lots of rivets to drill out

[LukeS]

Hey Bearhawkers! It's been a while since I've posted anything. Those of you that know me, know that I'm a VA nurse and I've had to push my BH to the back burner while I finish my masters degree. During this time away from the project, I've been contemplating how to deal with the dreaded problem of drilling out over-driven rivets. In al of my enthusiasm to drive 2000 miles each way to pick up my bearhawk project from the previous owner, I didn't think to grab a set of calipers to check the rivet heads. As such I ended up inspecting them only by eye. Most of the heads looked very nice (likely squeezed), and I went through with the purchase. Unfortunately, most of the rivets are over-driven. This really sucks because one wing is already partially closed up. Just to research my options, I purchased a rivet removal tool from vintage trailer supply to help with the domed head rivets, and it worked great at keeping the drill straight and centered. What astonished me was how far I had to drill through the spar rivets to get them to relax enough that I could punch them out. I'm using the rivet gun to punch them out too, so it's not like I'm just tapping on it. I tried just using a drift and a hammer, but didn't have enough hands to hold something on the other side of the spar to back it up. This has me concerned about the flush rivets. Any words of wisdom would be appreciated.

[Bcone1381]

Luke, How close are the rivet heads to meeting specs? Are you judging them in accordance to the general specifications in AC 43.13 of ".5D x 1.5 D", or are you also applying the more detailed measurements found in the "Military Specifications of Riveting"? I really like "Mil Spec" tolerances. They are more forgiving.

http://www.vansaircraft.com/public/Specs.htm Look for table III about 1/2 way down.

Brooks Cone

[LukeS]

I was using the AC 43.13 general specs. because I assumed that's what the FAA inspector would require. But even using the mil spec guide you attached, the 5/32 rivet I just drilled out yesterday would still be .010 to short on the shop head.

[Glenn Patterson]

I can empathize with your situation. How grossly over driven are the rivets? If they are reasonably close then it may be worth a conversation with your inspector and have him take a look. If he would accept the work then that could save you a big pain. Drilling a good qty of the rivets out may do more harm than good. The spar rivets are heavy duty and really lock into the hole & the lamination layers. Had to drill out about 5 or 6 spar rivets that was enough.

Flush rivets drill out easy. The hard rivets have a dimple in the center which is a good point to start with a 1/16" pilot bit. The pilot can be moved to centerby working the bit if it is slightly off. Then slowly drill rivet size for size and the head will come off before touching the skin. We then took an automatic center punch and a couple shots with the spring loaded automatic punch pops the rivet out without any harm to skins. Once you get comfortable then you can skip the pilot as it is easy to see visual center & get the heads off cleanly. We drilled out lines of rivets to put strips in to close up the gaps between wing and the flaps & ailerons.

We had an inexpensive automatic center punch that we bought cheap & a better quality Starrett that was loaned to you. These are one of the most used tools in our shop. For precision work there is nothing better that the Lee Valley optical punch. A machinist showed one to me about 10 years ago & that has been an amazing tool to find absolute dead center.
http://www.leevalley.com/en/wood/pag...,42311&p=45502

Brooks military riveting information may assist in working with an inspector to get a pass. Anything to build a reasonable case to avoid a major rebuild. I think a rivet would almost have to be pounded really flat to have no strength. It may be worth a conversation with Barrows on the spar rivets. I think that they do not see much axial stress but clamp the laminations to the web & the stress would be more shear in the load sharing along the length of the spar. The spars are built like an 1890's railway bridge. We had a couple AME's look at the spars and they said they were the strongest they had ever seen in in a small airplane.

Glenn

[Deftone]

The lee valley punch is a beautiful looking tool....but at $45 is it really that much of an upgrade compared to a regular starrett punch?

[Chris In Milwaukee]

Where are you in Southern Wisconsin? Al Barger at Morey Airplane Company in Middleton (Madison) is a tech counselor I would trust with that question.

[LukeS]

Chris,
I'm in Monroe, WI. I work for the Madison VA. I've actually visit Morey field before.

[patrickh99]

I'll second what Brooks & Glenn said. Drilling out rivets usually leads to over-sized holes and more issues. Leave them if they are not grossly squashed.

[Glenn Patterson]

The Lee Valley Optical center punch will hit dead center every time. It is really good for accurate layout of parts. The Starrett works different and each type has its advantages. The optical is friendly to the eye as the top of the optical magnifier is dome shaped so it gathers light to make it very easy to see. Simply place the optical cross hairs on the center mark to be punched. Hold the brass base and drop in the steel punch. We drilled a 1/16in vent hole as the punch is a close fit and it takes a couple seconds for the air to get by it until it contacts the surface to be marked. The punch can take a good hit or two with a hammer to make a good deep center mark to start a drill especially in steel. I would not use it on aluminum sheet or use it very gentle. The automatic punches cannot set as deep as the LV center punch. The LV optical punch has had a good work out over the past 10 years and the point is still sharp as it was new.
The US price is $40

http://www.leevalley.com/US/wood/page.aspx?p=45502&cat=1,180,42311

Lee Valley makes quality tools in Canada. I made all the tool & die to form the wing ribs with a router base from Lee Valley.

http://bearhawkforums.com/forum/tools-technics-and-best-practices/233-routering-methods-for-bearhawk-jigs-dies

Glenn

[Deftone]

Thanks for the review Glenn, I think I will order one. Seems like it is worth the money!

