rivet set height issue

jpmfgman · #1 11-15-2015, 08:05 AM

I bought a mid build RV7 project with in general very good quality workmanship. I do have a concern with some of the rivets being over set on the following parts. F-773 aft side skin to F-768B and F768C upper and lower fuselage J stiffeners. The aft and rear top skins are not in place yet so I have good access to these questionable rivets. The driven head height thickness tolerance for the called for AN426AD3-3.5 is .038" min to .050" max. It's difficult to get an exact measurement but using a depth mic I feel that some of the driven heads are less then the .038, somewhere in the .025 to .030 range. The diameters are in the .170" range which is well above the .122 min diameter range. The large .170 diameter confirms the short overset heights. Specs are from http://vansaircraft.com/public/Specs.htm

My plan was to drill out and replace these overset rivets. A lot of work but doable. Even after drilling thru the rivet center with an undersize .080" dia drill and breaking off the flush head off, the hole diameters are still round and .120" max dia. So well above the max .103 diameter for the 3/32" rivet. I drilled two and have the same hole diameters. I feel my rivet removal drilling on these two holes was good and did not grow the holes to that .120 dia.

I ran a #30 reamer thru with my fingers and set a 1/8" rivet in one of the holes. The -4 rivet is as flush on the skin and the set head looks great.

Having said all that does this seem like an acceptable process to remedy my concerns about the overset rivets? Has anyone faced the same issues and how did you go about the fix?

I will run this by Van's also but appreciate any opinions.

RVDan · #2 11-15-2015, 08:25 AM

Something sounds wrong here. If a -4 rivet fits the existing dimple well, then you probably dimpled the holes with a -4 set. That might explain the oversized holes and resulting short rivets.

Typically when fixing an oversize hole you would use a NAS1097 rivet which has the head one size under the shank size when compared to AN426 rivets.

So if the AN426-4 rivets fit the dimples and aren't distorting the sheets when driving them, it will be the best solution.

ShortSnorter · #3 11-15-2015, 08:31 AM

I'm not an expert by any stretch of the imagination, but the advice I've always received is that a few over driven rivets here and there is not a big deal. The specs are standards. If every spec had to be met on every rivet, then there wouldn't be that many airplanes flying (RV or Certified).

I'm sure you'll get many more detailed responses than I've offered, but again, I wouldn't sweat it.

Edit: After reading the other replies, I realize I misread the OP's question. Gil's response makes the most sense except for the fact that the -4 shouldn't fit the dimple if it was an oops rivet

wirejock · #4 11-15-2015, 09:57 AM

Isn't the .103" dimension for the drilled hole? The holes stretch when dimpled. I could be wrong. Probably am. Maybe a call to Vans is in order.

az_gila · #5 11-15-2015, 11:14 AM

Quote:

Originally Posted by wirejock

Isn't the .103" dimension for the drilled hole? The holes stretch when dimpled. I could be wrong. Probably am. Maybe a call to Vans is in order.

No, it's for the actual hole.

A #40 drill is 0.098 and a #41 is 0.096. Dimpling will expand the effective hole but still should be below the 0.103 dimension.

Another possibility is that the offending holes were already deemed faulty and had been replaced by NAS1097 "oops" rivets. If the original builder used the same dash number for the length he would have ended up with what looks like overdriven rivets. Since the "oops" rivets are 1/8 diameter they need to be longer than the 3/32 rivet they are replacing to get the preferred 1.5D/0.5D driven head dimensions, which is now based on D=0.125.

maniago · #6 11-15-2015, 12:42 PM

I agree with the comment that you must have -4 dimples inthe skin. NAS1097 -4s would still sit below the surface like 426-3s. Either way if 426-4s fit in the dimples, then 426-4s are your solution. If you get some that sit proud, then use a rivet shaver once theyre in - that'll effectively give you a NAS-4 rivet and you'll still have the smooth surface we all desire.....

All that noted, there is alot to be said about not messing with a marginal set rivet. Its gotta be really bad for me to take it out and I'm a perfectionist at heart. You can do a boat load more damage by dicking with rivets that are probably good enough, especially if there are others around it that are "in spec". If you doubt it, do some tests with over driven rivets and see just how much you can pull stuff apart - you'll find its stupid hard in the shear plane, and pretty hard in tension. I worry more about healed over or bent shop ends (which I do take out) than marginally over driven ones.

jpmfgman · #7 11-15-2015, 12:44 PM

Thanks for the replies. Below are pictures of 3 holes and one of the rivets (front and back view) that came from the far right hole in the pic. I have drilled 3 in a row and they all look like this. It seems that Gil may be exactly correct and the original builder used 1/8" oops rivets here. I have never used this type of rivet only read about them so need to get educated on them. The ID of the hole in the rivet is about .101 and the OD is about .136 best I can measure so it seems to be a 1/8" rivet that has been expanded in the setting process.

jpmfgman · #8 11-15-2015, 12:56 PM

2nd try with the pics.

Thanks for the replies. Below are pictures of 3 holes and one of the rivets (front and back view) that came from the far right hole in the pic. I have drilled 3 in a row and they all look like this. It seems that Gil may be exactly correct and the original builder used 1/8" oops rivets here. I have never used this type of rivet only read about them so need to get educated on them. The ID of the hole in the rivet is about .101 and the OD is about .136 best I can measure so it seems to be a 1/8" rivet that has been expanded in the setting process.

maniago · #9 11-15-2015, 12:58 PM

yeah looks like NAS or a shaved head.

FWIW I exclusively use NAS 1097-3s to set all my nut plates as you can countersink down to .025 metal and the heads will be flush and no knife holes, where as 426-3s I'm not comfortable countersinking less than .040 material.....and forget dimpling for nutplate-anchor holes....

jpmfgman · #10 11-15-2015, 01:47 PM

pictured are the rivets in question with a .032 feeler gauge that pretty much matches the height of the shop head. These rivets are 1/8" so they should be in the .050 to .070" height range. You can see the row of rivets so it's not just one or two here or there.