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Replacing rivets with bolts

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grs-pms(at)comcast.net
Guest

Posted: Mon Sep 25, 2006 2:31 pm Post subject: Replacing rivets with bolts

Bob:

  

 This question came up a few months ago, and I  posted some comments at that time.  You are right, the bolt is  substantially stronger than the AD rivet of the same diameter.  Your wing  won't be any stronger though, since most of the fasteners will still be rivets  which will fail before the bolt can really do its share.

  

 The issue to consider is the fatigue resistance of  the spar.  A driven or squeezed rivet expands to fill its hole and  puts the material surrounding the hole in compression, which tends to keep  fatigue cracks from starting.  An AN bolt in a drilled hole doesn't have  the same effect.  Under normal operating stresses the material surrounding  the bolt feels as though there is nothing in the hole, and it experiences  fluctuating tensile stress.  Fluctuating tensile stress tends to start  fatigue cracks.  

  

 To keep the fatigue quality equivalent to a rivet,  drill the hole slightly undersize and ream it to the actual (measured)  diameter of the bolt.  Bolts in the standard AN bolt series (AN3, AN4 etc)  have a fairly wide tolerance on diameter, so the nominal diameter is  misleading. What you want is a fit which is  close (or tight) enough that the bolt has to be tapped into place, not just  pushed in with the fingers.  Reaming also makes sure that the hole is  really round, so the bolt is in contact with all the material around  the hole.

  

 For the few bolts involved it might be a good move  to invest in close tolerance bolts in the AN173 series.  They have the same  strength as AN3 etc, but the diameter is closely controlled.

  

 I have taken my own advice on this issue, using  close tolerance bolts in reamed holes on my CH601 HD spars, where the  factory-built spars needed additional fasteners.

  

 George

  

  

  

  zenith-list(at)matronics.com (zenith-list(at)matronics.com) 

 [quote]   Sent: Monday, September 25, 2006 12:17    PM

   Subject: Places hard to    rivet

   



   Members,

        Has anyone ever    thought of just using a small (Same shaft diameter as the rivet) bolt, two    washers and a lock nut in place of the rivet.  I don't think there are    very many places where this problem will crop up therefore not much extra    weight will be added and the nut and bolt will be just as strong if not    stronger than the rivet.

    

   Bob Stone, Harker Heights, Tx

   ZodiacXL  DO NOT ARCHIVE

 	  Quote: 	
		  

	
   

      Date:    9/22/2006

[b]

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J2j3h4(at)aol.com
Guest

Posted: Mon Sep 25, 2006 3:48 pm Post subject: Replacing rivets with bolts

How about drilling and tapping the hole using the recommended tap drill  size?  When you tighten up the nut on the steel bolt it will deform the  threads in the aluminum to give you a very tight fit.  Radical, I know, so  feel free to disagree.  Also, don't call me if your wings fall off.

  

 Jim Hasper

  

  

 In a message dated 9/25/2006 5:33:52 P.M. Central Daylight Time,  grs-pms(at)comcast.net writes:

  	  Quote: 	
		     Bob:

    

   This question came up a few months ago, and I    posted some comments at that time.  You are right, the bolt is    substantially stronger than the AD rivet of the same diameter.  Your wing    won't be any stronger though, since most of the fasteners will still be rivets    which will fail before the bolt can really do its share.

    

   The issue to consider is the fatigue resistance    of the spar.  A driven or squeezed rivet expands to fill its hole    and puts the material surrounding the hole in compression, which tends    to keep fatigue cracks from starting.  An AN bolt in a drilled hole    doesn't have the same effect.  Under normal operating stresses the    material surrounding the bolt feels as though there is nothing in the    hole, and it experiences fluctuating tensile    stress.  Fluctuating tensile stress tends to start fatigue    cracks.  

    

   To keep the fatigue quality equivalent to a    rivet, drill the hole slightly undersize and ream it to the actual    (measured) diameter of the bolt.  Bolts in the standard AN bolt series    (AN3, AN4 etc) have a fairly wide tolerance on diameter, so the nominal    diameter is misleading. What you want is a    fit which is close (or tight) enough that the bolt has to be tapped into    place, not just pushed in with the fingers.  Reaming also makes sure that    the hole is really round, so the bolt is in contact with all the    material around the hole.

    

   For the few bolts involved it might be a good    move to invest in close tolerance bolts in the AN173 series.  They have    the same strength as AN3 etc, but the diameter is closely    controlled.

    

   I have taken my own advice on this issue, using    close tolerance bolts in reamed holes on my CH601 HD spars, where the    factory-built spars needed additional fasteners.

    

   George

    	  Quote: 	
		  	
   



	


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naumuk(at)alltel.net
Guest

Posted: Mon Sep 25, 2006 4:29 pm Post subject: Replacing rivets with bolts

Jim-

     If you don't have the clearance room to rivet,  how in the heck are you going to tap a straight hole?

 Bill Naumuk

HDS Fuselage

Townville, Pa

 [quote]   ---

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