Ok, so countersinking and setting the fuel tank nut plates is taking me way longer than it should, but for good reason.  I spent quite a lot of time experimenting, fine tuning and researching the correct method.

There are essentially two methods one can use to countersink the holes for the #8 screw that will attach the fuel tank to the nutplates installed on the spar.  Its also important to note that the outside diameter of the countersink should be 0.375 inches.  (Good references can be found here.  And here.)

1. Van’s Method:  According to the instructions, you can dimple the rivet holes and then install the nutplates prior to countersinking the center hole for the #8 screw.  The reason you want to instal the nutplate first is that the #30 countersink can “chatter” and cause an oblong or deformed hole as the pilot has no hole to guide it and keep it centered.  The installed nut plate acts as that guide.  I tried this on two separate installations, and it resulted in a perfectly centered countersink.  What I did not like, however, was the impact to the nutplate.  The rotating countersink caused just the most minor of wear on the threads inside the nutplate.  I tested both with a #8 screw and compared them to nutplates that had not been used yet.  It was definitely harder to turn the screw in the two nutplates that had been used as the guides for the countersink.  Do I think this would be a problem?  Actually, probably no.  But it does increase the risk of cross threading a screw, and I don’t want to take that risk.  And for this reason alone I went with option two…
2. Chokoway Method:  I think thats what this is called, and I assume named for a builder I’ve never met.  Anyways, this method has you make a countersink guide plate and hold that plate under the countersinks with clamps.  I used an old piece of aluminum angle, drilled with a #30 drill bit.  This method works perfectly for producing a nicely centered countersink.  The significant downside is time.  You have to unclamp, align, and reclamp for every countersink… and there are a lot.  I would estimate this method takes three times as long as the Van’s method.  Regardless, I prefer this method.

I have all of the rivet countersinks complete, and about half of the center countersinks complete.  Once I have completed all of the countersinks, riveting the nutplates in place will be very quick and painless.

I’ve also been rearranging my shop and trying new things to optimize my time.  The wings require reference to multiple schematics at once, which was not the case for the empennage.  My lone schematic easel is not sufficient, so I just tacked up the other two that I currently need.  I taped the preview plan version of some of the other schematics up on the right for quick reference if needed. 

My last project for the day was the shipping crates.  We have a farm, and on a farm you never throw good wood out.  You never know when it might come in handy.  I keep a large pile of scrap wood and misc building supplies in the equipment shed.  I decided to put both the crates there until I figured out a good use for them.  Since I already had the tractor out, I decided to make the task that much easier.  So much less work to move and stack large items when you’ve got a front end loader and a chain!

I did an inspection, marked the spars, and began figuring out what the next step is. The answer is fuel tank nut plates.  I messed around with several setups before I found one that I like, and began final drilling the attachment holes.  In the process I actually broke a countersink bit!  I also did a major clean up of the garage and some more organization.  I should be able to get some real work done on the spars in the next session.