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Drilling Elevator Trailing Edges

How were your holes for your elevator trailing edges? This is where you're using the pre-punched holes in the 0.016" elevator skin as a guide to drill #40 through the AEX wedge, bottom skin, and a length of angle. I'm having a heck of a time making the drilled hole concentric with the pre-punched hole, so I get misshapen holes.

I've already ruined my right elevator, so I'm using that as a test article for my technique while I await new parts (and a practice kit for further practice). I drill a 3/32" hole normal to the upper skin, then try to drill #40 through the parts all clamped together using my 84º drill guide block. The best hole I've made is about 0.118" in the upper skin on its widest aspect, larger than 0.103" per the mil-spec, and not concentric. I know the rivet will expand to fill the void, but that seems like a lot. I wouldn't accept that elsewhere on the airplane, and the trailing edges seem like a critical area. I know I'm drilling it at an angle, which will cause it to be somewhat elliptical, but I would expect the widest part of the hole to only occur in the fore-aft direction, and it's not consistently there.

Any tips or suggestions for how to drill these holes?
 
Followed the plans

When I drilled my elevators, I did as the plans said, with everything clamped together, and drilled #40 using the 82 degree template guide. I didn't have any problems. The hard part for me was countersinking the wedge.

Perhaps the initial 3/32" drill hole is giving the problem?
 
Thanks, Geoff. Did you center-punch the AEX wedge through the hole in the skin before you started drilling? Did you use a relatively fast or slow speed when you drilled? I really hadn’t thought drilling these holes would be this much of a challenge, given how many thousands of holes I’ve drilled so far.
 
Glue?

I used an industrial equivalent to shoe goo to glue the assembly area together prior to drilling. Clamped, let it set, then drilled after cure, cleckoing to the table as I went. No chatter or weird holes. I used the same holes in the table when I prosealed it down before final riveting. The shoe goo cleans up with acetone.

Getting good c/s on the AEX with no chattering was a PITA though. Cutting fluid (tap ease) and a used c/s head worked best for me.
 
Thanks, Geoff. Did you center-punch the AEX wedge through the hole in the skin before you started drilling? Did you use a relatively fast or slow speed when you drilled? I really hadn’t thought drilling these holes would be this much of a challenge, given how many thousands of holes I’ve drilled so far.

Didn't centre punch the wedge, I just marked the centreline per the plans and ensured it was clamped in position. I might've started the drill slowly but then went fast speed but light pressure.
 
Photos

Here are two holes I drilled today with a new #40 bit with the air turned way down and with fairly light pressure. The first one (10) is 0.129" on its longest aspect; the second one (11) is about 0.118". The holes in the AEX wedge are 0.980" (removed from between the skins), right where they should be.

I know that drilling it at an angle is going to make it a little bit oval, but this doesn't seem right.

link to album

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Another Mistake

I developed a drilling technique that gave good results, and I started working on the left elevator trailing edge. While drilling the first couple of holes, I managed to walk off of the fastener line, so now with a cleco in the outboard hole in place, the fastener line no longer lines up with the rest of the holes outboard of the middle hole:

The misaligned hole is on the left in this image.
Same two holes with a cleco in the drilled hole -- see how the fastener line no longer runs through the middle of the other hole.

I think these are my options, and I'm interested in any suggestions:

  1. Drill it the rest of the wedge the way it is, with the outboard side slightly misaligned. I'm concerned this might introduce a twist in the trailing edge.
  2. Realign the wedge so the fastener line lines up with the remaining holes, countersink the wonky hole as it is, and accept that the countersink in the wedge won't line up perfectly with the dimple. I don't know how much difference that few hundredths of an inch would make when machining the wedge with hand tools.
  3. Make the hole in the wedge slightly oblong (with... an end mill? Dremel tool?) or use progressively larger drill bits to enlarge the hole in the wedge until the forward edge of the hole in the wedge lines up with the forward edge of the hole in the skin, then machine countersink the wedge with the pilot against that forward edge. The hole at the "bottom" of the countersink will be oblong, but given that it's already knife edged, perhaps that doesn't matter.
  4. Cut a new wedge and start over. The problem with this is the two holes in the bottom skin that I've already drilled; I don't think I can drill precisely enough to hit the exact same hole a second time, leading to an oblong hole in the lower skin. Perhaps I can drill half the depth through the upper skin and half the depth through the lower skin and expect that any slight misalignment will be taken care of when I machine countersink the wedge.
  5. Take up gardening, where I can bury my mistakes.

I'm leaning in favor of option 2: countersink the off-center hole the way it is, but drill the rest of the holes the right way. But if the dimple won't fit the countersink, and I have to pivot to option 4, now I have to double-drill 18 holes instead of two, and that might lead me to more seriously consider option 5.
 
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