Sun Jan 20 2008

Deburring bulkheads and firewall assy

I did these last two bulkheads late last night (another three hours) then called it a night.

After sleeping in (I love weekends), I went down to the shop to do more deburring. After looking at the pile of stuff I've deburred to date, I decided to do something fun today instead.

So I decided to start working on the firewall. Funny thing is that the first thing I had to do was (you guessed it) deburr the firewall. Even though the instructions warn that deburring stainless is difficult, I found deburring all of the firewall edges to be very easy. I just used a 1" ScotchBrite wheel in my die grinder. I almost think deburring the stainless is easier than aluminum, because the ScotchBrite wheel isn't as aggressive as on aluminum. And if you slip, you don't end up grinding the material just kind of polishes the surface a little.

The ends of the stiffeners had to be sanded down slightly and the corners needed rounded to fit into the notch in the gusset.

Mo' betta!

Where the center stiffeners meet the top stiffener, theres a slight interference where the radius of the top stiffener prevents the center stiffener from sitting down flat.

A little more filing and it fit right in.

I needed to fabricate the F-601E-1 stiffener that goes just below the firewall recess. They say to use AA6-063x3/4x3/4 angle for this. I found two pieces of angle in the fuselage parts that were six foot long. I figured that while I was cutting this piece, I might as well cut a few others. So after flipping through the plans, I came up with a list of parts that needed fabricated from this same material and came as close to six feet total as possible. Here you can see F-728B, F-729B, F-601E-1, and F-729C after cutting. The scrap piece was only about 3/4 inch long. That's what I call minimal waste. :-)

I spent about a half hour looking for the right piece of material to make this doubler from. The only piece of .063 thick 2024-T3 I had was a lot larger than this. That'd definintely work, but I was unsure if perhaps it was meant for some other part later on. So I went to do some research on the net. That turned out to be a good move because I learned that this doubler is only needed if you're planning on installing a carburated engine. Mine will be fuel injected, so I didn't have to bother making this part at all.

Sooo....back to work on the firewall. I drilled the F-601E-1 stiffener that I had previously fabricated...using the prepunched holes in the firewall as a guide, of course.

The floor attach brackets needed a slight radius filed on the outside corner to eliminate interference with the center stiffeners.

These spacers go in the upper corners of the firewall. They also needed a radius filed along one edge to eliminate interference with the radius of the diagonal stiffeners. Note that I didn't drill the #30 hole like the plans indicated. I decided to match drill that to the firewall later.

Once I did that, I match drilled two of the three holes to the firewall and diagonal stiffeners. The #30 hole will get drilled later.

These angles need to be spaced 3/32 inch from the bottom stiffener. I saw this idea on Brad Oliver's site to use a #40 drill bit to get the 3/32" spacing. The long #40 bit was long enough to set the correct spacing for both angles.

Match drilling these brackets is actually pretty tricky. After some thought here's what I decided to do: First I clamped the bracets to the bottom stiffener and firewall. This required a small wood block on the forward face of the firewall so the c-clamp didn't crimp the flange of the firewall. Then I flipped the firewall over and drilled two holes through the bracket using the prepunched firewall and stiffener holes as a guide.

After clecoing those two holes, I removed the clamp and used it to clamp the brackets to the vertical stiffeners...

...and removed the diagonal stiffener and spacers.

Now I'm ready to flip the whole thing back over to match drill the remaining holes to the firewall.

Voila! I made sure to use the reflection of the drill in the surface of firewall to ensure that the holes were going in nice and straight.

After that, I just reinserted the diagonal stiffeners and the little spacers and match drilled those.

After that I clecoed the firewall recess in place.

The side holes near the top of the recess didn't line up well to the firewall. They were pulled inward on each side by about 3/64". I thought about stopping and talking to Van's about the situation, but then decided it would be OK to just drill them and end up with oblong holes. The firewall recess isn't structural, so having a poorly fitting hole or two shouldn't hurt anything.

Here's a fiew from the forward side after drilling and clecoing. The hole in the stiffener and firewall is nice and round, but it made the hole in the firewall recess kind of oval shaped. Oh, well.

After much more drilling, clecoing, and more drilling, I had all the stiffeners drilled to the firewall. It doesn't really show in the photo too well, but it's a complete mess. There's Boelube and chips everywhere. The dang Boelube cap leaks, so every time I tip it over to put a drop on the drill bit, I actuall get two for the bit and one to run down the side of the bottle. Grrr.

Last task for the night was to put on the longeron attach weldments and match drill them to everything else. I've gotta say, it's nice actually having assembled and drilled some stuff rather than doing deburring. Tomorrow I'll probably take this all apart and deburr everything.