[jlfernan]

I have seen complaints about the difficulty of match drilling through the aluminum flaperon skins into the steel counter-balance tube. The bit tends to travel over the hard steel and elongate the hole in the aluminum nose skin. The following technique seemed to work pretty well for me:
1. Use a spring-loaded center punch to put a small crater in the middle of the hole in the nose skin (into the steel).
2. Then use a small bit (1/16") and drill through the steel. The small bit seems to find the crater and stay in it better than a #30 bit.
3. Then drill through the hole again with a #40 bit.
4. Then drill through the hole again with the final #30 bit.
The trick, I think, is using the very small bit to drill the first pilot hole through the steel tube because it stays in the crater made with the center punch.

I used this technique, but unfortunately for me, while the holes in the skin are round they are oversized. The holes thru the pipe are perfect, but the rivets have some wiggle room thru the skins. Any suggestions?

 

[DaveLS]

Here is the process that I eventually came to:

The very thin skin pre punched holes are #40s, so do nut use them to center a drill. Instead mark and center punch the tube. Dissemble, and drill out (high pressure, low speed, lots of cutting fluid to keep everything cool) the tube to #40 on a drill press using a V block, starting with a much smaller pilot hole in the center punch. Reassemble, and enlarge the skin and tube holes together with a #30 reamer if you like. This will make the skin and tube holes very close if not exactly the same. Disassemble and debur the tube. Here I used an internal deburing tool that a machinest friend of mine set me on to. It can be purchased from Mcaster Car, Small hole deburing tool, part # 7815A21,

http://www.mcmaster.com/#bur-tools/=o837aj

Finding this combination took, after many false starts, over six months.

So Jorge, if your skin holes are too large, you could try again with new skins assembled over the already drilled to #30 tubes. If when assembled all that you can see through the #40 skin holes is the #30 tube holes (that is no tube) you would be good to go. Reaming out the skin to#30 when mounted on the tube, would allow the tube holes to guide the reamer in the skin. Just an idea.

Furnishing these tubes, the center section, and longerons (also pre bent)with all the holes drilled would be really great for us novice builders and facilitate the s-lsa factory build. I don't need no E-AB 51%. Just sayin ........

-Dave

 

[XOverZero]

...Here I used an internal deburing tool that a machinest friend of mine set me on to. It can be purchased from Mcaster Car, Small hole deburing tool, part # 7815A21...

Second on the deburr tool from McMaster-Carr. Cleaning up the holes' inside edges in the stainless isn't real easy. The burrs are big and tough and jagged, but this tool and some patient application therewith gets the job done. Watch out for one thing though. That microscopic little Allen screw that the blade pivots on strongly tends to back itself out. Lose it and you're finished. I recommend re-tightening it every three or four holes.

 

[jlfernan]

I had no issue drilling thru the stainless. Like I said before those holes are perfect. I just don't understand why the skin holes(I realize the skin is just "wafer" thin) are round but enlarged?

Here's what I have. The first pic shows a rivet in the stainless pipe. Nive and tight:

The second you can see the space around the rivet:

 

[rbibb]

I wouldn't sweat it. The counterbalance skin isn't really carrying any loads there and the purpose of the rivets is to just hold the weight into place and to hold the skin into its shape. I'd bet there are probably around 7,999 of the 8,000 RV's flying with the same issue. There is that one guy somewhere that managed to scrounge up a laser guided, CNC programmed drill machine that got it perfect. The rest of us just have a few imperfections hidden away...

Richard

 

[Jetguy]

I agree with Richard. This is not an aerobatic airplane. It's max speed is 120 kts. If you want, put some red locktite on underside of the head of the rivet and pop it in there. Wipe off any excess when done. By the time you build the whole Flaperon you will see that it's not a problem.

 

[Gandalf]

Second on the deburr tool from McMaster-Carr. Cleaning up the holes' inside edges in the stainless isn't real easy.

I had to use a combination of techniques to deburr the inside edges. I also used the inside deburring tool. I also used a smaller pipe to knock the burrs down. I resorted to a long wooden dowel with a sanding drum on one end and a drill on the other end.

 

[jlfernan]

I finally did the right flaperon counter balance. Took a few extra steps, but the results were worth it. Center punch, #40 drill(drilled it all in place), 7/64" bit, #31 reamer, then #30 reamer. Lots of cutting lube. Perfect holes. I had a friend come over, A&P, retired quality control inspector for airline maintenance, RV-8 builder and also building a -12. He concurred with those here that the holes for the left flaperon were OK. So that's how I leave it. Thanks for the help.