Tube Frame Safety / Design

[fabr]

 Both cars are for recreational sand use. Both would be very unlikely to be unduly unsafe for that purpose. Do I feel safe riding in lightly built sand cars ,such as those shown, in general ? No. For the same reasons you pointed out but I also know that the cages as was the question about those cars,I think, are going to serve the purpose in a rollover. I wouldn't WANT to ride in either one tho.

[BDKW1]

I'd call that first car Orange Crush but I'd add 'and stab'. Both cars lack critical support members, whether they can manage to survive a rollover or not, but the second car is better thought out.

What an indescribable horror if the first car hits REALLY HARD the wrong way. Instant apendectomy & colostomy as those control arms come ramming into your guts? One should never design such that a component can ever reach the driver in a crash. Scary with that ultra-long shock on the rear too, in that respect. Could end up with your head resembling a shish-kabob? Should have a loop of tube around them as a guide for where they'd go if top shock mount broke loose at impact or a hard landing, also to prevent pole vaulting.

Also needs diagonal supports at lower points of roll cage, from about steering wheel height down to top rail at a minimum in front, slightly higher and connecting farther forward on top side rail at rear hoop. Without those a weird end-o could collapse the cage at a top-rear impact.

The sides appear to be ladder frame sections by the screws in the side panels? I'd say triangulation is much preferred, using diagonals? Would also be nice to have a horizontal tube about shoulder height behind driver/passenger for some 5-point belts and to help prevent seat fold-over? I would have also run a horizontal bar across the forward shock support hoops to stabilize. All that would only add what, maybe 10 pounds?

Second car could use the front & rear diagonals too, and both cars need a u-joint in the stab-me-hurt-me steering shafts. Second car gets huge extra points because no frame or chassis member could intrude into driver seating area to impale or injure driver. It could use a horizontal cross-chassis tube right about at rear mounting of front diagonal roll cage support tube, where verticals tie in, to cut down on frame flex.

I think your imagination is getting the better of you and you haven't seen many crashed cars.

[JimmieD]

I think my 45 years of hands-on experience including tubular spaceframe & monocoque chassis design keeps my imagination on the reality side. I learned the basics from Maserati and Alfa Romeo [I think Typo 159's] and then Mercedes 300SL cars, and Colin Chapman when I worked with Lotus and Lotus/Ford, and as a pit crew chief with Lotus, in addition to my work with Volvo and their Rallye efforts, and Datsun with some of their racing before they were renamed, plus some years playing with various personal designs. Unfortunately many home builders have no idea of basics and sound fundamental engineering principles and tend to go with cool and flashy instead of intelligent. To each his own.

[fabr]

Whoa,whoa,whoa. Slow down there Trigger. LOL!  You've stated a lot of impressive stuff there but in no way have you let us know in what capacity you were involved or with which crews. Claims of that kind should be supported by letting us know the story behind the man. I can't argue with what you say about cool and flashy but on the other hand we must consider the application when designing ,not too much and not too little, for the actual application.  I'm SURE that the names dropped do just that.

[BDKW1]

Also mostly street oriented.
 
For example, your comment

  What an indescribable horror if the first car hits REALLY HARD the wrong way. Instant apendectomy & colostomy as those control arms come ramming into your guts?

I've seen plenty of that type of front end crashed. The arms fold. Nothing ever came into the cab........ Except a lot of dirt........
 

Scary with that ultra-long shock on the rear too, in that respect. Could end up with your head resembling a shish-kabob?

I have seen shocks bent, ripped in two, mounts broken. Have never seen one get anywhere near someones head. Not saying it's imposable, just highly unlikely.
 
While I agree that those chassis could use some diagonals in the rear hoop and roof area, they are far from death traps. The Funco's are actually some of the better built cars out there.
 
Basically they are sand cars not race cars. People that want to drive them like race cars are prime Darwin candidates............

[JimmieD]

I'd say my reply was correct considering the post preceeding it: "I think your imagination is getting the better of you and you haven't seen many crashed cars."

So, my response is that I've been around the block a few thousand times, and have certainly seen my share of wrecks, minor and spectacular, and have of course been in quite a few too. Who I am now is an old toothless hillbilly nobody who plays around building some stuff, but it's pretty good stuff for what it's designed for.

Yes, most of my early experiences were asphalt and high speed. Other is sand, dirt & offroad. But whatever a person is designing in a vehicle there should NEVER be any component that can easily or potentially enter the passenger compartment and injure people in a crash.

I wouldn't personally ride in that orange car without a hoop around the rear struts, at a minimum. The forward control arms could also enter seating area in a hard & fast wreck, so that's something I wouldn't want to experience either. I have no idea what powerplant is in it for top speed, and nobody said anything about sand use only.

I'm not young anymore, don't suppose I ever will be now. In the long past I've got a long list of friends: dead, injured, maimed, paralyzed or veg cases you water once a week, and many of the more serious were due to fatal design flaws, and stuff folks never imagined would happen. When you come to a wreck and the impact was so hard it tossed a 600lb V8 600 yards on impact after ripping it out of the motormounts and through the radiator support it makes you stop and think, especially if a friend was inside. Nobody would have imagined. I do imagine now, and imagine the worst that could happen in a wreck, and it pays off. I was suggesting that to others, due to the nature of the original post and topic.

