After drilling the horizontal stabilizer to A4 size, I disassembled to begin deburring and corrosion control. When I removed the skins and starting breaking down the skeleton, I saw where I had damaged 3 of the 4 rear ribs during the drilling. I don't think these ribs would pass inspection (certainly not mine!) and I'm ordering replacement ribs this week before proceeding on this assembly. Wondering if anyone else has had this issue?

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Comment by Lawrence Van Egmond on May 22, 2012 at 12:50am

It is a common problem and it helps if you use a high speed drill and once through top skin use very light pressure so the rib is not pushed down and let the bit do the work. Cleco  as you go and it will help hold everything in place.

Comment by David A. Judkins on May 17, 2012 at 9:56pm
Good comments! I like the idea about the rib molds.
Comment by Phil Smith on May 15, 2012 at 9:53am

OK Kids,


You have a problem much like I experienced - I think. That is the ribs flexing while you drill causing an "oblong" or miss-formed hole.  Simple fix is to FAB some inserts that closely mirror the "interior of the rib" from wood - plywood or OSB works well - that fit inside the ribs for support during drilling. Also might think ahead and plan to do this on most of the rest of the "rib" structures in the wings, flaperons and slats etc. You just put the rib on the wood and trace around the outside then cut a little smaller. You don't have to have it exact just snug where you want the supprort. Once you get one then you copy the rest.  Not the most fun but works well.  I found that I had to be very carefull in these areas.

Also sharp drill bits are a neccesity.  If you haven't dicovered "The Drill Doctor" sharpening machine yet - look it up it saves a lot of grief as you drill along. I don't remember the model I have - but is the mid range model with the ability to put a "split point" on the drill bits. Read the instructions and get the set-up right and you'll love it - probably end up sharpening all your drill bits.  Another tip, when I sharpen bits I finish off the drill bit by marking the "cutting edge" with red marker so I know where I am - the marker wears off immediately when you drill but you know what bits are freshley sharpened and the ones you have used..

Still Grinnin !!!!


Comment by David A. Judkins on May 13, 2012 at 11:04pm
Yes, I think I understand. I'll try that next weekend when I resume work. Thanks again!
Comment by Dan Kellogg on May 13, 2012 at 10:03pm
Technically, you could just put it in the area of the double drilled holes, but I always prefer to err on the side of caution. I would add the doubler so that it is long enough to pick up at least two of the adjacent holes, including proper edge distance (10mm) past the last hole. This adds additional reinforcing and also holds the angle in place by using the two good holes as a guide to drill the angle. After you drill the two good holes you can then put the skin back on to use as a guide to drill the bad holes. Hold the angle in place with clecos using the two holes that were drilled previously. On second thought, it will be difficult to shape the ell around the fluted section on the top chord. You could just make it long enough to catch the hole adjacent to the double drilled one. Another solution is to add the doubler to the top chord of the rib and notch the edge that is facing down (like you do for the slat brackets with vee notches and a radius at the end of the vee) to conform to the top chord shape. You would then have to rivet the doubler to the side of the rib with the same number and size of the rivets that are in the skin, connecting it to the rib. (did that make sense?)
Comment by David A. Judkins on May 13, 2012 at 9:28pm
Thanks, guys, for the comments. Should the angle cover the area around the damage only or should it extended out to help distribute the load?
Comment by Dan Kellogg on May 13, 2012 at 7:18pm
Agreed. You just add a "doubler" made from standard angle. It will distribute the load across the rib and you just need to re-drill the holes. No need to order new ribs.
Comment by Geoff Klestadt on May 13, 2012 at 3:16pm

Don't worry, did the same. Easily fixed with some L angle. Give Caleb a call.

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