setting rivets 1

[dukmn]

What causes rivets to bend off-axis rather than crushing straight down along the long axis of the rivet when you try to set them?

I am setting some 5/32 aluminum rivets (AN470AD-5-8)to fasten a patch piece onto the hull of my boat. If I use a long enough rivet to give 1/4" protrusion they don't always set right. Some try to bend over rather than crush straight down. Going to a 1/8" shorter rivet solves the problem, but now the rivet head isn't thick enough (I think).

I've got a rivet gun with the appropriate rivet set. I can't blame the person on the buck bar because my wife is helping me.

The hull is thickness is 0.100 and the patch piece is 0.125. The rivet length is 0.50, leaving a 0.275 stub poking through the hull of the boat to set the buck bar on.

I drilled the holes through the patch piece on a drill press, so they are square. I drilled the holes through the hull by hand, so some aren't perfectly sqaure to plane of the hull.

So far as I can tell, a 5/32 rivet should be ~0.25 longer than the grip to get a good head. Mine are ~0.275 longer.
Some set up perfect, but many lean over.

What am I doing wrong? Thanks

 

[Sparweb]

Given that this is a patch in a boat hull, and not an aircraft, it may not be too important to have perfect rivets. In any event, properly set rivets look much nicer.

The problem is not obvious. Check again the settings on the rivet gun. The driving should take only a few solid whacks to fully drive the rivets. It only takes a few seconds.

I agree with your length measurements. I suppose your boat is aluminum. Is the patch going on the outside or the inside? You're using a sealant, too, I expect. Are you driving the rivets "wet"? That makes them slippery. You stated that the rivets are "AN470AD5". I take it that they have the protruding head? (The flush head types are harder to drive straight.)

Try practicing with a test piece clamped in the vise. Your partner can buck and you drive, like normal. I take no responsibility for any discussion that ensues from directly observing each other's techniques.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[dukmn]

Thank you.

The patch is on the outside, the rivets have a button head, and I am using a sealant.

Your counsel to practice on a test piece was great. I set up a test piece in a vise and experimented a little. One thing I noticed was that if the buck bar was not held plumb to the rivet that it would cause the rivet to angle off center.

I am now working on a tactful way to explain this to my partner.

Thank God this is not airplane. The patch piece will be structurally sound and water tight, but I wouldn't care to bet my life on it.

 

[Sparweb]

"I am now working on a tactful way to explain this to my partner."

I haven't mastered that technique, either.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[Stache]

Driving rivets is an art and takes practice lots of it. I have about 200 pds of bucking bars to select from depending on the rivet and location.

It is very important to select a heavy bucking bar for 5/32 rivets and hold it straight to make the correct shop head. For 5/32 rivets I us a 4X rivet gun and 90 lbs shop air. Holding the rivet gun straight will insure all of the force is transferred to the bucking bar. I also use me middle finger to operate the rivet gun. This aids to hold the gun straight.

It took me several years of practice to make most of the rivets look good I shot.

Stache

 

[dukmn]

I have a 3X gun, and am running it at 90 psi. I started out with the air adjustment throttled down on the rivet gun, and then started opening it up as I hammered away on some test pieces. I am guessing that it takes 1-2s to set a rivet. My gun is rated at 2160 blows per minute so this would mean ~50-70 blows to set a rivet. Do I need to adjust up for even more force per blow and less blows overall?

Positioning of the buck bar appears to be the key. I set up a practice piece in the vise, and my wife and I kept practicing until we began to get a feel for it. The shop heads we produce now are much better than when we started. Based upon my limited experience setting rivets I strongly agree that this is an art that takes lots of practice.

Thanks to all of you for your valuable assistance.

 

[Stache]

When I first started out I used my wife on the rivet gun and I bucked. Not a good idea, but we worked out the dents.

I use a heavy bar after getting the first one the way I wanted it and rest the heal of the bar on that shop head and the rest fell into place. Another trick is to place some masking tape on the rivet set this keeps the set from moving around the rivet head when driving. On flush head rivets the masking tape leaves on marks on the skin. However make sure you over countersink the hole just a little and it will swell flush. This may take several attempts to master, but on bare skin it sure look nice.

One note about bucking bars make sure they are smooth and polished. Having a nick will damage the shop head. I used a polishing wheel to keep them smooth like Scotchbrite.

Stache

 

[Sparweb]

I was once accused of poor technique bucking rivets, having left a smiley face on most of them. Only after experimenting for half an hour and fretting about what I was doing wrong, did I notice that there was a ridge inside the set of the gun. How it got there, nobody knows.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[edmeister]

A classic reason for 'dumping' rivets is that the hole is too large (loose). Sometime after drilling out rivets - the hole will be too big. Are you replacing fasteners or installing new fasteners? For 5/32 rivets (aircraft) - a #21 size drill bit is required. Should the rivet be 'tipped' in the hole - And either the rivet gun - or the bar not be correctly placed on the rivet - it will dump. The rivet should be very snug in its hole.
A trick that you can attempt is to obtain a piece of 1/8 or 3/16 thick rubber (1/2" x 1/2" size) and punch a hole in it just under the diameter of the rivet. Place it over the rivet tail. Not only will this prevent 'tipping' of the rivet - but also assist in preventing the rivet from forming between the skins.
Happy riveting ... & say Hi to the Mrs. !

