As you said Anthony, they are designed to twist...........but they are built to a specification that isn't twisted during the building process, and they pretty much return to that original spec after twisting under an applied force. Building a chassis that is not square in the building process or that starts out square and warps when welded isn't the same as twisting somewhat and then returning to the original spec. I agree with you though that a certain amount of flex is a good thing in most vehicles, buildings, bridges, and even spacecraft.
It’s all random thoughts that rattle in my head. We built a boxed chassis for a 33. It smacked a tree. Being boxed and with a DOM tube X member in the center, it wasn’t feasible to repair it. The boxing on one side and half tbe X bracing would have needed cut out. The same hit on a non boxed frame with rivited X bracing would have been repairable. However, would that type of chassis handle the big block and stick that was in that 33? Kinda like the difference between fixing a modern fully welded chassis vs an older chassis. How much extra bracing/boxing does the average low to mid 300hp street car need? That’s kinda what I wonder Aesthetic wise,I dig a step boxed rail with holes. Extra point for dimple dies being used. How much strength does the dimple die add
How important is it that I get complete weld penetration to the very core of the "thick tapered part" of structural channels and beams?
I'm not following your description, but full weld penetration of what you're welding is very important.
Yep, but good ones. My random (untested/unproven by me) thoughts are that many of the older frames aren't sufficient for high torque motors and bigger tires, and they need some help. Boxing gives more strength and is somewhat simple to do. It also gives a nice finished look if done well. It can also seal the inside of the frame from the elements. It also adds weight, and can trap moisture. With todays CNC plasma cutters, someone could lighten the boxing plate by designing a cut out pattern of some type, and still get the added strength. But it would be difficult to paint the backside and it might also collect leaves and crud more readily. Again, random thoughts.........so it's kindof a choice of which factors are more important to the builder. As far as crossmembers go, I'm more of a fan of the 1x2 box tubing set up. I just like the way they look and they are easy to make and fit to a chassis.
My goofy thought for painting the inside would be use a wand attachment to shoot the inside with epoxy. We used that for cavity wax. Should work for epoxy
As far as protecting the inside of a frame, it's best to plan ahead when boxing. Eastwood (and others) have you covered with products like this: https://www.eastwood.com/eastwood-internal-frame-coating-14oz-aerosol.html Weld-through primer on areas to be welded helps to make sure you won't have any unprotected spots in the frame, and you can also pre-paint areas of the frame and inside of boxing plates that are away from the weld zones for protection. The boxing plates you describe have been available for 10+ years for many common applications, such as these from Wolfes: https://www.wolfesmetalfabrication.com/boxingplates.html I got the solid ones from Wolfes for my Model A because I won't know the placement of my crossmembers until after the frame is boxed. I also like their Easy Weld design which allows a nice fillet weld. There's also a couple of hot rod parts companies that sell weld-in oval access doors for boxed frames. This is one example, can't find the other one I remember: Frame Access Doors – York Speed Shop
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