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.

Subfloor Material

Advantech Subfloor

Just a short post to discuss my downselect of subfloor material to Advantech by Huber. I special ordered it via Home Depot for about $60/sheet (including CA fees and minimum order costs). This is actually much cheaper than my 2nd choice which was marine grade plywood (which I used in the Boles Aero), and I won't need to use penetrating epoxy as a sealer.

I was considering the following options:

1. Coosa Bluewater 26 - suuuppppeeerrr expensive composite that won't rot
2. Marine grade plywood - expensive but less prone to rot than normal plywood
3. Advantech or other engineered subfloor

After much deliberation I chose Advantech. It's an engineered subfloor specifically designed to withstand soaking moisture during the construction of a home. The first time I read about it I was repelled because OSB is notorious among the trailer restoration crowd and Advantech looks like typical OSB. But after some investigation I found that it's being adopted by vintage trailer restorers, particularly when they don't want to spend $300+ per sheet for Coosa board.

I had some initial difficulty finding it but contacted Huber Engineered Woods and they recommended that I special order through my local lumber store. It's not a normal stock item because local contractors won't spend the extra money to use it. Generally only large corporate builders use it because they recognize the cost tradeoffs associated with rework.

In any case it took about 3 weeks to get it delivered to the local Home Depot, but it's now in my garage waiting to be installed. It's the nicest and most uniform sheet good I've ever unloaded. Hopefully it lives up to it's promises.

Wheel Wells

Wheel Well Fit Check

The wheel wells need to be placed on the frame and under the subfloor to prevent water thrown up from the road from rotting the subfloor. I was excited about installing the subfloor when I re-remembered this step. So I stepped back and went about fabricating new wheel wells.

The wheel wells for my Clipper were missing (along with most of the interior walls, etc. Based on internet posts I believe the original wheel wells were constructed from simple plywood boxes. The only remnants of those boxes was the outer aluminum wall that is riveted to the inside of the exterior trailer skin.

Remnant of Original Wheel Well

I had decided a while ago that I'd fabricate some new wheel wells. I really didn't want to use plywood boxes that would rot out fairly quickly because replacing them would mean tearing down the entire trailer.

I considered several alternatives but ended up designing a simple wheel well and ordering the metal pieces from SendCutSend. I'd considered purchasing sheet metal and cutting it myself, but after pricing in shipping, handling and waste it was going to be about the same price.

I ended up using 0.036" G30 galvanized steel which falls somewhere between 22 and 20 gauge. That's pretty stout for wheel wells and "the internet" said it was a much better choice than using aluminum because it's stronger. The G30 designation indicates how much zinc is deposited for corrosion protection (G30 is on the low end). I would have preferred G90 grade which has more zinc deposited for rust prevention but it was not available when I ordered. Later I'll talk to some additional efforts I made to prevent corrosion.

Laser Cut Parts from SendCutSend

Each radius of the wheel well is made of 3 identical cut pieces. The sidewalls for each wheel well are 2 identical cut pieces (6 and 4 total for the 2 wheel wells). I've found that ordering a quantity of 4 or more from SendCutSend is the "knee in the curve" for pricing so when possible I make design choices that allow for part commonality. In this case the wheel well is slightly taller than required (3" above the max axle loading deflection per Dexter) so that I could use a common design for the radius pieces.

I used my 36" straight sheet metal bending brake to make the appropriate bends. Of course I misbent a couple bends on the first one and had to hammer them back (which is do-able with steel) and rebend it.

Parts Bent into Shape For Assembly

For assembly I wanted to make encourage corrosion prevention. I considered a few options but settled on using galvanized steel "Tinners" rivets. These are flat head rivets used by "Tinners", ie sheet metal fabricators. I'd never heard of them before but they are available from Hanson's rivets and their distributors. I could find very little on the internet about their use. The sizing is odd compared to other rivets: they are sized according to the weight of 1000 rivets. I used a 1 1/4 lb rivet which is just under 1/8" diameter (Hanson Rivet part number TRSL01.25) which gives about 800 rivets per pound.

Small number of 1 1/4lb (1.25) Tinners Rivets

Drilling and setting these rivets is almost identical to the aluminum ones except they have a flat head vs a "universal" or "Brazier" head. I used a flat rivet set on my rivet gun. The lack of a domed head to center the gun was a little challenging but not much of a problem - fortunately no one will be able to see the few occurrences where the gun skipped off the rivet head.

As is my practice with the aluminum skin panels, I used Sikaflex 221 between the panel seams. So the process is clamp; drill, cleco, drill, repeat; disassemble; spread Sikaflex 221; reassemble with clecos; rivet removing clecos as you go. The Sikaflex makes it a little messy where it squeezes out but it's easy to clean up.

Wheel Well Assembly (1 of 4)

Wheel Well Assembly (2 of 4)

Wheel Well Assembly (3 of 4)

Wheel Well Assembly (4 of 4)

Once assembly was complete I sealed the inside seams with a liberal application of Sikaflex 221. Then I sprayed the inside with Rustoleum Professional Grade Rubberized Undercoating Spray. It took a can for each wheel well to accomplish the 2 recommended coats (wear a respirator!) I chose the Rustoleum product based on some YouTube comparison videos. It's not as thick as I'd imagined and I'm a little concerned about durability. I was hoping for something similar to bed liner. 

I also sprayed the outside of one sidewall on each wheel well. The outside of the sidewall will sandwich up against the inside of the trailer's aluminum skin and be riveted to it (it replaces the aluminum box side in the image towards the top of this post). The zinc coating of the galvanized steel should prevent dissimilar metal corrosion between the wheel well and the trailer wall but I thought an insulating coat of rubber wouldn't hurt.

Wheel Wells Drying after Undercoating

One last note. One of the sidewalls of each wheel well is not flanged. That sidewall will be riveted to the inside wall of the trailer. I left the sidewall long and plan to trim it to the shape of the exterior wheel well after I wove the shell onto the new frame. I did trace the old wheel well onto the new sidewall, but I'm not 100% confident of the final fit of the shell on the trailer so I wanted to leave myself some wiggle room.

Dry fit of the new Wheel Wells

Overall I was very happy with the way this subproject worked out. It was fairly straight-forward, not too time consuming, and reasonably priced (about $250 for materials).