With all the match drilling done on the gear towers, next it’s time to do a bunch of countersinking and dimpling. Actually, I get to do a lot more dimpling here than the plans specify thanks to my removable cover mod, since I’m using flush screws there.

Most of the countersinking per the plans is on the right gear tower. All the rivets on the forward side get flush rivets; from what I can tell from the plans, this is because the rear wall of the forward baggage area rests against the gear tower. There are also some nutplates on the forward side, which I imagine are also related to the baggage compartment. Anyhoo, lots of countersinking:

Next I moved on to dimpling the tower cover and the dubbers I fabricated. Here I realized that I’d made a slight error when making those doublers. When I laid out the screw hole locations, I neglected to leave room for mounting the nutplates:

This isn’t really a huge deal though, because there are single-side nutplates available, as seen here:

Problem is, I only have a couple of those on hand. They came with the kit and will presumably be needed dow the road, but I don’t have enough anyway. Which means I get to order more stuff from Spruce. I’m pretty sure I’ll end up paying as much for shipping as for the actual parts, but that’s the way things go, I guess. Kind of makes me wonder: out of all the money poured into an RV build, how much of that was repetitive shipping costs from places like Spruce? Probably more than anyone wants to consider…

Anyway, then I moved on the dimpling the covers themselves. The fun thing about this is that the large screw dimples also warp the material, so after dimpling I get to flatten the material out again. It was mildly annoying on the doublers, but slightly more obnoxious on the covers:

Finally, I dug out my #8 screw countersink bit and countersunk the angles to fit under the dimples on the cover:

The only thing really remaining on these parts is to drill and countersink all the nutplate holes for the covers. Maybe I can get that done tomorrow night.

Tonight I just caught the left tower up to where I got the right tower on Sunday; cutting the face into three sections, fitting and drilling the doublers, then finally clecoing everything together and getting everything match drilled.

The whole thing clecoed together:

Detail of the upper doubler (the photo isn’t crooked, there’s a slight angle to the cut here):

As mentioned last night, today’s weather was gorgeous, so my main objective was to get the parts for the forward floor and cooling ramp primed. But that took hardly any time at all, so I spent most of the day working on the right gear tower. I’m modifying my towers, as many other builders have, by making part of the tower face removable. There’s quite a bit of work that has to be done inside these towers, from riveting stuff together in the near term to routing fuel lines and torquing gear bolts in the long term. Normally, all of that work would have to be done working through the lightening holes – not a fun prospect.

The basic idea for this mod is the cut the tower face into three sections, making the center section into the removable cover. The existing rivet holes are drilled up to #19 for #8 flush screws, and doublers are fabricated to allow for nutplates at the top and bottom of the cover.

Here, I’ve marked the cut lines on the right tower face. My initial plan was to make the cuts using a special thin cutoff wheel in my Dremel, so as to minimize removed material, which would leave a gap between the pieces later on. But that didn’t work out to well; the wheel kept binding in the cut, and about the third time this happened, the flexible shaft I as using snapped. Can’t really make these cuts without that shaft, so this was a problem. But after making a test cut in scrap with the bandsaw and comparing, the amount of kerf was essentially identical between the cutoff wheel and the bandsaw. So I just did the rest of the cutting with the bandsaw.

Cut are now finished. To the left is the top of the gear tower. The center piece will be the removable plate, and the right piece will be concealed behind the inner gear weldment.

All three pieces clecoed to the corner angles so I can fab and fit the doublers.

Doublers fabbed from .040 alclad and marked for initial rivet holes.

Rivet holes done and match-drilled to the tower face sections, time to fit the cover plate.

After clecoing the cover plate on, I clecoed the entire tower structure together and match drilled all of the holes, then drilled the cover plate holes out to #19 for the screws. I meant to take a photo of the assembly, but I forgot until I’d already torn everything apart and started deburring, so all I have is a picture of a pile of parts:

I still need to dimple/countersink a bunch of stuff, in addition to drilling all the nutplates for the cover attachment. And then I have to repeat all of this for the left tower. 

Didn’t get out and working until late in the afternoon today, but I did do my first solo tailwheel flight this morning, so it was still a good day. I started out by continuing prep work on the forward floor that I’d clecoed together last night. Basically just a bunch of match drilling, deburring, dimpling, countersinking. Once again I got carried away while dimpling the skin. Only some of the holes get dimpled for flush rivets, but I got in the groove with the C-frame and at some point abruptly realized I’d dimpled five holes that weren’t supposed to be dimpled. At least dimples can be flattened, unlike countersinks which have no such “undo” potential.

