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Old 08-18-2020, 01:52 PM   #1
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Weld or rivets?

I'm about to start my conversation and will raise my roof. I'm a welder by trade and I am wondering why not weld the skins on instead of using 2000 rivets? Thanks for any information or opinions.

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Old 08-18-2020, 02:21 PM   #2
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That is certainly an option for a cleaner finish.
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Old 08-18-2020, 06:26 PM   #3
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Quote:
Originally Posted by Denis View Post
I'm a welder by trade and I am wondering why not weld the skins on instead of using 2000 rivets?
I think rivets are used in bus construction because it is more cost effective to train someone to rivet rather than weld. I'd imagine in your case, since the labor is "free" welding would be the better way to go.

I would have considered welding some of my stuff, however I'm not comfortable enough with it so used rivet nuts and rivets instead.

Someone please correct me if I'm wrong, but wouldn't welding be technically a stronger joint anyway?
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Old 08-18-2020, 06:56 PM   #4
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If welding-only is done, how would you keep the sheet metal from moving in relation to the hat channels while driving down the road?


I am curious how a welder would tackle this. I like to weld, but short of drilling holes through which to weld to the hat channel (in effect like a rivet would be doing) or with arc welding, simply make a bunch of through-welds to tack in the sheet metal how would you do it?
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Old 08-18-2020, 07:02 PM   #5
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If welding-only is done, how would you keep the sheet metal from moving in relation to the hat channels while driving down the road?


I am curious how a welder would tackle this. I like to weld, but short of drilling holes through which to weld to the hat channel (in effect like a rivet would be doing) or with arc welding, simply make a bunch of through-welds to tack in the sheet metal how would you do it?
I would rosebud weld the skin to the old rivet holes in the hat channel, it would be much more solid than rivets alone. Some of my skins are welded inside to the edge of the hat channel.
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Old 08-18-2020, 08:54 PM   #6
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I would rosebud weld the skin to the old rivet holes in the hat channel, it would be much more solid than rivets alone. Some of my skins are welded inside to the edge of the hat channel.
I have heard of a rosebud tip, but never used one. Is a rosebud weld a weld done with a rosebud tip?
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Old 09-30-2020, 06:52 PM   #7
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My brother is an aeronautical engineer and when i told him my plans for the roof raise he wanted to know why i was even welding the hat channel. In airplanes they rivet EVERYTHING. He says their main issue is stress fractures in the weld which at any altitude isn't ideal but a much bigger problem at 20,000 feet in a pressurized cabin. The follow-up he had was "with enough rivets you can squeeze any metal tight enough it's impossible for water to get through". So his two reasons are stress cracks and waterproofing, the second of which is one I'm willing to take a little more seriously than the first as an issue in my bus.
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Old 09-30-2020, 08:21 PM   #8
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Thats very true about welding, but if you do not put down a continuous bead along the hat channel and square tube (Added inner support) you can prevent hardening the steel where it will crack. On a bus, once it's all paneled together, there really isn't much movement or shouldn't be any for our intended uses.
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Old 09-30-2020, 08:49 PM   #9
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My brother is an aeronautical engineer and when i told him my plans for the roof raise he wanted to know why i was even welding the hat channel. In airplanes they rivet EVERYTHING. He says their main issue is stress fractures in the weld which at any altitude isn't ideal but a much bigger problem at 20,000 feet in a pressurized cabin. The follow-up he had was "with enough rivets you can squeeze any metal tight enough it's impossible for water to get through". So his two reasons are stress cracks and waterproofing, the second of which is one I'm willing to take a little more seriously than the first as an issue in my bus.
Pressurization/depressurization cycles aren't really a big thing in school buses. A better thing to look at than how high-altitude airplanes are constructed is how ground vehicles are typically modified: when a load-bearing beam needs to be extended, an extension is welded and/or bolted on. This is exactly what is done in a typical skoolie roof raise, which also naturally involves the extension of load-bearing beams. I don't know that I've ever seen anyone rivet the rib extensions in place - it would certainly involve a lot more work than welding.

As far as riveting, that is typically the method used to attach new sheet metal to the newly-extended ribs. I have seen people claim that something like this can be made intrinsically watertight just from the riveting, but I've never been able to achieve that myself using my Harbor Freight riveter. All the stuff I've riveted on my bus has been with seam sealer, including around the holes that the rivets go into.
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Old 09-30-2020, 08:56 PM   #10
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Pressurization/depressurization cycles aren't really a big thing in school buses. A better thing to look at than how high-altitude airplanes are constructed is how ground vehicles are typically modified: when a load-bearing beam needs to be extended, an extension is welded and/or bolted on. This is exactly what is done in a typical skoolie roof raise, which also naturally involves the extension of load-bearing beams. I don't know that I've ever seen anyone rivet the rib extensions in place - it would certainly involve a lot more work than welding.



As far as riveting, that is typically the method used to attach new sheet metal to the newly-extended ribs. I have seen people claim that something like this can be made intrinsically watertight just from the riveting, but I've never been able to achieve that myself using my Harbor Freight riveter. All the stuff I've riveted on my bus has been with seam sealer, including around the holes that the rivets go into.
I explained the general relaxed nature of our build compared to the construction of something like a 747. He told me to get the mil depts of all my materials and he'd get me the max load level per rivet or something lol.

I've not seen a roof raise done with rivets but I've seen them done with bolts and lock nuts. Personally I'll chance the vibrations on a weld over a lock nut, but that's just me.

For the record, i plan on welding my roof raise, despite my brother's suggestions. I do believe him on the waterproofing but i think your almost need the rivets touching for them to be THAT affective at waterproofing. I've tapped into my bus air lines and I've got 110psibi planned on running a rivet gun with, hopefully that smoothes the process out a bit.
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Old 10-01-2020, 06:24 AM   #11
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Quote:
Originally Posted by aswallie View Post
My brother is an aeronautical engineer and when i told him my plans for the roof raise he wanted to know why i was even welding the hat channel. In airplanes they rivet EVERYTHING. He says their main issue is stress fractures in the weld which at any altitude isn't ideal but a much bigger problem at 20,000 feet in a pressurized cabin. The follow-up he had was "with enough rivets you can squeeze any metal tight enough it's impossible for water to get through". So his two reasons are stress cracks and waterproofing, the second of which is one I'm willing to take a little more seriously than the first as an issue in my bus.
Keep in mind that many airplanes are made of mainly aluminum. Different animal than mild steel in a bus. Aluminum, when not pre-heated or welded incorrectly, can crack along the "toes" of the weld where the filler meets the parent material. TIG welding as opposed to spool gun with MIG helps decrease the chance of this happening but it takes considerably more time. Additionally, removing a damaged aircraft panel thats been riveted on is much easier than cutting/grinding away welds.
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Old 10-01-2020, 12:08 PM   #12
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welding lap joints in sheet metal between structural members might result in problematic warpage.
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Old 10-01-2020, 01:30 PM   #13
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Well I'm 95% done the welding the sheets on. Just the corners to deal with. I used 4 full brand new 4x 8 sheets on one side. That was nice to work with. The other side I reused the interior roof panels. ******* disaster to work with. They are slightly bent in places making it impossible to weld in place nice and straight. Had to make a relief cut in one to get rid of a "wave". But I am resusing material from the bus and saving around 500$. As for rivets versus welding topic. I feel rivets allow for some movement as welds are ridged. I feel like I will hear some tack welds pop while I am on the road. But the real welds should be solid. I feel like i would use new sheets all round if I did it again.
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