to go through one rib and then continue through to the next one, etc. Four feet was enough for my RV6 drilling in from each end of the wing toward the middle (wings are finished, but still on the wing stand).
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO

Last edited by Scott Hersha : 07-05-2021 at 09:27 PM.
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Old 07-05-2021, 10:19 PM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
Join Date: Jul 2009
Location: Mojave
Posts: 4,833

Slick. Thanks for posting this. Its now filed away in my brain for use in the future.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
Harmon Rocket II -SDS EFI
1940 Taylorcraft BL-65
1984 L39C
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Old 07-05-2021, 10:52 PM
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PaulvS PaulvS is offline
Join Date: Aug 2019
Location: Western Australia
Posts: 718

Thanks for sharing a good idea, it beats buying ten 12 inch extensions.
Paul vS (yes I'm also a Van)
Building RV-6A #22320 O-320 FP. Wings and tail complete, working on fuselage
Flying my Aeroprakt A-22 STOL and the aero club's RV-9A while I build
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