ill second that notion.......dont leave.........differing opinions help us all.......regardless of those who are intolerant to different views.............ignore the flames, and just continue posting with the people that are happy to learn from you.

 

MG-
I don’t know much about metals or drive trains, but it’s obvious that is not what this thread is about for you. I do a thing or two about social edict.

Ken went back and deleted all the threads regarding your ego, you leaving and you in general to clean this place up. Not so you could get last the word.


I'll stop there before I **** off your lawyer.


Best luck in all your endeavors,
Trey

 

It had better be short and of high-quality material if they're only using 70 mm of diameter with 3.73 gears on a car that'll presumably be capable of 170+ MPH speeds. The wheelbase is only 2" shorter than my Impy, so that puts the driveshaft at maybe 52" center-to-center. With a sub-3" tube diameter and assuming this is a one-piece shaft, you're looking at a critical speed, oh, sub-8K RPM (I didn't run the numbers right now) unless something exotic like MMC or carbon fiber is used. If they used a two-piece shaft, well, then they did the right thing.

Don't know where to get 290 KSI Ti, as the strongest weldable stuff that I'm familar with is the 140 KSI 6Al-4V. It's expensive and difficult to work, which means that you typically can't do anything cool with tubing such as double-butting. This also means that folks are unlikely to spend the time doing detail stuff that they should, like gusseting joints properly. And of course there's the difficulty in properly shielding Ti during welding, which is evident when inspecting something like a Chinese Ti bike frame and observing the white crust around the welds. Really isn't much sense to use the stuff unless you're talking about high-temp use or large-diameter tubing or large sheet structures (as the minimum practical thickness means that you can't exploit it's strength-to-weight ratio when teh structure gets too small), and then you're talking about big fabrication problems, either in simply trying to shield the weld, or finding enough force to form the sheet or tubing. Makes damn good springs, if you've got enough room to package them.

 

heh, I’ve run across tech inspections from 2 separate sanctioning bodies that required you to drill your bar in 2 randomly selected locations in front of the tech inspector to verify tube thickness before the cage would be certified. Strange part, I know of amateur racers that got caught on that.

Now that is pretty slick. Thinking about it, what do you do at the bends? If I was a tech inspector I’d want to see the thickness on the outside of a bend...

you know, I haven’t even been able to find 1026 in any kind of reasonable quantity. Seems like it would be the way to go from a safety standpoint.

Though this is what bugs me about this whole thing. If you built your whole cage out of 1026, under most sanctioning bodies it would be illegal, or with the NHRA on a slower then 7.50 chassis you’d be required to use .118” thickness everywhere where you could use MUCH lighter, .083” or thinner in the same OD if you used 4130, but in either case (even if you used the 4130 wall thicknesses), the 1026 one would be stronger and SAFER. To a lesser extent, if you used the same size 1018 tubing as the 4130, there would be no appreciable difference in strength and you still have a safer cage but it would be illegal.

The only exception I know of is circle track cars. Don’t know about the big boy NASCAR classes, but I know that in the lesser cars pretty much live on mig welded mild steel cages, and I’ve heard references (don’t know first hand) that they are required to use mild steel.

Heh… funny, that’s my brother’s argument why I wouldn’t be able to get anywhere with doing custom stuff full time. I’ve got a tendency to get hung up in making sure that things are as ‘right’ as I can possibly get them within my skills and mostly within the limitations of the tools/equipment that I own, especially from an engineering standpoint. I love the elegant solution, but it almost always takes a little more time.

In the mean time, I’ve tried to take his advice and take the “fug it, lets stick some metal together and get this thing running” attitude on some of the things that I’ve built for him lately. His reaction was “cool, I don’t believe that you got that done so fast, and it still looks better then what most of the ‘pros’ around here would do.” Took the same approach with some welding/custom work that a couple of guys dropped off and got it done in 3 hours vs the 7 or so that I was expecting it to take (and still made more then I ever have in a week at my full time job). Everyone was happy but me… I kept having the “I can’t believe that this piece of crap is what he really wants” thoughts. I guess that most people just don’t understand the difference between ‘done’ and ‘done right.’

(FWIW, I did end up redoing a few things to make myself a little happier with them)

Hum… the original topic was driveshafts? Really?

 

Hum, yea, interesting point… 70mm is about 2.75”… that’s not so big… Denny’s claims my 3.5” MMC shaft has a critical speed of 9600rpm, not that I’ve tested it ;-)

FWIW, I wouldn’t be surprised if the DS is significantly shorter on a car like that, you’d expect it to be designed with as much of the mass toward the center of the car as possible, which should mean that the engine would be mounted further back then in your impy…

hum, makes perfect sense, but I’ve never thought about it that way. That raises a second question: why did GM go with a 2 piece on the v6 f-bodies and a single on the v8’s?

It’s easy to weld, just do it in an inert gas chamber. I’m not sure that I’d go as far as you did on where it makes sense to use since even most of those applications you still run into the issue of it’s tendency to crack at any flaw… not something that can be easily tolerated on a race car, that could get pelted with gravel/debris, sometimes accidentally scratched while being torn down or assorted road rash.

 

Heh heh - actually won't be that tough to do, if you're running something like 4.56s with short (<26") tires.

I wouldn't be so sure of that - the powertrain actually sits fairly far back in a B-body, although it's still in a different ZIP code than the rear axle



Two-piece shafts aren't uncommon in European cars which are intended to spend most of their life above 100 MPH, but I'm really surprised that GM used on on the V6 F-body (I've never really checked one out that closely). Weird.

Most bike frames are done using an argon purge - simply flood the inside of the tube with inert gas and use a monsterous gas cup on the torch. That gets expensive real quick-like, which is one reason that these are so expensive (disproportionally so relative to material cost).

I didn't think Ti was all that bad with regards to notch sensitivity, but regardless - it's very difficult to notch it in a real-world situation. I'm by far an expert in using Ti, but I wouldn't be surprised if it's greatly influenced by contamination during the processing of the material or fabrication of the part. I certainly wouldn't worry much about a part getting accidentally scratched, but I could see a road-rash concern in certain cases (although I've yet to see a Ti bike frame taken out of service due to scarring).

 

 

Just coming from a youngn' by-stander who likes to read and learn a lot (which btw i feel i do learn from time to time in this forum) that i dont think it's a matter of most people "understanding" 'done' and 'done right' but more of an issue of when that difference of 'done' and 'done right' is going to be that LARGE of an issue to warrant a problem of some sort.

I think that makes sense, maybe i can conjure up an example if i think hard enough. Give me a little time when i'm more awake and maybe i can (i'm recovering from two visits to the hospital within a day with 106.3 and 105.8 fevers)