jlfernan

jlfernan

Well Known Member
A short while ago I match drilled the middle top skin to my QB 9A fuse. The holes in the fuselage were already drilled out to #40 and dimpled by the fellas from the Phillipines. I noticed after I was done that some of the holes in the fuse were slightly enlarged. I'm theorizing that because the flat skin is sitting over a dimple, and we all have noticed that dimpling a hole makse it even larger, the drill bit may not be going straight thru. My question is, since all the parts are precisely prepunched, do you really need to match drill or can you just drill the skin to the correct size and then dimple it?
 
If I get the question your asking, can you just drill out the parts without clekoing them together? My best guess is you can do anything you want. Problem is, the holes don't always line up real good and that last little bit of drilling allows the parts to be lined up. Our rivet holes are only close to precisely lined up.
 
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Right. Can I/should I drill the skin without clecoing it the fuse. Another reason for asking is that the skin got damaged in storage and I had to order another one. Now I fear enlarging the holes even more if I match drill again.
 
Jorge-
I did not match drill any of the top skin-longeron holes, for the reasons you mentioned. I only drilled the holes to full size then dimpled. I had 0.0 degrees of twist in the fuselage before riveted the top skins on and had 0.0 degrees after. All the rivets slid right into the holes on the first try and bucked nicely. In my opinion, this is one of those places where the CNC machine are so accurate that match drilling really serves no purpose that outweighs avoiding the problems you discovered. Messing up a longeron hole should probably be avoided at all cost. Good luck.
 
If the holes you refer to have been dimpled but not drilled, it would be best to run a drill through before assembly. The holes as supplied by Van's are punched rather than drilled. When punching holes in aluminum, the pierced hole is the same size as the punch for only about 20% of the sheet thickness from the side of entry. From that point the shearing of the material takes on a conical shape with the greatest diameter at the exit side of the sheet. Drilling not only gives a uniform cylinder to allow the rivet to expand into, it more importantly ensures that the full thickness of the sheet comes in contact with the rivet shank. This optimizes the performance of the rivet and helps prevent the joint from loosening. While you could probably get away without properly preparing the joint, or for that matter get by with only half of the rivet holes filled, why not maximize the strength?
Terry
 
jlfernan said:
My question is, since all the parts are precisely prepunched, do you really need to match drill or can you just drill the skin to the correct size and then dimple it?
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Terry-
Jorge is not suggesting that he not drill at all before dimpling. He's just asking if "match" drilling is necessary on these particular holes. It doesn't at all sound like he's trying to skip a step.
 
The holes in the fuselage were drilled and dimpled by the factory. The holes I'm referring to are in the new skin. I do plan on drilling to #40 and dimpling these, but what I'm asking, is it neccessary to match drill them to the bulkheads and skins which were already done on the fuse?
 
Jorge,

A local builder who has completed a 9A and is building a -7 gave up match drilling & just drills without clecoing together. Says they always fit. He showed us one hole, however that the factory punched in the wrong place, i.e., it was about 1 cm off from where it needed to be to line up with another hole. Noticed it before he drilled.

Actually, he goes one step farther. When 2 parts are identical or mirror images, such as L & R wing skins, he clecoes them together & drills both at once.
 
jlfernan said:
but what I'm asking, is it neccessary to match drill them to the bulkheads and skins which were already done on the fuse?
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No.

Any hole that has been already dimpled already has an I.D that is slightly bigger than a #40 drill.

One thing that can cause problems is if the factory builders didn't take much time in flutting the bulkhead flanges straight. This can cause you to still drill the edge of some holes because they are not quite aligned properly.

Just properly prepare the holes in the skin and rivet it on. If the holes in your
F-?07 bulkhead (baggage bulkhead) don't align well with the skin, you can still do a little adjusting with a flutting pliers. The F-?08 is a little more difficult to do anything with at this point.
 
Thanks guys for the resposes. Sent Vans an email just for giggles but haven't heard anything yet.
 
Just received a response from Ken S. He says it makes little difference. That the skins may be drilled off the fuselage.
 
Resurrecting this thread... Based on my limited experience with the empennage, and the discussion on this thread, it seems like match drilling skins on pre-punched kits is a waste of time. All of the slight misalignments I've seen thus far are due to errors on my part (cuved web, flanges not square, etc).

Anyone disagree? I'm not trying to be lazy--if there's any value to doing it, I will, but if there is no value, there's no reason to spend the time.
 
After building numerous kits and assisting others I can tell you that you should match drill the holes. The holes must be enlargened to the proper size.
 
Norman CYYJ said:
After building numerous kits and assisting others I can tell you that you should match drill the holes. The holes must be enlargened to the proper size.
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Agreed... holes definitely need to be drilled to the proper size. My question is whether it's necessary to cleco the skin to the assembly and drill the holes together.
 
After reading this thread when it first started I tried drilling holes to size on some parts without matching (clecoing) parts together. Including the aft upper fuselage skin that's left off on the QB fuselage. When I test-fit that skin, it lined up perfectly. I'll still match drill on small assemblies, but on the big parts I don't bother. Just drill to size, deburr, dimple as required, done.
 
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