Clearly this is something I’m going to have to work on with the fuselage; slowing down a bit and taking care with what I’m doing. To avoid a repeat of my countersink error from the firewall, I made sure to mark the floor braces so I could see the limits of what needed to be countersunk:

With all the forward floor parts prepped and ready for primer, I moved on to the cooling ramp. This is a simple assembly, just a skin piece and two stiffeners. Except first you have to find the (fairly small) stiffeners in a giant pile of parts. I dug around for a solid 20 minutes before I got so frustrated that I decided to cleco together the gear towers instead. (my flimsy rationale for this was that maybe I’d find the stiffeners while setting out the gear tower parts)

These things are pretty sizable:

Surprisingly enough, my tactic worked, and after finishing with the towers I found the stiffeners in short order. The first thing to do on the ramp is to trim the skin a bit. And here is another one of those “why wasn’t this just made like this from the factory” moments. Beats me.

Then it was another round of clecoing stuff together, match drilling, deburring, dimpling, etc.

And now I have a pile of parts ready for primer tomorrow. I guess I’ll actually do some work on the gear towers tomorrow too in between priming and so forth.

Started out tonight by breaking out the C-frame and dimpling most of the rivet holes in the firewall. All these holes will get flush rivets on the forward side. There are a handful of the holes that don’t get dimpled, though; four of them are where a spacer sits on the forward side, and the rest are where two nutplates sit on the forward side. Next I moved on to countersinking all the firewall angles to match those dimpled holes. This went well, except for the part where I countersunk one hole too many:

Yup, that’s one of those holes that doesn’t get dimpled, so it shouldn’t be countersunk on the angle either. Welp, another piece for the scrap bin.

After wrapping up all the countersinking, I set the firewall aside – no more work on that until I get the replacement part from Van’s. So I moved on to the next step, which is the fuselage floor. All I really intended to do was to gather the parts and cleco them together, but once again, it took forever to find some of the parts. But I finally found them, and here’s that assembly clecoed together:

And that’s all for tonight.

Short session tonight, mostly cause I’m tired. I pulled all the angle/reinforcement pieces back off the firewall again, deburring the rivet holes as I went. Nest up was deburring the rivet holes in the firewall itself. Most of these – that is, the prepunched holes I match drilled –  were pretty straightforward, but the 1/4” holes I drilled for the rudder mounts were truly ugly. I’m not even sure you can call what I had on those holes a burr, it was more like a lip. So instead of just hitting those with the deburring tool, I manually sanded them down the the Dremel and flap wheel, ran the 1/4” bit through them again to ensure they were still sized OK, and finished the the deburring bit.

The last order of business was to put a required bend in the firewall. The upper portion is bent eight degrees forward, I believe to facilitate a better fit with the cowling. The instructions are pretty useful here, providing a good method. I used my digital level to gauge the bend, which was really easy. Compared to the aluminum sheet I’m used to bending, the stainless is pretty soft and doesn’t have a lot of springback. It was pretty easy to get an acceptable bend:

Next up is a whole bunch of dimpling and countersinking. Seems like this firewall assembly should be together in no time!

While I’m waiting on my stuff from Spruce to arrive so I can red rill the inboard flap hinges, I went back to work on the firewall. Most of my time tonight was spent deburring all the angles and stuff; the angles themselves are pretty complex, with lots of little nooks and crannies, so they were a bit tedious. And then there was smoothing the edges on the firewall itself. That piece is stainless steel and that stuff is kind of tough. I used a brand-new flap wheel in the Dremel and the wheel was pretty much toast by the time I was done.

Then I clecoed all the angles, engine mount weldments, and reinforcements in place, and went to town match drilling. The match drilling went pretty well; I was expecting it to be tough based on how tough the deburring was. That gave me a bit of a false sense of security; the next task was to drill two 1/4” holes through the firewall, which will presumably be used for mounting the adjustable rudder pedal assembly. Turns out there’s a big difference between slightly enlarging an existing hole and making a new (and large) one from scratch. Even using lots of lube, it took some time to get through the stainless.

Here’s the firewall assembly after match drilling:

Tomorrow I get to take all that apart again and do lots and lots more deburring…I bet deburring the stainless is going to be fun too. I wonder if I have spare deburring bits around, I might need a new one after tomorrow!