Re: moly or mildsteel cage?
[Re: Pleaz]
#169634
12/18/08 09:59 AM
12/18/08 09:59 AM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,219
New York
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And still this question is raised.
No, moly is not more rigid than mild steel. The elasticity of all steel alloys is almost identical (Young's modulus: 30 × 10^6 psi).
"I have always heard that moly is twice as light, and twice as strong." No, moly is not lighter than mild steel, the weight difference is only 1-2% depending on the exact alloy. The reason it's lighter is smaller wall thickness - that's it. No, moly is not twice as strong, it's about 30% stronger (not stiffer), and that's if properly welded and heat-treated. If the wall thickness is reduced to save weight the strenghs are about equal. You can have more strength with the same weight, the same strength with less weight, or some intermediate.
Re: "they don't want them trying to weld chrome moly with a OX Acetelene torch" Guess how Reynolds 531 chrome-moly chassis (including Formula 1 back in the day) are built for road racing? That's right - gas brazed with a torch. Read Carroll Smith.
"both these mild steel cages deflected WAY too much for safety" That's not what did it.
Boffin Emeritus
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Re: moly or mildsteel cage?
[Re: polyspheric]
#169635
12/18/08 10:35 AM
12/18/08 10:35 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
And still this question is raised.
No, moly is not more rigid than mild steel. The elasticity of all steel alloys is almost identical (Young's modulus: 30 × 10^6 psi).
"I have always heard that moly is twice as light, and twice as strong." No, moly is not lighter than mild steel, the weight difference is only 1-2% depending on the exact alloy. The reason it's lighter is smaller wall thickness - that's it. No, moly is not twice as strong, it's about 30% stronger (not stiffer), and that's if properly welded and heat-treated. If the wall thickness is reduced to save weight the strenghs are about equal. You can have more strength with the same weight, the same strength with less weight, or some intermediate.
Re: "they don't want them trying to weld chrome moly with a OX Acetelene torch" Guess how Reynolds 531 chrome-moly chassis (including Formula 1 back in the day) are built for road racing? That's right - gas brazed with a torch. Read Carroll Smith.
"both these mild steel cages deflected WAY too much for safety" That's not what did it.
And why do you say its not stiffer, it takes a significantly greater force to bend it on a bender over the mild steel?
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Re: moly or mildsteel cage?
[Re: LA360]
#169636
12/18/08 10:43 AM
12/18/08 10:43 AM
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Joined: Mar 2006
Posts: 9,910 Eighty Four, PA
B G Racing
master
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master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
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From your first picture it is a prime example of improper installation.The piller bar is layed back way too far and is attached at the side of the halow bar.It should be attached at the underside of the halow to give any support.Many times an installer will try and follow the windshield and body contours which make the angles less effective for support.NASCAR uses MS cages for impact absorption(give)CM is lighter and harder and has little impact absorption quality.CM is more prone to break rather than bend.And because of it's hardness it will fatigue from twisting and loading in time.This is why prostock,top fuel and other classes constantly update their chassis.If you have ever seen a CM Chassis wrecked you will commonly see tubing breaking not at the welds but in the tube body.And also a good oxy/ecty welder can weld CM just as good as a good tig welder.A furthur note,with all the approved and new welding techniques CM can be mig welded to perfection,NHRA just doesn't allow it.They fear that that fitment would be compromised buy the ease of application of mig welding,where as you can't very well hide gaps with the tig process.Structural design, effectivness,fitment,weld and application are all important part of how you choose material and build a cage or chassis.
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Re: moly or mildsteel cage?
[Re: B G Racing]
#169640
12/18/08 01:41 PM
12/18/08 01:41 PM
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Joined: Aug 2006
Posts: 290 Cincinnati, Ohio
d7cook
enthusiast
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enthusiast
Joined: Aug 2006
Posts: 290
Cincinnati, Ohio
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Another big difference is one car has a funny car cage and one doesn't. The FC adds a lot of strength. On my car the pillar bar hits the side of the halo but another bar triangulates from the front of the halo to the pillar. I agree the car that squashed was poor design. I don't think a CM roll bar will suffer too much from cracks but a full CM chassis car will usually require crack repair at the end of every season. Quote:
From your first picture it is a prime example of improper installation.The piller bar is layed back way too far and is attached at the side of the halow bar.It should be attached at the underside of the halow to give any support.Many times an installer will try and follow the windshield and body contours which make the angles less effective for support.NASCAR uses MS cages for impact absorption(give)CM is lighter and harder and has little impact absorption quality.CM is more prone to break rather than bend.And because of it's hardness it will fatigue from twisting and loading in time.This is why prostock,top fuel and other classes constantly update their chassis.If you have ever seen a CM Chassis wrecked you will commonly see tubing breaking not at the welds but in the tube body.And also a good oxy/ecty welder can weld CM just as good as a good tig welder.A furthur note,with all the approved and new welding techniques CM can be mig welded to perfection,NHRA just doesn't allow it.They fear that that fitment would be compromised buy the ease of application of mig welding,where as you can't very well hide gaps with the tig process.Structural design, effectivness,fitment,weld and application are all important part of how you choose material and build a cage or chassis.
