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Please stop throwing generalized internet engineering tropes at the wall. Just because it all looks like rocket science to someone who doesn't have industry ex

Please stop throwing generalized internet engineering tropes at the wall. Just because it all looks like rocket science to someone who doesn't have industry experience doesn't mean it is. The repairs you are proclaiming to be impossible are perfectly possible to do with good results. These repairs are often performed often, just not in the high cost of labor parts of the world where HN lives (the low cost areas buy our wrecked cars to fix and sell to the point where sourcing parts for major repairs is often easier there than in the vehicle's country of origin). There's autobody industry specific tools and literature that help professionals in the industry perform the repairs properly. It's perfectly possible to take a car apart and reassemble (with good parts) the way an OEM would have if you're willing to invest in the tooling (mostly for welding in hard to reach areas). Car passenger cabins aren't supposed to flex (but in practice they do so within acceptable limits) and OEMs provide service literature telling you what you can and can't modify, much repair info can be gleaned by reading between the lines of such service literature. The welding issues you are describing are simply not an issue for skilled welders. Your opinion of engineering education is hard to reconcile with the observed performance of new engineers in any/every field.

blagie 6y ago
Did you even read what you were replying to? The conclusion of what you're replying to: "You can fix up a $100 Huffy with any old welder. A $2000 steel frame with thin-wall double-butted tubes? You want a really skilled welder and close inspection to make sure it's not compromised." Yes, it's possible, and yes, I know folks whom I'd trust to do it. The guy in my local auto shop? Definitely not. Random car shop in the developing world? I've seen the results. They'll drive, but they're far from save by Western standards. What you wrote: "if you're willing to invest in the tooling" "The welding issues you are describing are simply not an issue for skilled welders" I mean, seriously. You responded to a something entirely different from what I wrote, repeated roughly what I actually DID write, and mixed a few errors in (if car cabins weren't made to flex, they'd be using a very different type of steel; virtually everything made to be tough is made to flex). Please find a place in my post where I "proclaiming [repairs] to be impossible"
- VBprogrammer 6y ago
  Anyone who has jacked up a car at one wheel and tried to open a door knows that flexing is very real.
  - throwaway0a5e 6y ago
    > Anyone who has jacked up a car at one wheel and tried to open a door knows that flexing is very real. Have you tried doing that to anything other than a 1960s convertible? My 90s junk handles that just fine (and they're not particularly rigid cars). Matter of fact I did it yesterday afternoon to change rear pads. Generally speaking you need to get a floppy vehicle really bound up (think 80s Jeep Cherokee or minivan off road) in order to have issues with doors and even then it's usually rear hatch only. OEMs specially try to avoid having bodies that flex enough to be noticeable to consumers, let alone to the point of doors not opening. Heck, I'd be surprised if you can even design a car to pass modern roof strength requirements without also making it stiff enough to have the doors open and close regardless of how bound up it is. (Pickup tailgates are another thing since the bed is open top and bolted to a frame designed to flex somewhat and even then being able to open the tailgate with two tires off the ground is not unheard of)
    - dekhn 6y ago
      When I gave a friend a ride in my 2001 Miata, the very first thing he said was 'huh, you have a rigid frame, if I'd done that turn in my old MG, you could see the frame flexing'
      - jacquesm 6y ago
        Old MG is bodypanels over chassis, a Miata is a unibody. Totally different construction.
  - blagie 6y ago
    Work is force times distance. How tough your car (or anything else) is depends on: 1) How much force it takes to flex it -- the spring constant 2) How far it will flex before it breaks Multiply the two together (or specifically, 1/2 kd^2 where d is how far it will bend before it breaks, k is the spring constant, and 1/2 kd is the average force you're applying), and you get how much energy it takes to break it. *Everything* flexes. Rigid things just flex less for the same force. Things which break when flexed just a little bit are called brittle.
dekhn 6y ago
I disagree; I think the person you're replying to is completely correct. To rebuild the safety of a modern engineering system isn't somebody in their garage can easily do. With skills, you can definitely improve things, but not to the statistical level that modern car manufacturers have achieved. It's similar in microelectronics. I can do a ton of stuff with an arduino because it uses really basic old, tough eletronics. I can put too much current into a pin, ok the pin dies but the AVR is still fine. A modern ESP32? A little bit of current or voltage above the rating and the whole thing is toast.
- phaedrus 6y ago
  It's a numbers game, and you're overlooking the other side of it. The automakers have to engineer to a very low probability of failure because they deal in large numbers. It's true a person in their garage can't match that engineering - but they don't have to. They only have to get to "reasonably" safe not "absolutely" safe. It's just like people putting turbochargers on their 90s Hondas. Naysayers could claim it's a fool's errand because if Honda, with all their engineering resources, didn't feel they could add turbocharging to their engines in the 90s and have it be cost effective and reliable enough, surely someone in their garage can't do it? But what they overlook is that if 5% of one of Honda's mass market cars blew an engine that would be a disaster, whereas a 5% chance an individual blows his own engine, which he may be able to replace for $500 to $1500: that may be a risk an individual is willing to take that a carmaker cannot.

