Sat Mar 8 2008

Battery box and relay mounting

We had a blizzard going outside today, so it was a good day to stay in and work on the plane.

I started laying out the relay locations. It appears I'm going to have to trim one of the flanges to eliminate this interference.

I laid out the location of the doubler plate as a double check that the layout in the plans would work OK. I chose to do this because as a designer, I know that purchased components (like the relays) are notorious for changing mounting locations without notice. I wanted to make sure the holes were going to be in the right place before drilling anything.

Looks good!

I fabricated the little doubler plate and drilled the holes to #40.

I drilled the first hole for the nutplate to #40, clecoed on the doubler and match drilled all the other holes to #40.

In order to drill the 1/4 inch holes in exactly the correct location I needed a template. What better template than the nutplate itself. I drilled one out to use as a drill bushing.

No more threads. :-)

I clecoed one side of the nutplate to the existing hole, match drilled the #40 hole for the other side of the nutplate...

...and drilled through the whole shebang with a 1/4 inch bit. The nutplate was kind of squeezing the sides of the bit, so I used lots of Boelube. It still got really hot though.

The first hole came out quite nicely.

After doing the same thing for the nutplate that goes on the other stiffener, it was time to drill the nutplates through the doubler. I double checked all the layout lines and found that the pilot hole for the bottom nutplate in the doubler was about 3/64 inch too low. You can see the correct layout line just skims the top of the hole.

After drilling the other two holes using the match drill through nutplate method, I dimpled (almost) everything. There are two holes which are too close to the existing holes to use my regular dimple dies. I ordered a close quarters dimple die from Cleaveland Tool. I'll dimple those last two holes when it comes in.

Note that when I drilled the bottom 1/4 inch hole through the doubler, I had the aluminum doubler on top of the firewall. Thus when the drill bit penetrated the aluminum and started to drill through the firewall, the pressure of the drill distorted the firewall material somewhat. It also made an ugly burr. I did the best to clean it up and flatten it out, but you can see it's not as nice as the top hole.

After a nap I decided to drill the holes for the battery box mount. I did the top hole near the firewall recess first. This hole came out really ugly because the #12 bit dug in and left a big nasty burr in the sheet metal.

So for the second hole, I decided to sandwich the sheet metal between the lower stiffener and a scrap Z-bracket.

As you can see the second hole came out much cleaner. The moral of the story is: For drilling large holes in the thin firewall, be sure to sandwich it between two thick pieces of aluminum.

I clecoed through the two bolt holes on the right side of the mount.

With those two clecos in place I could see that the left side bolt hole didn't line up exactly with the rivet hole. I drilled it anyway and it came out OK.

I took a minute to place the relays in position. It all looks good. As much of a pain as mounting these components is with the firewall on the bench, I'm sure glad I didn't wait until the fuselage was assembled to do this. I'm guessing the difficulty would have been much worse.