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| My deburring kit. Simple, but effective. |
For deburring the holes in the skins, ribs, and spars, I used the deburring bit that came with the Cleaveland tool kit. It has a hex shank, making it easy to attach to my electric screwdriver and making for a very easy deburring process. All it took was a one-second button press per hole, and I had very clean, slightly chamfered holes. The only downside is that the constant start-stopping of the screwdriver killed the battery pretty quickly, so I had to recharge it halfway through.
While waiting for the screwdriver to recharge I tackled the task of countersinking the bottom holes of the VS-808PP spar doubler. The bottom of the spar sits flush with the fuselage, so the lower 22ish holes in the assembly need to be dimpled on the VS-803PP rear spar and countersunk on the spar doubler to allow for flush rivets to be installed.
I had been a little nervous about countersinking since I had never really been taught the proper way to set up the cage. My past attempts on practice pieces had yielded poor results, so I watched a few videos on the subject before attempting to do it on my airplane. I set the countersink cage using some scrap left over from my earlier mistake on the horizontal stabilizer. All I did was start with the cage set to barely make a countersink, then slowly increase the amount of material cut away until I could get the appropriate rivet to sit flush in the hole.
There will be a spar sitting on top of this countersink, however, so the rivet actually needs to sit around .007" lower in the hole. I have no way of measuring this (that's a little more than 1/128"; I mean, really?) but a few of the videos I watched mentioned that the proper depth would yield a very slight ring of polished aluminum showing around the head of the rivet. An eighth of a turn further on the countersink cage gave me the ring I was looking for.
I cautiously took my now set countersink cage and went to countersink the first hole in the spar doubler. By not applying too much pressure and just allowing the weight of the drill to rest on the piece, the hole makes a slight chatter while being cut and the chattering stops when the cut is complete. Testing with a rivet showed the ring I wanted. To test the depth I dimpled the corresponding hole on the rear spar (using my new DRDT-2, this thing is soooo nice) and fit the pieces together, then put a rivet in the hole to check the overall fit. It works!
I went to work countersinking the rest of the necessary holes and felt a feeling of accomplishment and newfound confidence once I had finished. Now that the cage is set for the #30 countersink, I'm considering just buying another countersink for the other size holes just so I don't have to reset this one every time I need to change the bit.
The screwdriver had finished charging by this point so I used it to deburr the remaining holes. And just like that, work on the VS is done (for now). With the relative speed and ease of assembling the vertical stabilizer compared to all of the odd little tasks done on the horizontal stabilizer, I'm surprised the plans don't have builders begin with the VS. Interestingly, RV-10 builders actually do work on the VS first (that's Jason Ellis's YouTube channel, by the way; his build videos are super informative and entertaining and were a huge influence on me when I first decided to build an airplane).
At this point the only things left to do on the VS are to prime, dimple, and rivet in that order. I'm taking the suggestion to prime the parts before dimpling to make it easier to scuff the surfaces and shoot the primer without the dimples messing up either my Scotchbrite pads or the primer application itself. The AKZO epoxy primer I'll be using is supposed to be pretty damn hard to scratch or remove after it's cured, so I should have no problem dimpling the holes after the primer is applied.
Work on the vertical stabilizer took a lot less time to complete than I expected, so I started work on the rudder while my replacement HS spars were still in transit.
The first step in building the rudder is the most tedious – fabricating the stiffeners. Here's the process I used:
1) The preformed R-915 stiffener, one of eight.
2) Cut in half at the prepunched marks using the hand shears (the piece is too long for the bandsaw).
3) Remove blue vinyl.
4) Use the bandsaw to cut to the desired length (R-915A leaves all 18 holes, and each subsequent stiffener removes one more hole until R-915H which only has 11 holes) while leaving at least 1/4" of material on each end for minimum edge distance for the rivets. This one is an R-915D, so 3 holes are removed from the forward end of the stiffener.
5) With the shears, trim the forward end per the plans by cutting from the center of one notch to the center of the other notch. This is easy to do on the R-915As since the notches are already there, but this is the end that gets removed when shortening the piece for each new stiffener. I used a cut-off piece of scrap R-915 as a template and traced the notches onto the shorter pieces.
6) Grind the edge to its final length (remember to leave 1/4" for rivet minimum edge distance) and remove the burrs using the Scotchbrite wheel. It should be a smooth transition from one edge to another, without any sharp corners.
7) Draw the cut line from each notch on the aft end of the piece. This will be the part that fits into the aft end of the rudder.
8) Trim the excess material using the band saw. The hand shears work too but may deform the piece, so I prefer the band saw.
9) Smooth the edges and grind to the cut line using the Scotchbrite wheel. This is easily the most tedious part since grinding the material is slow and you've got to keep the edge straight the whole time. Then, round the corners and remove any burrs.
10) Repeat for each stiffener. Oh, did I mention that you have to make 16 of these things? This will take a while...