blagie 6y ago

Did you even read what you were replying to? The conclusion of what you're replying to: "You can fix up a $100 Huffy with any old welder. A $2000 steel frame with thin-wall double-butted tubes? You want a really skilled welder and close inspection to make sure it's not compromised." Yes, it's possible, and yes, I know folks whom I'd trust to do it. The guy in my local auto shop? Definitely not. Random car shop in the developing world? I've seen the results. They'll drive, but they're far from save by Western standards. What you wrote: "if you're willing to invest in the tooling" "The welding issues you are describing are simply not an issue for skilled welders" I mean, seriously. You responded to a something entirely different from what I wrote, repeated roughly what I actually DID write, and mixed a few errors in (if car cabins weren't made to flex, they'd be using a very different type of steel; virtually everything made to be tough is made to flex). Please find a place in my post where I "proclaiming [repairs] to be impossible"

VBprogrammer 6y ago
Anyone who has jacked up a car at one wheel and tried to open a door knows that flexing is very real.
- throwaway0a5e 6y ago
  > Anyone who has jacked up a car at one wheel and tried to open a door knows that flexing is very real. Have you tried doing that to anything other than a 1960s convertible? My 90s junk handles that just fine (and they're not particularly rigid cars). Matter of fact I did it yesterday afternoon to change rear pads. Generally speaking you need to get a floppy vehicle really bound up (think 80s Jeep Cherokee or minivan off road) in order to have issues with doors and even then it's usually rear hatch only. OEMs specially try to avoid having bodies that flex enough to be noticeable to consumers, let alone to the point of doors not opening. Heck, I'd be surprised if you can even design a car to pass modern roof strength requirements without also making it stiff enough to have the doors open and close regardless of how bound up it is. (Pickup tailgates are another thing since the bed is open top and bolted to a frame designed to flex somewhat and even then being able to open the tailgate with two tires off the ground is not unheard of)
  - dekhn 6y ago
    When I gave a friend a ride in my 2001 Miata, the very first thing he said was 'huh, you have a rigid frame, if I'd done that turn in my old MG, you could see the frame flexing'
    - jacquesm 6y ago
      Old MG is bodypanels over chassis, a Miata is a unibody. Totally different construction.
- blagie 6y ago
  Work is force times distance. How tough your car (or anything else) is depends on: 1) How much force it takes to flex it -- the spring constant 2) How far it will flex before it breaks Multiply the two together (or specifically, 1/2 kd^2 where d is how far it will bend before it breaks, k is the spring constant, and 1/2 kd is the average force you're applying), and you get how much energy it takes to break it. *Everything* flexes. Rigid things just flex less for the same force. Things which break when flexed just a little bit are called brittle.

dekhn 6y ago

I disagree; I think the person you're replying to is completely correct. To rebuild the safety of a modern engineering system isn't somebody in their garage can easily do. With skills, you can definitely improve things, but not to the statistical level that modern car manufacturers have achieved. It's similar in microelectronics. I can do a ton of stuff with an arduino because it uses really basic old, tough eletronics. I can put too much current into a pin, ok the pin dies but the AVR is still fine. A modern ESP32? A little bit of current or voltage above the rating and the whole thing is toast.

phaedrus 6y ago
It's a numbers game, and you're overlooking the other side of it. The automakers have to engineer to a very low probability of failure because they deal in large numbers. It's true a person in their garage can't match that engineering - but they don't have to. They only have to get to "reasonably" safe not "absolutely" safe. It's just like people putting turbochargers on their 90s Hondas. Naysayers could claim it's a fool's errand because if Honda, with all their engineering resources, didn't feel they could add turbocharging to their engines in the 90s and have it be cost effective and reliable enough, surely someone in their garage can't do it? But what they overlook is that if 5% of one of Honda's mass market cars blew an engine that would be a disaster, whereas a 5% chance an individual blows his own engine, which he may be able to replace for $500 to $1500: that may be a risk an individual is willing to take that a carmaker cannot.