Countersinking Nutplate Screw Holes

I was able to wrap up all of the fuel tank attachment nutplates and the inspection cover nutplates tonight.  In the last session, I installed all of the nutplates, and tonight I finished them up by machine countersinking all the screw holes to accept the dimples in their mating metal.  The work started out by first setting up my microstop countersink with a #30 pilot in the #8 nutplate screw holes.  Van’s has a pretty good tip on getting this depth correct:  Cut the head off a #8 screw and use it as a guide.  Once the screw head sits flush with the surface, go a few “clicks” deeper with your microstop so there will be enough depth for the dimpled metal.  Here is my homemade “gauge”:

It worked really well.  A lot of builders go out and do some weird things using dial calipers, and other extremes, but the main spar has a lot of metal and so long as you go just slightly deeper than the screw head, it’ll be perfect.  Here’s a good shot showing how it looks with my “gauge”

You can just barely see the fresh aluminum around the head of the screw. To give it a really good test, I used some scrap sheet aluminum the same thickness as the tank, drilled and dimpled a #8 screw hole in it and made sure it would nest into the countersunk hole flush.  It did, so I locked my microstop down at that setting and countersunk all the other fuel tank attach screw holes on both spars.

The next bit of work was to countersink the screw holes for the inspection cover nutplates.  Theres three inspection covers on each of the underside of the wings, and the forward 4 holes are all attached to the main spar with #6 screws and nutplates. I did these pretty much the same way as the #8’s above.  I cut the head off a #6 screw and used it for my gauge, then set my microstop a few clicks deeper and countersunk a test hole.  Then I grabbed one of the inspection covers, drilled it to size, dimpled it and laid it across the spar to make sure it seated flush against the spar.  I had to tweak the counterisnk a few more clicks deeper, but finally ended up with a nice flush fit, and then locked it down to do the remainder of the holes in both spars. Heres how the inspection cover looked against the spar:

Finally, the last thing to do was to prime these new countersunk holes.  The spar ships anodized, and drilling the countersinks leaves the metal in those spots open to corrosion. Vans recommend that we prime these spots to prevent corrosion.  So, I mixed up 10 mL of AKZO (5 mL of each of the two parts) and let it sit the required 30 minutes for induction.  In hindsight, 10 mL was a bit too much, I probably would have been just fine by mixing about 5 mL total.

Yep, thats a high tech paint applicator and mixing cup…courtesy of Q-tip and Gerber baby food. I used about 5 Q-tips to apply the primer after it had inducted, and the worked well enough.  I got a little messy with the application on purpose, as I wanted to fay the primer out from the holes to ensure there was no edges that moisture could penetrate.

I made sure to get decent coverage on all the countersunk holes, and then called it a night.  I’ll let this stuff cure until tomorrow and then start another session.  It looks like I’ll be building the tie-down brackets!  Here’s all the photos from tonight:

Google Photos Link:

Hours Worked: 4.25

Started the Wings! Countersinking for the Nutplates

Today marks the official start day for the wings! I have been studying and reading over the plans since the wing kit came in last week. After getting the shop organized and setup for the wings, I decided tonight was as good a night as any to get started.  Of course, the first thing Vans has you do is go drilling and countersinking hundreds of holes on these gorgeously expensive Main Spars.

The plans has us first attaching the nutplates for the wing tanks.  The wing kit instructions are very…..spartan.  We are told that at this point, Vans expects us to know how to do things so instructions are basic workflow guides.  Luckily, the empennage kit prepares us really well for the work and I am now pretty comfortable at reading the plans to find out what rivets, nutplates and orientation they need to go.  The first step is to tape up the gap between the spar flange and the spar bar / doublers to keep drill shavings from going in and causing damage.

There is A LOT of holes for these things.  I think its somewhere around 150 holes that need to be drilled and countersunk.  I started off match drilling all the mounting holes for the K1100-08 nutplates.  They use AN426AD3-4 rivets, so I drilled them all to #40.  Reading ahead in the plans, I also noticed that I need to also drill #40 holes for the K1000-06  nutplates that attach the W-822 access plates to the main spars, so I got those holes done as well. I started on the left main spar, then moved over to the right main spar to do the same.

Next up was the countersinking.  I chucked up my microstop countersink and put in a #40 bit.  I backed the countersink all the way out and worked my way up on a test hole until I had the correct depth, then countersunk the first hole in this expensive piece of aluminum.  I dropped in an AN426AD3 rivet to see how it fit, and a few more clicks of the microstop had it at the perfect depth.  Then I done the rest of the bazillion mounting holes for the nutplates on both spars.

Test rivet fits so snug and flush!

You really have to be careful doing this as there are tons of holes, and the diagonally mounted nutplates in the wing walk area can make you scratch your head a bit.  Having done all those, I decided to do the next sets of nutplates which is on the front of the main spar, where it mounts to the center section.  I gave the plans a good study to make sure I was correct on their orientation (the K1000-4  nutplate itself  gets mounted on the forward side of the main spar), I match drilled #40 and countersunk the AFT side of the both main spars.

After 2.5 hours of drilling and countersinking all these holes, I decided to call it quits for the night.  I still need to countersink the actual screw hole for the nutpates, but can’t do that until I have the actual nutplates riveted on to the spars.  That will be a good place to start for the next work session. I noticed there are three more holes for nutplates in the spar doubler, but I am not sure what they go to.  I will look the plans over tonight and get them tomorrow.

Here’s all the photos from tonight:

Google Photos Link:

Hours Worked: 2.5