Skinning - Steel Gauge

[CapN-SKO]

This sounds interesting I’m going to have to follow this as when I get my bus I’d like to raise the roof as well

 

[gclarkv]

Do I understand you to say that a professional shop recommended 26ga steel for your skins? If so...well, let's just say that makes me skeptical of their ability to perform satisfactory work.

 

[EastCoastCB]

Do I understand you to say that a professional shop recommended 26ga steel for your skins? If so...well, let's just say that makes me skeptical of their ability to perform satisfactory work.

THIS^ is correct.

 

[Tango-SKO]

Must usually work on stix & staples. 26 ga. isn't really sheetmetal. It is "foil".

 

[kidharris]

When I strip the bus and build an RV I become the manufacturer of that vehicle and I alone set the GVWR to what I want. There is no benefit to change it to a higher GVWR because the fees go up accordingly. But I can lower it to less than 26K lbs for my build and as long as I don't exceed that I'm good, and the registration fees drop substantially.

Do you live in Arizona?

 

[CapN-SKO]

So would you run a bead on the inside after installing the siding?

 

[kidharris]

So we are outsourcing our roof-raising needs, which is going well so far. We've just been quoted for the new steel to skin the sides, two options and I wanted to source some advice -

26g 'Flashing' for $390

or

20g for $979

Steel isn't my forte. Hence the outsourcing. We are committed to making the bus as strong as possible but wondered if there was a discernible difference between thickness for skinning? The fabricator said that he was concerned about noise levels ('tin canny-ness') with the thinner stuff, but when I said that we'd be spray foaming he said that this wouldn't be an issue.

Any thoughts?

I worked sheet metal for many years and (not trying to be a smarty) I have seen some of the crappiest work i have ever seen on some of these schoolies. In the interest of sorting this issue out I am going to pass on a few pointers.


Thicker gauges are stronger structurally, but not the end all that some believe it to be and don't always stop the "wrinkly/ripply" (oil canning) that you see on most of these buses. The oil canning happens because the metal is a relatively flat sheet in 1 plane. The window pillar structures that you are fastening it to are not in a perfectly flat plane and when you fasten to them you are causing the metal to conform to these many highs and lows which causes oil canning. Residual stresses in the sheet from manufacturing and uneven clamping pressures of the fasteners also contribute. It is pretty much impossible to stop if you use flat sheet. The better the job of getting the pillars aligned the better the sheet metal will look. I don't think you can stop it, but you can minimize it.



Thicker metals allow relatively larger expanses (widths) of exposure with out noticeable oil canning but come with a significant price and weight penalty. More than 2-8 inches of exposure, depending on thickness, is usually going to oil can in lighter flat sheet.


The main solution used is to combat this is to corrugate or put bends or even textures in the metal. These add strength and drop the flat exposure down. If you look around at professionally manufactured goods and see bends or textures in the metal, many times this is why. Even car panels are never flat but will have some compound curve and bends (modern car panels are also made with high strength, heat treated steels, which is why they can be so thin). The larger the corrugations are the more noticeable and stronger they are. The "rub" rails on the bus are there to help break up and strengthen the wide unbroken sheet metal exposure They are not there so you can rub the bus up against something. The trick is to make the bends/corrugations visually appealing. Using smaller/narrower pieces can help, but can also lead to other problems. Corrugations don't work well with windows.



Installation procedures are also critical. Fasteners should be evenly installed from the center out to prevent trapping a "wave" in the panel and/or under lying structure, kinda like installing wallpaper or decals. Think about it...If you fasten 2 corners and the metal is not perfectly and evenly flat there is a slight curve (air gap) where the metal bows up away from the structure. If you then put a fastener in the middle you now broke the curve into 2 curves. Add more fasteners and create more curves (waves). Professionals use temporary easily removed fasteners called cleco fasteners to help mitigate this, especially when riveting. Fastening from the center out and using temporary clecos to hold the metal in place helps mitigate this.


Don't use excessively long pieces. Besides being hard to handle they can create problems with expansion and contraction from temperature changes (especially aluminum) and may need to have expansion joints provided, depending on design. This is a bigger problem if you are mixing materials with different expansion coefficients (ie. steel structure & aluminum skin).


How the metal is cut can also add ripples. Check out some work put out by the shop and see if it is satisfactory to you before ordering. Also check with the shop making the metal for suggestions, they know their equipment, metals, and capabilities. Most fabricators can also weld 20/22 ga but may have a problem with 24/26 ga. Welding/soldering/brazing may be necessary to put in widows/doors or other penetrations or add ons.


There are many more tricks, to many to post here, but I hope this helps you. I would go for the 20 ga (maybe 22 ga) and price shop it. The 26 ga is not going to contribute much strength. If my pillars seemed flimsy I would go heavier, 16/18 ga and more fasteners. Structurally, if you slightly overbuild you only have to pay for it once. Who knows how many times you will have to pay for it if you under build. Of course, you have a budget to deal with.

 

[kidharris]

Here's a definition that came from the interwebs...

The gross vehicle weight rating (GVWR), or gross vehicle mass (GVM) is the maximum operating weight/mass of a vehicle as specified by the manufacturer[1] including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers and cargo but excluding that of any trailers.[2] The term is used for motor vehicles and trains.

The weight of a vehicle is influenced by passengers, cargo, even fuel level, so a number of terms are used to express the weight of a vehicle in a designated state. Gross combined weight rating (GCWR) refers to the total mass of a vehicle, including all trailers. GVWR and GCWR both describe a vehicle that is in operation and are used to specify weight limitations and restrictions. Curb weight describes a vehicle which is "parked at the curb" and excludes the weight of any occupants or cargo. Dry weight further excludes the weight of all consumables, such as fuel and oils. Gross trailer weight rating specifies the maximum weight of a trailer and the gross axle weight rating specifies the maximum weight on any particular axle.

In some states, like Arizona, when you register a truck you can specify the GVWR. I was shocked when they asked me what GVWR I wanted to register it as. Smaller GVWR = smaller reg fee and they print you a new title with the new GVWR on it. Now you have 2 things to get in trouble for when the Highway Patrol stops you and puts you on the scales. You can not exceed the weight on your title and you can not exceed the weight posted on the vehicle by the manufacturer. I believe that this can be a help if for example your original weight on the vehicle is puts you a small amount over some fee schedule, then you can reg it as slightly lighter and get the smaller fee. However, you are legally bound to the new GVWR. I did not ask them if I could go higher than the truck was originally rated for. I just stuck with my original GVWR because who knows what another state might have to say about this. Also...what happens if your drivers license is only good for the GVWR on the new title but the highway patrol wants to go by whats posted on the vehicle?