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InterBlog · 07-10-2016, 06:26 AM

I finished trimming out our "back porch" yesterday with visibility tape, non-slip treads, and a cover that I sewed for the cooler. There's some sourcing info in the blog post in case it's of interest to anyone.

And here's a night shot that illustrates why I'm fond of DOT C2 reflective tape. That stuff is amazing.

CUSTOM HITCH CARRIER FOR THE AIRSTREAM INTERSTATE, PART 3: TRIM OUT

unifreck · 07-10-2016, 12:54 PM

INTERBLOG----
Very nice job and well thought out addition to your Interstate. Thank you for sharing your projects with us. AEW

InterBlog · 07-11-2016, 06:54 AM

A short lesson in metallurgy this morning, as it may become relevant to the others of you who use hitch carriers of one kind or another.

LB_3 mentioned above that we had used a hitch tightener to stabilize our hitch carrier. We bought the tightener produced (or at least plated) by StowAway for that purpose.

I had to take the carrier off yesterday so that LB_3 could complete the wiring to the license plate light. I got everything off step by step and came to StowAway’s tightener. This hitch carrier is my brand new toy that took almost two years to realize, so I’m handling every part of it with kid gloves. I didn’t even put a wrench to the StowAway piece – I intentionally got the correct socket (3/4) just to make sure that I was getting it off cleanly, no inappropriate forces applied.

The first nut came off in the expected manner, no issues.

The second nut was seized from the get-go, so I went back into the house and fetched LB_3 and told him that he needed to deal with it because I didn’t want to run the risk of damaging it.

A few minutes later, he came back into the house and announced, “It’s not every day you see galling like that.”

Thus entered a new word into my Interstate vocabulary. Here’s an excerpt from Wikipedia: “

“Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, …. Galling is most commonly found in metal surfaces that are in sliding contact with each other. It is especially common where there is inadequate lubrication between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, aluminum is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.”

In other words, the nut had essentially welded itself to the bolt. The only way to release it at that point was to break it, as shown in this photo below. This phenomenon is different from cross-threading. You can see in the photo that there’s no evidence of cross-threading (such as eroded threads along the length). Just a thoroughly-welded nut.

People sometimes ask me why we are so obsessive about building stuff ourselves. This is an example of why. When we buy stuff produced by someone else, it’s not uncommon for things to unexpectedly go wrong. Not so much when we do the building. A person can certainly live without a hitch tightener, but it’s a nice thing to have, and if it works, it eliminates the need for another method of lateral stabilization (such as the installation of a second, off-set hitch receiver as mentioned above in other posts). This is exactly the kind of failure event I would rather live without if I’m 500 miles from the nearest RV supply place.

Boxster1971 · 07-11-2016, 08:04 AM

This is a common problem with Stainless Steel and Aluminum fasteners. I've had it happen to me in a similar situation. I now use an anti-seize compound on all SS or Al bolts. It's messy stuff but prevents the galling seizures.

https://www.permatex.com/product-cat...ts-anti-seize/

- - Mike
2013 Lounge EXT on 2012 Sprinter

InterBlog · 07-11-2016, 12:40 PM

That is what we're going to try with the next one, yes. I was vaguely aware of this kind of thing but I had previously assumed it only happened with the cheapest of metals. Apparently not.

73shark · 07-11-2016, 01:13 PM

So was the nut a different mat'l than the U-bolt?

I'm still trying to figure out what it does.

LB_3 · 07-11-2016, 10:39 PM

The thread that failed had some minor blemishes on it. Nothing crazy but there was enough added friction when putting the nut on that I remembered it a week later. I didn't see any obvious quality issues when I opened the package so I'm not blaming the vendor. But I'm suspecting that any coating or lubricants were worn off by this increased friction.

I would have expected it to seize right under the lock washer when it was under it's highest load but it wasn't until it had backed off several more threads that it seized up. I'm just going to chalk it up as a random failure and either grease the next one or put a copper anti-seize compound on it.

As for how it works, the ubolt goes over the top of the hitch shank and the plate straddles the shank and the receiver. When you tighten the ubolt it pulls the shank down against the bottom of the receiver which prevents the shank from rocking inside the receiver.

InterBlog · 07-12-2016, 05:36 AM

Quote:

Originally Posted by 73shark

So was the nut a different mat'l than the U-bolt?

I'm still trying to figure out what it does.

Concurrent with your question, I got an off-Forum question about departure angle and how might a contraption like ours impact an EXT?

So I put both clarifications on one diagram. The inset shows the position of the hitch tightener, which basically keeps the whole contraption from slightly rocking back and forth due to the play in the fit between shank and receiver. It's a good addition - when I step on it, I don't want to feel it go CLUNK! That seems so gauche in an otherwise-elegant design.

The question about departure angle was a good one. When we were mocking this thing up in half-made form, my knee jerk reaction to LB_3's initial frame design was, "Nope - raise it up!" because if it were set at the original level of the hitch step (which was our first idea), it might have impacted departure angle, especially if there were a non-planar surface involved (which describes pretty much every travel surface in my home province of Nova Scotia).

So we vaulted it slightly so that its upper surface sits just below the top of bumper. It's also not as wide as most commercial carriers, so that also minimizes potential impacts on departure angle.

Protagonist · 07-12-2016, 05:53 AM

Quote:

Originally Posted by 73shark

So was the nut a different mat'l than the U-bolt?

You don't need dissimilar metals for galling to occur. In fact, you don't even need metals— you can gall plastics, too. Galling is different from galvanic corrosion.

Galling is accidental friction welding (which should actually be called friction forging), a technique that— when done on purpose— has been recognized by the American Welding Society since the 1950s.

Boxster1971 · 07-12-2016, 09:43 AM

Quote:

Originally Posted by Protagonist

You don't need dissimilar metals for galling to occur. In fact, you don't even need metals— you can gall plastics, too. Galling is different from galvanic corrosion.

Galling is accidental friction welding (which should actually be called friction forging), a technique that— when done on purpose— has been recognized by the American Welding Society since the 1950s.

Right on Protag! In my my case I fused the stainless steel (SS) nut to the threads on a 1/2" SS bolt that is part of my DIY hitch carrier. The torque on this connection was enough to fuse the nut and bolt together and I quickly twisted that 1/2" SS bolt. Now I use anti-seize compound for such connections.

- - Mike
2013 Lounge EXT on 2012 Sprinter

InterBlog · 04-29-2017, 06:56 AM

This older thread originated because the OP was looking for a place to store a dog pen in, or on, an Interstate.

I found this pic on Instagram last night and thought I'd re-post it FYI. Yet another new take on a storage challenge. I do agree with the Instagrammer that custom is often the best way to go with these things. That way the device fits the owner's needs exactly.

InterBlog · 09-25-2018, 03:56 PM

Appending another interesting photo to this thread because it was probably the most in-depth historical thread on roof storage options.

Gulf Freeway, stuck in traffic yesterday. Really nice rear ladder - big and beefy, not those thin little rungs that will hurt your feet. Really nice roof support system. I don't recall ever seeing either of these products on any high-roof van previously. They are obviously commercial products, not consumer products, but they might do justice to a kayak or two.

Don't ask me why Charlie has no eyeballs. I don't know the answer to that part. Maybe because he sees no evil from the top of that fine ladder?