1967 Coronet, 1989 Daytona tube chassis.
Former cars, 66 Charger, 67 R/T, 69 Coronet, 67 Dart GT.
-Banned for life from V8Buick.com-
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Re: moly or mildsteel cage?
[Re: PS Arrow]
#169646
12/18/08 06:46 PM
12/18/08 06:46 PM
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Joined: Dec 2006
Posts: 2,137 Byron, NY
W.I.N. Racing
top fuel
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top fuel
Joined: Dec 2006
Posts: 2,137
Byron, NY
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BG and polyspheric Great job in properly explaining the "CM/MS Myth's"
'01 P1500, Blown/Inj BAE,/Veney ,Bruno/CS2,Dana 60 '01 Dodge 3500 S Cummins Auto, Fresh air kit, 4" Exhaust, '05 Dodge Magnum R/T - Too Much to list '60 Willys CJ5 '01 International LPX - Project,DT466, Allison '64 Plymouth Valiant, Inj 528 Hemi, 2spd
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Re: moly or mildsteel cage?
[Re: W.I.N. Racing]
#169647
12/18/08 06:48 PM
12/18/08 06:48 PM
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Joined: Jan 2003
Posts: 32,394
Quicktree
I Win
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I Win
Joined: Jan 2003
Posts: 32,394
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Quote:
BG and polyspheric Great job in properly explaining the "CM/MS Myth's"
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Re: moly or mildsteel cage?
[Re: MR_P_BODY]
#169649
12/18/08 08:18 PM
12/18/08 08:18 PM
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Joined: Jan 2005
Posts: 3,639 Oakland, MI
dizuster
master
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master
Joined: Jan 2005
Posts: 3,639
Oakland, MI
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[quote} And why do you say its not stiffer, it takes a significantly greater force to bend it on a bender over the mild steel?
Excellent question. Chassis stiffness is a lot different then impact stiffness. During chassis stiffness, the cars chassis/cage don't bend far enough to take a permanent bent shape. The metal is still in it's elastic state, and returns to it's original shape after it's loaded. But a CM car as outlined above uses thinner material, so it automatically looses stiffness. The metal itself if they were both the same thickness would bend elastically in the exact same way.
The advantage to your point of CM, in an extreame case like a crash, the bars often bend past their elastic point. This is where CM is material superior. But like I mentioned above, the wall thickness pretty much negates the material property benifits. But to your point when greatly bending CM (like bending a roll cage), you can feel that extra effort to bend the CM. Specific material has a lot to do with it though. I know my DOM mild steel was an absolute pain in the a... to bend, more so then the CM that I've done...
So with MS you get a heavy rigid chassis when compaired to a CM lighter more flimsy chassis...
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Re: moly or mildsteel cage?
[Re: dizuster]
#169650
12/18/08 08:35 PM
12/18/08 08:35 PM
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Joined: Nov 2004
Posts: 6,890 North Alabama
Monte_Smith
master
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master
Joined: Nov 2004
Posts: 6,890
North Alabama
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You brought up DOM tubing, problem is, 90% of people who use MS don't use DOM, they use cheap, welded seam MS. A well built DOM cage is as strong as anything else and DOM costs nearly the same as Moly. I personally used DOM on all my MS cages, but when I got to the point that I no longer MIG welded any cage, regardless of material, it made no sense to not use Moly. Makes the car lighter and worth more for resale. I don't care what the cert is, a Moly car will always bring more. I would not put MS in a new car period, but that's just me.
Monte
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Re: moly or mildsteel cage?
[Re: Monte_Smith]
#169651
12/19/08 10:44 AM
12/19/08 10:44 AM
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Joined: Mar 2006
Posts: 9,910 Eighty Four, PA
B G Racing
master
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master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
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Quote:
You brought up DOM tubing, problem is, 90% of people who use MS don't use DOM, they use cheap, welded seam MS. A well built DOM cage is as strong as anything else and DOM costs nearly the same as Moly. I personally used DOM on all my MS cages, but when I got to the point that I no longer MIG welded any cage, regardless of material, it made no sense to not use Moly. Makes the car lighter and worth more for resale. I don't care what the cert is, a Moly car will always bring more. I would not put MS in a new car period, but that's just me.
Monte
The cost of DOM(drawn on a mandral)MS to Aircraft quality CM is 1&1/2 times cheaper,we buy direct.Rolled and seamed MS is the cheapest tubing available.There are many different quality specs for either,varying the cost.We use DOM-MS and AC-CM for our custom chassis and cage work.We don't push our customer either way,we educate them on the pros and cons for their particular application and cost budget.We let them decide.Our 68 Cuda dbl rail/strut chassis car and our 65 Dodge a-arm car are both MS.We have 5 cars in the shop for up-grades,of the 5 three are MS and 2 are CM.4 of them are certified to 7.50.Go figure?
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