Rib flange-to-spar flange: When to drill, deburr (and maybe dimple)?

Bullseye · #1 09-30-2010, 06:17 AM

Hello everyone.

I was working on drilling my main ribs to the main and rear spar last night, and the instructions say "drill all of the rib to spar attach holes."

Then, they have you take everything apart, deburr, prime, and then rivet the ribs to the spars.

What should I do for the flange to flange holes? (Circled in green below, but there is one more on the ribs for the lower rear spar flange).

If I leave them as is now, I'll be match-drilling them with the skins later, but then I won't be able to deburr the holes (because the ribs are now riveted to the spars).

I could run a #40 bit through all of these holes and deburr before assembly. (I could also dimple the rear spar ones, since they will eventually be dimpled to accept the skin dimples.

Any thoughts?

Thanks in advance.

Auburntsts · #2 09-30-2010, 06:24 AM

On the RV-10 all of those #40 spar flange holes get drilled & countersunk a step before the fuel tank attach holes get countersunk.

airguy · #3 09-30-2010, 07:42 AM

On my 9A I matchdrilled and deburred the ribs/wing spars at your point, but waited on countersinking the wing spar flange until after I matchdrilled the skin to it later. That way your #40 bit will not wander in the prepunched skin hole trying to center in the countersunk spar flange. After matchdrilling the skin to the spar flanges, then countersink the spar flange, blow the chips out with compressed air, and deburr/dimple the skin.

You'll find that at about this point in the process the instructions from Vans start getting a little less specific on details, and you're expected to look forward in time and make some assumptions, and "just know" that such and such needs to be done. At one point in fuse instructions, you will find a statement to the effect of "There are a laundry list of small details that need to be completed before this next step, do those now" but no "laundry list" is given, you're just expected to "get it" by that point. Caution is advised, verify that brain is engaged before energizing the drill. I found it helpful to make a list of details written on a piece of paper, each time I got to a point where I had to leave something undone until it made sense to me later in time, I wrote that down on the list so it would not get forgotten. I periodically review that list to see what now makes sense to complete and what still needs to wait for some other component.

Bullseye · #4 09-30-2010, 07:47 AM

Quote:

Originally Posted by airguy

I matchdrilled and deburred the ribs/wing spars at your point, but waited on countersinking the wing spar flange until after I matchdrilled the skin to it later.

I think I like that approach.

I figured there were two philosophies. 1) Wait until the instructions tell you to matchdrill all of the layers, or 2) Since I know these will need to be drilled and deburred, do it now while it is accessible.

(The other thing I should remember is that with those layers tightly clamped, there really shouldn't be any big burrs.

Auburntsts · #5 09-30-2010, 07:53 AM

Just a data point as I just finished drilling my wing bottom skins and my top skins were riveted on months ago. My holes were CSK'd way prior to reaching this point, per the plans. There was absolutely no tendancy for the bit to wander as I match drilled the skins to the spar. Really, if you're running the drill long enough for that to happen or not close to holding the drill perpendicular to the hole, you need to re-evaluate your technique.

RV7ator · #6 09-30-2010, 07:55 AM

Ken Kruger just received an award for his work that makes the pre-punched kits so buildable.

Which is why I've found over four kits that you take the parts out of the crate, open all the holes to final size, then assemble as needed for fitting of fabbed components or drilling new holes to match a pre-punched. The specific holes you question can't be match drilled because there's only one cleco that could go through the flanges, so the rib pivots around it and the second holes will not be congruent, making your "matched" drilled hole oblong.

There's a lot of RV-6 artifacts in the -7 instructions that just don't make sense. A recent thread had to do with installing wings as an intermediate step in fuse construction that is totally unnecessary. I could go on, but raise a question in your mind or on VAF if your gut says to.

Dimpling should be the very last operation prior to any coatings or riveting. Dimples scratch. C'sinking should be last also because it leaves precious little hole diameter for centering assemblies for additional fit-up.

John Siebold

bkthomps · #7 09-30-2010, 07:59 AM

I think you're taking the need for deburring a little too seriously, those single holes on the rib not being deburred will not result in any catostrophic failures or structural integrity compromise, it's just good practice to debur anything you drill, I'm sure you will run into quite a bit more scenarios like this where deburing one last time before riveting will be out of the question