J

JHines

Well Known Member
Could someone please explain the secret to "thin bucking bar" success for places like the skin-to-rib joints at airfoil trailing edges?

I've heard of various "thin" items (hatchets, chisels, ground-down bucking bars, crowbars, etc.) being used two ways:

1) Against the shop head the way you would use a regular bucking bar; and

2) as an "extension rivet set" laid across another bar and cantilevered over the shop head, with the gun applied to the bar's shank (i.e. backriveting).

I can't get either method to work worth a darn - seems like all the energy gets dissipated and the rivet just won't form up before it work hardens.

Using a 3X gun on AD4 rivets - tried all kinds of air pressure settings
 
Weight is the secret

Jonathan the secret of thin bucking bar is the mass of the bar. That's why some thin end bars have such a weird shape. The end could be thin but the center of the weight has to be very close to the rivet. The closer the better. The heavier the better. Somebody here inventive enough posted his self made thin bucking bars a while ago.
 
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Jonathan,

FWIW, I didn't have much luck either with the thin bucking bar techniques that you describe. What did work for me for most things was to go down to the local salvage yard and buy a piece of flat steel stock to use as a bucking bar. Mine started life as a piece of some sort of farm machinery, is about 3/8 inch thick and 2.5 inches by 8 inches. Looks like a trapezoid when looking down the long direction at the end of the piece (I think it was some sort of cutting implement). I ended up grinding some funny shapes on the corners to allow me to get into tight spots. The main thing is that it is massive enough to really act as a bucking bar even if you are only using the corner.

greg
 
are you really trying to do this with ad4 rivets... i had good success with indirect backriveting the tightest points of trailing edges with ad3 rivets with the line pressure turned up to about 50 psi. i do not think that i could have set ad4 rivets the same way; they require more energy than i could deliver.
 
I'm using a piece of tungsten I got on eBay for a couple bucks. It measures 1/2" wide by 1/4" thick and is 6" long. Its worked quite well in those tight clearance areas so far on those -3 rivets.
 
mass power momentum

The bars mass can be reduced provided it bounces on the rivet square. A little momentum as the bar hits the rivet can do the trick. I have taped a light bar to my finger with some rolled up paper towel on the other side of my finger for padding. Let it bounce and listen for the bar hitting with the gun. You will hear if the gun is hitting twice before the bar is back on. Consider going with a slightly short rivet and not smash it per text. So long as it fill the hole you should be O.K.

Andrew
-4 started and sold
dreaming again
 
Try a different gun...

The bucking bars mass is critical to getting the rivet to set, but don't forget that's only 1/2 of the equation. The gun is the other half.

I've been using a 4x Long Stroke gun for years now. It hits much slower and harder than the 3x. I simply dial the pressure down to around 50 psi for the -3 rivets and its just goes bang - bang - bang - bang. Nice and controlled.

Give a 4x gun a try in these situations.
 
Jonathan,

Here is a picture and text of what I was talking about on the phone.

From my web site

Here is a picture of how I was able to squeeze the last rivet on the end aileron ribs. I used the handle of a small pair of needle nose pliers to "open" the rib and then used my Avery's no-hole yoke to reach the rivet. I had to partially squeeze the rivet, push it down with a center punch and then finish squeezing it the rest of the way. (6/6/04)
Click to expand...
 
N941WR said:
Jonathan,

Here is a picture and text of what I was talking about on the phone.

From my web site
Click to expand...

Funny you should post that - I used EXACTLY that technique just a couple hours ago on the end ribs for my right aileron. Works like a charm, just don't set it so far that you can push the rivet back down into position before setting it completely.
 
OR YOU COULD TRY THESE.........
KNIPEX-1.jpg

THE SMALL (7.5") KNIPEX WORK GREAT FOR -3 426 RIVETS. YOU CAN EVEN GRIND THE TOP OF THE JAW DOWN FOR MORE CLEARANCE.........:)
 
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