Got a few more hours to work in the garage on my main spar. I continued to countersink the various holes on the flanges of my main spar. I’m sure I mentioned this in one of my Empennage posts, but I had previously had bad luck with the 3 flute countersink bits and opted to purchase some of the single-flute bits from Cleaveland tool. In each bag that have a warning that its easy to break the pilot off of these countersinks if you apply a side-load on the countersink. HA, I’m sure that warning is for other builders, not me!
Month: February 2018
Main Spar – Part 2
Picking up where I left off I get the J-Channel prepped for the next spar. This time I decided to pre-mark the 1/16 depth on the J-Channel to mark the alignment vs using my digital Caliper. Pulled out the edge-marking guide I purchased from Cleveland tool and made quick work of it.
Basically a rinse-repeat of the previous update and quickly got the J-channel match drilled and set aside.
Next step was to get my countersink set up to make the appropriate cuts on the spar. Reading the directions, it took a while for me to fully understand what was being described in the text. Basically for ALL the nutplate rivet holes, you countersink them to just flush with the rib flange. (also there are a few additional rib attachment holes between the nutplates that area also just countersunk flush. Being slightly nerve-wracking I started SLOW and checked each countersink till I got more confident that I was doing things right. (As always I started with a TEST piece before I worked on the spar!)
Once both spars had this level of countersunk done (13-3 step 2), I reset the countersink to accommodate skin dimples and begin to countersink all of the remaining holes in the spar flanges (13-3 step 3). Easy enough and using a good countersink cage really helps to ensure you don’t screw up.
Once everything is countersunk, time to start installing the nutplates for the tanks. Again, nothing technically difficult but did take the time to make sure that my rivets really sat flush prior to squeezing. If they were just slightly proud, a turn or two with the deburring tool fixed the situation. (Also plans don’t call it out but be sure to deburr the inside edge of the spar web)
I ended up skipping 13-3 step 5 for now since I didn’t have the right countersink (on order currently) and moved to installing the nutplates for inspection plates. Again, nothing difficult.
EDIT: Before you laugh at me, I totally misread step 5 and ordered a #19 piloted countersink. Plans clearly state to “Drill a #19 hole and dimple for #8 screw. Countersink with a #30 piloted countersink.” Oops. Read more