 

[dukmn]

Edmeister: you nailed a couple of my defects as a riveter.

I am attaching some patch pieces to the hull of my boat where the trailer rollers have worn into the hull over time. I was afraid that eventually the rollers would wear all the way through the hull, so I added the patch pieces as a sacrificial shield to the hull. All the rivets have to do is be water tight and hold the patch piece in place. I used double rows of rivets on 1" centers. Each row is 1/2" apart and the rows are offset from each other. Even if one or two rivets screw up, the patch piece can't go anywhere. I used a marine sealant (Bostik 920) when we attached the patch pieces. So far it is water tight. We'll probably have to wait 10-20 years to see just how good of a job we did.

A few of the holes for new rivets weren't drilled plumb, and the buck bar wasn't placed square to the rivet. These rivets laid over the first time we did them. As you point out, alignment of the gun and buck bar with the rivet is everything.

Some of the holes for replacing old rivets got egged out a little because I didn't get centered squarely on the rivet when I drilled it out. On the holes that were badly out of round I made little patch washers out of 0.125" material, placed them over the rivet tail, and used longer rivets. This solved the tipping problem, but I'm wondering how structurally sound it is. The boat skin is sandwiched between the patch piece on the outside and my washer on the inside. I'm guessing the rivet didn't fill the hole in the boat skin. Is the only proper cure for this problem to drill out the hole until it is round and then go with an oversize rivet?

Thanks for the tip on the rubber washer.

 

[bluesincenew]

Hints for next time:

In .225 material a 3/16 rivet would be recommended. Typical aircraft skins and attached structures running .100+ use 3/16 rivet.

For standard 3/16, I have always used a #10 bit. 5/32, I use #20.

For selecting rivet length, add 1.5 diameter to material thickness. So for -5 that would be .234 exposed for upset head.
Upset head dimensions:
5/32-- dia .203 .281 / height .063 .094
3/16-- dia .250 .344 / height .078 .125

For basic information try the Standard Aircraft Handbook
ISBN 0-8308-8634-7 (eBay ~$6)

Practice makes perfect.

 

[dukmn]

Thank you once again. All of you. My boat still floats inspite of all my various screwups as I attempted to master the art of riveting. Generous application of Bostik 920 marine grade sealant helped to compensate for my amateurish mistakes.

I cruised over to Amazon, and found this book:

Standard Aircraft Handbook for Mechanics and Technicians
by Larry Reithmaier

Is this the book?

 

[WKTaylor]

dukman...

Lost of good rivet practices... and more structural maintenance info... is located in AC43.13-2 Chg 1 at the following FAA website.

See chapter 4 for sheet metal work; including riveting

http://www.airweb.faa.gov/Regulator...99C827DB9BAAC81B86256B4500596C4E?OpenDocument

Stache...

Caution: it is generally NOT good practice to over-countersink and "let the rivet fill the hole". What happens it that the top of the rivet-head MUST bare against the gun-anvil to acutally transfer riveting energy to collapse the shank [each rivet installation is a "mini-forging operation]. If the head is below flush, then the rivet will BACK-OUT of the hole/countersink slightly to establish this contact with the gun-anvil. If You section [metallurgically cut-across] these joints, You will find shanking and voids that have a high potential to trap moisture and develop premature rivet "looseness" or head failure.

Typical good practice is to have the head almost flush to very slightly high (-0.0005 to +0.0050). This allows the rivet gun anvil to bare against the rivet head for driving with the rivet set tight in the hole/countersink for the driving operation... and will also eliminate/minimize skin damage around the rivet head.

NOTE: MS20426 Flush Tension head rivets are actually intended to be driven slightly high, then milled flush with the skin, resulting in very high smoothness [if done correctly].

NOTE: NAS1097 rivets and the proprietary crown-flush rivets deliberatly place a small dome ["crown"] on the top of the rivet head so that it protruds above flush and will almost always contact the gun-anvil... even in slightly deep countersinks [crown & dome feature have about 0.007 protrusion above the nominal "plane" formed by the edge of the flush head]. This feature allows for more uniform driving and much greater flush-riveting consistency [statistically significant].


Regards, Wil Taylor

 

[karlbamforth]

I realise this is a bit late but might be useful next time.

Newcomers to rivetting often think that they have to lean hard on the bucking bar or gun. This can cause problems especially with the bucking bar. All that is required is to control the bar, holding it square to the rivet and prevent it "walking" around. Similarly with the gun hold it square, apply slight pressure to prevent it bouncing on the rivet, then let it do the work.

Karl.