Countersunk Left Main Spar, Drilled Left Rear Spar

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Well, I managed to motivate myself out into the garage a little this weekend.

I only have a few more steps on the left main spar, and the the left rear spar, before I really need to get my butt in gear with the rib deburring and finally build a wing stand.

Today, I focused on countersinking the screw holes for the tank attachment.

Reading back over my own old post (in which I reference some other builders), I found this table. I’ll copy it here, too.

Countersink Widths for Numbered Screws Screw Size Width [in] #6 <0.3125 #8 0.365-0.375

So, I broke out my trusty digital calipers, zeroed them out, and dialed in .312.”

Sorry for the blurry picture.

So, with microstop countersink cage on the front of my drill, I got to work. Here are the smaller countersinks for the #6 inspection plate attach screws on the bottom flange of the left spar.

Pretty countersinks.

Then, I moved up to the 0.370″ countersinks for the larger #8 tank attach holes.

Looking good.

Somewhere in here I flipped the spar over and finished all the countersinking on the upper flange of the left spar.

Sweet.

After the countersinking, I scrounged up the left rear spar and corresponding doubler plates.

Left Rear Spar, reinforcement fork, and doublers.

Per the plans, I grabbed the W-707E and aligned it 50 3/4″ from the outboard edge of the rear spar.

I promise it is right at 50 3/4". I think the paralax make it look off.

W-707F is laterally aligned with the outboard edge of the rear spar channel.

W-707F is clamped and ready to matchdrill.

Here’s W-707E, ready to drill.

After drilling one #30 hole.

All done.

Then, I moved outboard to W-707F.

Before matchdrilling.

All done.

I call this the forest of clecos.

I moved inboard and matchdrilled all of the reinforcement fork holes.

A lot of drilling.

I pulled the doubler plates and reinforcement fork off and set them aside.

I still need to drill out the aileron pushtube bracket hole.

Reinforcement fork pulled off.

Next up, deburr all parts, along with finishing any last minute tasks like dimpling where I can’t reach later, then prep for priming, prime, and rivet the rear spar together.

1.5 hours.

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