Ugh, I really need to get on top of my work ethic. Two weekends ago I was out of town, that’s a valid excuse. The weekend after that? Yeah, there was stuff to do around the house, but I didn’t make time to work on the plane. Though I think the real issue is me never working on weeknights – really, I think those were as much of a contribution to forward progress as longer weekend work sessions. Maybe tonight will be the start of weeknight work sessions again, guess we’ll see.
So all I had left to do tonight was to drill those last two inboard bracket holes, followed by the four holes for the inboard wear plates. I ordered four 5/16” bits, just to make sure I’d have spares if I had problems with bits breaking again. So of course, this time I drilled both of the holes without breaking a single bit. Guess I’m probably set on 5/16” bits for quite some time…
That just left the 1/4” wear plate holes. What makes these fun is that they’re match drilled using existing holes in the inboard gear weldments – that means they’re drilled from inside the cabin, aka drilling upward since the fuselage is currently inverted. I’d previously kinda considered flipping the fuselage to drill these, but that would require me to remove the gear legs, reinstall the inboard brackets, and then flip the fuselage to drill. That seemed like unnecessary work to me, so I drilled from below instead.
This was where my judgment kinda went south. Once I was lying under the fuselage, I realized it was difficult to tell if I had the drill square to the weldment. The first idea I had was to start each of the four holes, then remove everything and finish the 1/4” holes on the drill press where I could ensure they were square. But then I got worried about the potential for the holes to wander a bit, so I decided to just finish the holes from below.
Here’s the problem with doing this – it’s best to drill each hole in one shot, because heating the steel at the tip of the bit and then letting it cool can result in a local heat treating effect, hardening the steel and making further drilling challenging. Once I started drilling the holes completely, I got through the first one OK, but on the second one, I hadn’t made much progress at all when I stopped getting chips out of the hole. A look at the tip of the drill bit showed that it looked to have dulled. Well, that’s what the spare is for – I switched that one in, and finished the second hole, but got the same result with the third, a bit of progress followed by a complete stall.
Another part of the problem here was that since I was drilling from below, there was only so much pressure I could put on the drill – eventually I’d just lift the front of the fuselage off the sawhorses, which seemed like not the greatest idea. What if it moved laterally when I did that, and missed the edge of the sawhorse when I put it back down? That’d be bad news all around.
So I decided to go with my original plan for that second wear plate. Using the drill press would give me more control over the hole, and maybe I could make it through with my one remaining 1/4” bit. So I pulled the gear legs, took the wear plate over to the drill press, and sure enough, got the holes drilled with little drama. (It probably helped that it was a lot easier to lube the drill bit this way)
That just left the moment of truth – would the holes line up? Good news – they did. After that, I set about cleaning up – there were loads of metal shavings all over the fuselage and the floor around it, oily parts from the Boelube I’d been using, and holes to deburr to boot.
So now it looks like I get to skip back to fitting the forward bottom skins…tomorrow, I guess.