[Bdflies]

I was intrigued. What could justify $40.00 for a center punch? I followed your link and read/looked at the punch. I ordered one. A fine tool is a thing of beauty. That looks to be a fine tool.

Bill

[Glenn Patterson]

It is a good purchase and it is a quality tool that will serve you well.
Glenn

[rv8bldr]

On a related (sort of) note, Leonard Lee, founder of Lee Valley Tools and a neighbor of mine, passed away on Wednesday. He will be sorely missed.


Sent from my SM-T350 using Tapatalk

[whee]

I too would measure them and leave them be it they weren't that bad. There are a few overdriven rivets on my wings and I'm not going to mess with them.

You guys mentioned having an inspector check them to so if they would let them pass. Does the DAR really care? Is he going to get out his calipers and start measuring rivets when he does his inspection? I really don't know. I've talked to the local DAR and a few builders that had him inspect their planes. Supposedly his inspection is equivalent to a preflight and most of his time is spent looking at the build log and asking questions.

[LukeS]

My concern is that the inspector will see an over driven rivet through an inspection hole that makes him lose faith in the rivets he can't see. I have thought of the tech counselor as an option, but even if a tech counselor says not to worry about it, I can't trust that the DAR will think the same. Personally, after pounding one of those rivets out, I'm not worried about the spar strength, but I'm no engineer.

[Glenn Patterson]

An EAA tech counselor is an option as they would be familiar with the the local DAR. It is is a shame to redo all the rivets if it is not necessary. In Canada we had to leave the bottom skin loose for inspection so the majority of the rivets are accessible. Our inspector looked at the rivets but did not do any gauging of the shop heads. If replacing the rivets that can be seen and within reach then the reality is the rest are what they are.

The concern is that you may be having a lot of angst where perhaps none exists. Lean on some experience as it may avoid a total redo. If it is not acceptable at this point then it is best to know as it is serious task if the plan is to redo every rivet. There is an expression that sometimes there is no greater fear than fear itself, You are second guessing someone that you do not know. I have worked with a wide range of inspectors in my life and have found them all to be reasonable. The inspectors that I worked with want it to be safe and often would offer the resolution to a sticky issue.

[LukeS]

Glenn,
Your advice all sounds reasonable. There is a member of my EAA chapter that was a tech counselor, and may still be. I'll reach out to him for some advice.

[davzLSA]

I recommend you buy a go/no go rivet gauge and check them with it before drilling them all out. Might save you come time, I built an RV4 so I feel your pain.

[LukeS]

I have gauges. That's how I identified the over-driven ones. I then double checked them with calipers just to be sure.

[davzLSA]

I hope you dont have to drill too many. It can be a real pain. good luck.

[DesertBearhawk]

Found This on the web....it was published in a news letter from EAA Chapter 724...

Riveting Tips From The People Who Make ’em


Tom Green has a desk full of interesting tidbits...so I wasn't surprised when he dug up a publication called "Alcoa Aluminum Rivets". One paragraph caught my eye:
"The standards to which driven rivets should conform are frequently uncertain. In addition to dimensions and perfection of shape, inspection is concerned with whether the driven head is coaxial with the shank (not "clinched") and whether there is excessive cracking of the heads. It has been determined that even badly cracked heads are satisfactory from the standpoint of static strength, fatigue strength and resistance to corrosion. (Poorly set and cracked) rivets were tested in tension to determine how well formed a head has to be in order to develop full strength. The tensile strengths of all the rivets were within five per cent of the strongest. The test indicated that minor deviations from the theoretically desired shape of head are not cause for concern or replacement. The second rivet that is driven in any one hole is likely to be more defective than the first, because the hole will be enlarged and the rivet will be more likely to buckle and form an imperfect head."
In another place, I found this: "Tests have shown that very small rivet heads are sufficient to develop the strength of the rivet shank, even when the rivets are subject to a straight tensile pull.... Where a large head is not needed for appearance... smaller sizes of driven heads should be used to decrease the required driving pressures."
In other words, rivets have a large margin of safety. Even under-set or cracked rivets provide sufficient strength. You will probably reduce that strength by drilling out a "less-than-perfect rivet" and replacing it.

[DRLPatrol]

Interesting, Thanks for posting that.

Doug