Flaperon Counterweight Drilling Technique

[JMS1198]

Hi guys, I’ve been working through the fluting of the ribs and drilling of the counterweight for the flaperons. A military sheet metal guy gave me this technique that I want to share with everyone (I’ve seen many different techniques to include marking the holes and drilling on a drill press). This works well and makes clean holes without elongating the skin holes. Use a drill bushing #30, a drill bushing housing, 2.75 inch number 30 drill bit and two layers of painters tape to protect the skin. I used oil on the drill bit and also a slow speed to drill the holes. Have a few drill bits at the ready, the stainless dulls the bits fairly quickly.

[BobbyLucas]

I also found that starting with a smaller drill bit, say #40, and then finishing with the #30 produced much cleaner holes in the skin. Starting with a small spotting drill might help as well as those shouldn't wander. I seem to remember I also used a spring-loaded center punch to help the bit stay in one place.

[JMS1198]

The drill bushing and housing allowed me to start with the 30 bit, the stainless eats bits quickly…the technique made very clean holes.

[RFSchaller]

Here’s another tip. Start drilling with cheap Harbor Freight drill bits until you work your way up to the final size which is drilled by the expensive aircraft bit. No sense burning up expensive drill bits.

[BryanStearns]

I’ll be doing my counterweights shortly, so this tip’s timely - thanks!

I’ve found a few sources for #30 slip-fit drill bushings (Yard Store, Aircraft Tool Supply), but I haven’t been able to find a housing that looks like yours — all I’ve found are the plastic egg-cup style, which looks like it has three “legs” around its round base that might not sit squarely on the curved skin. Any suggestions?

[Marc Bourget]

For the less experienced, compared to drilling steel, the drilling stainless approach is slower drill speed with more pressure.

Stainless work hardens fast and the idea is to increase the pressure to keep cutting "under" the last pass - hopefully encountering fresh, "un-hardened" material each rotation.

My good reference, a Boeing guide, is at the office but, as always, practice on some scrap.

The drill bit you "extend" may be your own!

[thiggins]

I used my drill press with drill blocks.
Worked just fine.

[ravenstar]

This is most timely as I just started drilling these today, thanks! I'm finding that drilling leaves a significant burr on the inside of the tube, unfortunately. I can file this down on the holes near the ends, but does anyone have advice for deburring the other 11 holes in the tube? I found a thread from 18 years ago (!) suggesting just shoving another tube through the pipe. Is that still the best advice?

[SARLDO]

Originally Posted by ravenstar

This is most timely as I just started drilling these today, thanks! I'm finding that drilling leaves a significant burr on the inside of the tube, unfortunately. I can file this down on the holes near the ends, but does anyone have advice for deburring the other 11 holes in the tube? I found a thread from 18 years ago (!) suggesting just shoving another tube through the pipe. Is that still the best advice?

I just went through this. I attached a file (taped) to the end of a broom handle and ran it up and down the inside of the tube. No visible burrs after.
YMMV

[BillL]

Originally Posted by JMS1198

Hi guys, I’ve been working through the fluting of the ribs and drilling of the counterweight for the flaperons. A military sheet metal guy gave me this technique that I want to share with everyone (I’ve seen many different techniques to include marking the holes and drilling on a drill press). This works well and makes clean holes without elongating the skin holes. Use a drill bushing #30, a drill bushing housing, 2.75 inch number 30 drill bit and two layers of painters tape to protect the skin. I used oil on the drill bit and also a slow speed to drill the holes. Have a few drill bits at the ready, the stainless dulls the bits fairly quickly.

Joe, thanks for the tip, but on a sidebar - can you say what the brand/part number of that clever drill guide in the photo?

Thanks!!