One of the reasons I couldn't start as early as I wanted on section 14 was this:
This beautiful bobcat was sitting right next to the shop entrance and wanted to take a nap, so I backed off and let her be. I love cats and wild ones even more, so I wouldn't do anything to make them feel anything but welcome....
Half an hour later she found a better spot and was gone, so back to work.
The job was to countersink (120 deg!) the outer side of the leading edge reinforcements that later get attached to the inboard side of the nose ribs. The skins in that area will get riveted on with CS4 rivets. Why that is I'm not quite sure as all the other skin rivets have a domed head. How this is going to be smooth I don't understand either as the holes in the skins are not going to get dimpled except for two on the outboard side of the skins. You see all that later in section 15. I can just assume that the particular way they want you to countersink this part (a bit deeper than you usually would) means that the force of setting the rivet will also do the dimpling and force the skin to bend enough to seat the rivet flush with the skin.
But that's in the future! For now, I had to figure out how to actually do the countersinking on a piece that cannot be sit flat on a surface to work on. The flange of this front spar is bent to match the curve of the skin in this area. I tried first to use my trusted electric screwdriver that I used before with success on parts that are flat. This worked OK until my arm got tired and I had a hard time to hold it perpendicular to the surface (that flange area is very small). I hadn't even finished the 28 holes on one flange when that happened so I had to think of something else.
I laid the flange flat on the edge of the workbench and moved the hole to work on just beyond the corner of the bench. Now I could press down straight and work as usual while my weak hand was holding the flange in place. The spar material is thick enough to withstand the force without bending or flexing. After doing about 3 or 4 of the holes with this method I thought that if I could just find a support with sharp and straight edges I could do this on the drill press and safe myself a lot of muscle pain. After all, the number of holes to complete this task is 112.
I found a V2A steel cube that with some extra support had a reasonable height to give the web of the spar enough clearance on the drill press platform and I tried it with good success. For a reason that I still don't understand, the countersink cage sometimes starts vibrating in the hole and then creates a larger countersink than what it was set to. This happened twice while using the drill press and it is announced by a sound of screeching metal. All you have to do then is to stop, apply a drop of Boelube on the hole and continue carefully. Unfortunately, I learned this after messing up two holes and sinking them too deep. Not too much to throw the part away but enough to be unhappy with the job, so safe yourself the grief and be careful.
After I found out how to use the drill press in this step, I was making a lot of progress and finished the second flange in record time and without tiring my muscles.
This is the result of 3.5 hrs of countersinking and trying different ways doing it.
Here's a photo of the final setup:
Tomorrow evening I'll try to do it to the second spar.
No comments:
Post a Comment