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  #1  
Old 09-15-2018, 09:36 AM
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Strikefinder Strikefinder is offline
 
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Default Proud rivet shaving?

Hey again all,

For those keeping track, I started installing the platenuts on my spar over the past few weeks, and I'm just about done with this step. Though most of them came out pretty well, there are a handful of rivets (I'd guess maybe ten) that, for whatever reason, are just slightly proud of flush. I've been tweaking my technique as I've gone on and I think I've improved as this step has gone along, but now I'm trying to figure out if I should do anything about the proud rivets.

To be clear, they are barely raised--none are grossly out of whack. I don't think that it's worth the risk or hassle to drill any out, but I've been doing a lot of reading about rivet shaving using a high-speed countersink cage, a shaving bit, and a die grinder (none of which I currently own). I know I'd need to practice a whole bunch on scrap before even attempting this on the spar.

So here's my question: is this worth the effort? This whole area will be covered by skins, so I'm not concerned about aesthetics, just want to know if there's a structural problem with a handful of these being slightly raised.

I tend to think it's not worth bothering with and should just let it go, but I don't want to risk some sort of fatigue cracking. Should I work to make this perfect, or just move on?
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  #2  
Old 09-15-2018, 10:13 AM
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BoilermakerRV BoilermakerRV is offline
 
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Default Build on!

Structurally the proud rivet would be slightly lower strength in tension (less of the head engaged in the countersink). However, I think the main load in a nutplate is shear which would be identical or maybe even slightly higher (more of the shank engaged in the spar flange). Seems the risk here is much greater than the potential reward.

Just thinking "out loud".
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  #3  
Old 09-15-2018, 01:08 PM
Robert Anglin Robert Anglin is offline
 
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Default Sure.

This one is up too you. Shaving flush rivet heads is and has been done. We have been know, that if we catch a finger nail on one to shave it as long as it does not stick up to far and that is the judgment you have to make. There are costly rivet shaving tools that are used in the big aircraft plants. For the one or tow that just stick up enough to make you want too shave them, we have been know to carefully touch them up with a Drimmal tool.
Hope this helps, Yours, R.E.A. III # 80888
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  #4  
Old 09-15-2018, 01:41 PM
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Default Drill

I drill them unless it's a major pain to buck. Get skilled at drilling rivers. Some day it will come in very useful.
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  #5  
Old 09-15-2018, 02:01 PM
greghughespdx greghughespdx is offline
 
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Photos of examples?

Typically rivets in nutplates are non-structural in nature - they're just there to keep them in place when the bolt is not tightened into the fastener. Once the relevant bolt or screw is tightened down, they're just basically another nut from a structural perspective, and the riveted "ears" are not contributing to the structural strength.

If they're not interfering with the skins, and if they're not holding/fastening anything other than the nutplate, I'd at least consider leaving them alone rather than drilling them out.
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  #6  
Old 09-15-2018, 02:20 PM
PilotjohnS PilotjohnS is offline
 
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Default Old airplanes

Working on old airplanes, I have seen where the platenut rivets that stuck above the surface wore into the cover. And since the rivets do less good once the screw is installed, I try and make the platenut rivets flush or a little below. The old airplanes were 10000+ Hours airliners. Doubt a proud platenut rivet would have any effect on our homebuilts.
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  #7  
Old 09-15-2018, 08:06 PM
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Quote:
Originally Posted by wirejock View Post
I drill them unless it's a major pain to buck. Get skilled at drilling rivers. Some day it will come in very useful.
In principle, I agree with you...and though my rivet drilling skills are not yet perfect, I'm generally more than willing to sacrifice the part if drilling it out and starting over again doesn't work out.

My issue here is that the part in question costs $1700 plus shipping per. If this were a flap rib, I'd do it over again without hesitation...but if my skill isn't up to par, I'd hate to scrap a whole wing spar in the process of "learning".
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  #8  
Old 09-15-2018, 08:20 PM
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Quote:
Originally Posted by greghughespdx View Post
Photos of examples?
This is pretty representative. The feeler gauge puts this at 0.003" proud.

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  #9  
Old 09-15-2018, 08:28 PM
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Quote:
Originally Posted by PilotjohnS View Post
Working on old airplanes, I have seen where the platenut rivets that stuck above the surface wore into the cover. And since the rivets do less good once the screw is installed, I try and make the platenut rivets flush or a little below. The old airplanes were 10000+ Hours airliners. Doubt a proud platenut rivet would have any effect on our homebuilts.
I've been very tentative about over-countersinking because of the hole diameter problems people have had in their spars, and though I've gained confidence as the platenuts went in, I think I started out reluctant to go quite far enough for fear of overdoing it.

I'm not too worried about the platenuts coming loose, and from what I gather, if I make the #8 holes the "correct" size per Vans advice, the tank skins will sit just slightly above the surface when screwed in, so I expect and wear to the underside of the skins to be limited. That said, I've never built an airplane before, so I tend to worry about things I don't know.

Unless the discussion changes direction, I think I'm going to leave them alone, if only for now. I'll probably amass the tools to shave the rivets per other posts and play with it extensively on scrap before making a decision to try it or not on the spar, but my gut is that if I decide to leave well enough alone that I won't come careening out of the sky down the road (for this reason, anyhow).
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  #10  
Old 09-15-2018, 08:49 PM
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In case anybody reads this down the road, the MIL SPEC (MIL-R-47196A) specifies that "Unless otherwise specified on the engineering drawing or specification, flushness limits shall be 0.010 inch above to 0.005 inch below the material surface." It goes on to say that if you want to shave it, the limit would be 0.006" proud.

If I understand this correctly, I'm still "within spec" and could "legally" shave this rivet and still stay within spec (providing I don't FUBAR it). I feel more confident having read this that, imperfect as they may be, they are "acceptable" per the standard.
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