Rivets

 All about rivets

Well not "ALL" about rivets but the rivets used on the Clipper. Here's a reference for most types of rivets.

Solid Rivets

I've found that the majority of the solid rivets used on the Clipper are of the type AN455AD-4-X. 

"AN455" is a specification for the size and shape of the rivet head and is commonly referred to as a "Brazier Head". For any give diameter of the rivet, the Brazier Head is slightly wider than a AN470 "Universal Head" rivet. This wider head helps distribute the load on the soft aluminum.

"AD" refers to the type of the material used. AD means 2117-T4 aluminum. These are sometimes referred to as "structural strength" rivets. They are made with 2117-T4 are identified by the a small visible dimple in the center of the head of the rivet. 

"A" type rivets (ie AN455A-4-X) are made with 1100 aluminum which is nearly pure and relatively soft. "A" type rivets have no dimple, the head is visibly smooth. An important physical property of rivets is "sheer strength"; AD rivets made from 2117-T4 have rough three times the sheer strength of A rivets made from 1100 aluminum.

Another item of note for "A" vs "AD" rivets is that "A" rivets used with 2024 aluminum can apparently lead to galvanic corrosion and some aircraft manufacturers (e.g. Boeing) recommend against using "A" rivets with 2024 aluminum (2117 aluminum rivets are fine). Looking at a galvanic series chart it appears that aluminum alloys have a broad range of potentials and this leads to the possibility of corrosion, but it also appears significantly less than other problem areas that we encounter in the vintage trailer world (e.g. steel vs aluminum).

"-4" is the diameter of the shank in multiple of 1/32", so a "-4" means 4/32" or 1/8".

"-X" is the length of the rivet shaft. This is dependent upon the thickness of the material stack you are trying to fasten together. The rule of thumb is that the length of the rivet should be the thickness of the material + 1.5 times the diameter of the rivet shaft (ie material thickness + 3/16" for a -4 rivet). This added length becomes the "work head" (the part of the rivet that gets smashed/mushroomed) when the rivet is installed. You can buy rivets of a standard length and cut them to the correct size before using them with a special tool.

When repairing the Clipper I'd like to use solid rivets of the type AN456AD-5 (note the 456 vs 455 and the -5 vs -4). These are known as "Modified Brazier Head" rivets. Typically when you remove and replace a solid rivet you need to drill out the hole to the next size up, in our case I'll be going from -4 (1/8") to -5 (5/32") diameter rivets. The function of the "modified" head is that a AN456-5 head is roughly the same size as AN455-4 head so that when you replace the rivet with the larger size the head will appear the same (ie you won't notice the newly replaced rivets). 

HOWEVER AN456AD rivets are hard to find so you're stuck using either AN456A (ie softer, non structural) rivets or AN470AD-5 structural universal rivets. The head size is roughly the same and it's difficult for the untrained eye to tell the difference (the head has a slightly taller crown). In my opinion its easier to spot where a repair has been done with 456 "A" rivets than 470 "AD" rivets because you typically view them head-on (the crown height is not apparent) and the "A" rivets won't have a dimple and that's fairly obvious.

Blind ("Pop") Rivets

Blind, or "pop" rivets are what most people think of when someone talks about using rivets (either that or images of 1920's hot riveting skyscraper ironwork). The are called "blind" because they are inserted from one side, hence the user doesn't need access or is "blind" to the other side. They are commonly called "pop" rivets because most are set by pulling a mandrel that separates from the rivet with a "pop" action and/or noise.

There are a huge number of blind rivets available. Most have "open" ends when the mandrel pops out so they will let air and water pass through. This makes them less useful for exterior applications. However there are some types that are "sealed" or have "closed" ends.

Another type of blind rivet that is popular for aluminum trailer repair is known as an "Olympic style" or shaved head rivet. These rivets work like a typical blind rivet but the mandrel breaks off proud of the head. The mandrel can then be "shaved" down to resemble a solid rivet head. This allows panels to be repaired or replaced with ready access to the back side of the panel.

Blinds rivets can fasten items very securely but they are not considered "structural".

Tubular Rivets

Tubular rivets look a lot like solid rivets but the end is hollowed out. They are set using a pinching mechanism (vs rivet gun) with a die (aka "set") on both ends vs a set on one end with a buck on the "work end". Tubular rivets are not structural but they do fasten metal pieces together well and can be set very thin. They can also be used to form a pivot point in light duty mechanical parts.

For the Clipper the tubular rivets are used in the Hehr "Standard" windows. They are used to fasten the frame together and also as a hinge pin in the window "link levers" that are used to open and prop open the windows.

"Tinners" Rivets

The wheel wells are constructed with galvanized steel not aluminum. The steel is galvanized, ie coated with zinc, to prevent corrosion of the steel. My research led me to the use of galvanized "Tinners" rivets to assemble the wheel wells.

A "Tinner" is a tinsmith. Tinsmiths  make and repair things made of light sheet metal, hence the name tinner's rivet. Tinners rivets come in a variety of materials and are sized based on the approximate weight of 1000 rivets. For example approximately 800 1.25 tinners rivets come in 1 lb of rivets and have a shank diameter that ranges slightly smaller than 1/8". These are known as 1.25 tinners rivets because 1000 would weigh about 1.25 lbs.

I used 1.25 tinners rivets from Hanson Rivets to fabricate the wheel wells. I actually purchased them through Grainger because it was cheapest. I used a flat set in my rivet gun and a standard bucking bar on the "work end". I found they install very much like typical solid rivets.