For all of us, it's a matter of better safe than sorry. I'm not out for a fight or bragging rights, just don't want anybody to get hurt if they don't have to.   
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[fabr]

I doubt anyone here will disagree with most of what you said there. We,as a site,IMO are more safety oriented than most any site out there. We wish to make that clear. However there is no way for a car to be "safe". There's just no such thing. There are SAFER cars though and therein lies the issue. Safety can be as much as possible with every gizmo and gadget imaginable or it can be   ,and is usually, as much as the designer is willing to put in it and/or the level of safety that is acceptable to the buyer or that the buyer will even use. ALL sand cars and many ,many ,many other cars of all types COULD be made safer. Just my 2 cents.

[nvheattreating]

What does heat treating mean?  It usually means "strengthened".  For 4130 that means hardended and tempered.

If you were talking about heat treated aluminum, it would also mean "strengthened" but would be "solution treated and aged".

But as you mention, annealing, normalizing, aging, precipitation hardening, etc. are all heat treating processes. 

Usually is something is annealed, it is not called heat treated, since it has only gone thru a softening process and has not been strengthened but rather weakened.

[fabr]

I agree with that as   most ,if not all, of us generally do.The thing though is that in the HT industry normalized indicates a fairly narrow range of heat treating process. Also , hardened to most of us means much harder than normalized and therefore more brittle. Along those lines along with the fact there was a well respected builder welding hardened 4130 which is a no-no no matter where you look up info on welding 4130 is just amazing to me and I have to agree that NHRA's willingness to be so lax on the certification of the chassis is just inexcusable to me.

[JimmieD]

My apologies. I think my words often read diffferent than they get thunk on this end.

For a lot of us who hit 'middle age' things change. Like a friend said, "Id feel a whole lot better about it if I knew of more people 120 & 130!" We've seen the crazy stuff that 'could never happen' become commonplace. It happened to me.

Worked a job that included some painting, not something I normally did. Just painting some steel, no big deal. Next thing I knew I was laying in a bed paralyzed, blind and stone deaf! Company owner decided to save 5 bucks a gallon on the case of paint, and that was on a half million dollar retooling job!

It was paint only to be used on offshore oil rigs: wear a full air-tight suit, cuffs taped to gloves and booties, full hood & air fed respirator. He didn't mention that part, no MSDS available, so I used it completely unprotected, for 3 days.

Thank God, literally, I'm slowly recovering. Sight & hearing is back 100%, mobility fairly good, but I'm disabled for life. There's no treatment for it and every day is a challenge. So, I look a lot harder at safety, and try to envision the hidden dangers in anything.

Play hard guys, have fun, but be safe, please be safe.

[fabr]

Sounds like Imron paint.  Got a buddy with similar experience when it first came out 20 or so years ago -before anyone knew better. You might be fine the first time or even first several times but when your body said it was enough you ended up in the hospital with life threatening issues and the accumulative effect never goes away .Any further exposure of any kind will put you right back in the hospital -possibly dead .No matter,hope you get to near normal.
 "Play hard guys, have fun, but be safe, please be safe." Great advise and much appreciated. On a serious note ,I will reinforce the sites POV on safety, --ALWAYS USE safety equipment and design things as well as each of us can with safety always in mind.
 

[nvheattreating]

I don't have any experience with welding 4130, but there is another problem that can be created.  In thin wall 4130 it can actually cool fast enough in air after welding that it hardens in the heat affected zone.  Care should be taken to slowly cool any welded areas on these frames.  Pouring water on a hot weld or fan cooling it would only make it worse.  A good practice would be to stress relieve the welded frames after welding, but there aren't many furnaces large enough to accomodate that task.  If you do decide to stress relieve the frame, make sure you have all cavities of the frame vented to allow for expanding gases to escape.

All of this is of less concern if you use lower alloy grade steels with less hardenability.

[fabr]

Most of us in the buggy fabbing world know of the issues of the HAZ. Careful attention to welding heat and size of HAZ is very important. IMO the worst thing that is done is the practice of welding the joints in 4 90* arcs. IMO that creates what you are referring to when welding thin wall 4130-too much heat.

[Nutz4sand]

IMO the worst thing that is done is the practice of welding the joints in 4 90* arcs.

I have actually seen this suggest a lot to be done this way. B ut with nothing to back it up of course. In an odd way it seems to make sense so I think thats why it gets spoke of to do it in the 4 90* arcs.  I try to go as far around a tube as I can in one shot access permitting.

But whats the best really?


EDIT:  I must add that I do not use 4130 as I feel its way overhyped and actually more dangerous if done wrong. But I just use DOM tube. I DO need to go the place I get it to find out more about it (the DOM I use). Never had an issue welding it though.

Edit#2. Just called the steel supply and they said ALL thier DOM under 5 inches is 1020 steel. So thats what I am messing with. 

[nvheattreating]

The weld issue is not due to too much heat, but rather too fast of a cooling rate.  One continuous fillet may be better, but it doesn't relate to more or less heat.  The DOM (Drawn Over Mandrel) 1020 tube doesn't have anywhere near the hardenability of the 4130, that's why it is much more forgiving.  It has both low carbon and low alloy content.