CM tubes are smaller in diameter

There's is a tube gauge you can buy.

 

Tubing is same size , 1 5/8 for cages 1 3/4 for roll bars. Sonic tester would be only way I'd know to verify thickness..... .083cm, .120mild steel.

 

Tubing is same size , 1 5/8 for cages 1 3/4 for roll bars. Sonic tester would be only way I'd know to verify thickness..... .083cm, .120mild steel.

This. I will add if you know what you are listening for the two will make a different tone when tapping on them but the above is truly the best.

 

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That's why anyone with sense get's the highest sticker they can when selling a car!!!
You can state what it is and have proof.

Unless of course you are a POS like that jeff lutz thief and just bribe a guy to get any sticker you want!!!!


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My chassis builder verified my chassis as being CM with an outside diameter tool. He's also does IHRA chassis cetifications.

 

Neat car! But that's not possible. The outside is exactly the same size.

 

I think this was a question on a chassis engineering test.

Answer:
Select a tube at random.
Measure tube diameter with vernier calipers.
Drill hole in tube.
Insert depth gauge.
Measure depth to opposite inside of hole.
Subtract measurement from tube diameter.
Difference should be approximate thickness of tube.
Fill hole with caulk, JB Weld or real weld, depending on if you are buying the chassis.
If not buying leave hole for next shopper!

If you can't afford a depth gauge you can make one from a piece of wire or just mark the drill bit shank with a piece if tape as it touches the inside opposite the hole. But if you can't afford the depth gauge perhaps you are getting in over your head!

 

You can tell high chromium content alloys from mild steel with a drop of strong nitric or sulfuric acid. The lower the chromium content, the more fizzing, as iron atoms that are not surrounded by chromium atoms react with the acid, forming an iron salt and releasing hydrogen gas (fizzing). If you use nitric acid, brown fumes will rise from mild steel. High chromium content alloys exhibit no fizzing and, if using nitric acid, no brown fumes.

 

This is the only way mentioned in this thread that will actually tell you if its 4130 or MS

Measuring the bar thickness and dia is nice, but I could use MS, build a chassis to CM spec, and using the methods you all mentioned you all would think it was CM

 

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IIRC, some guys do use 1 3/4 mild "OR" 1 5/8???

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Negative

 

Simple. Get your OD, drill a small hole in the center of the tube , use a piece of welding wire and see how much goes in. Do the math and get the wall thickness. That's how I verified my own.

 

Isn't it also possible to grind it and judge by the Sparks?
Don't know if any seller is gonna let someone grind it or put acid on it though!

 

I'm pretty sure NHRA chassis inspectors use the acid test.

A couple things most people don't realize:
1) 4130 is NOT lighter than 1018 or 1020. They have nearly identical densities. 4130 has a higher yield strength, so thinner wall tubing can be used for weight savings.

2) 4130 will deflect as much as 1018 or 1020 having the same section and loading conditions. Because 4130 has a higher Sy, it will take higher loading and deflect more before yielding. This is why 4130 is commonly referred to as "springy".

 

The NHRA tech guy that certified my chassis to 6.00 used tubing diameter templates and ultrasonic wall thickness to verify it was cm, according to him, dom does NOT come in the same wall thickness as cm.

 

A few of these guys thinks it does. But don't ask me, I don't know for sure. So, I'm not going to make a comment about it.

 

I would take it to a NHRA chassis inspector, they will ultrasonic the thickness. Also if the welds looks like they were TIG welded, that is likely 4130 Chromoly. Any other welding technique is not suitable or allowed by SFI (even though professionals weld chromoly boiler tubing with stick all the time). If you look on the chassis there will be some tiny little holes already drilled in the tubing to vent air while you are welding. Some shops will cover these up, but there is so many that likely there is still a few left.

Also NHRA inspectors only focus on the area surrounding the driver, fwd of the firewall and aft of the funny car cage they don't car about. That is where you should be the most worried about wall thickness. There is a chassis company, Zeeker I believe, that used tubing that was too thin when bent and they went out of business as a result. Check in the bends for some insight.

 

My very 1st inspection, the inspector sanded off a spot of my new paint and applied a chemical, acid or what ever. I assume, to prove CM.

Re certs never did that.

 

There is so much bad info in here it's ridiculous. Caveat Emptor.

 

You can tell using a prick punch or a file

 

4130 sounds different and a slight tap with a sharp punch will tell you what it is in most cases.

 

The internet is interesting. Scads of opinion presented as fact. When you aren't sure of something, qualify your statement so others aren't mislead by it.

 

Since we have some folks in here that know chassis work.......

On an average size drag car, how much cost difference is there between a MS build, and a CM build?

 

Material cost? Labor? Rollcage? Full chassis?

 

the cost of the tubing is one thing, the cost of TIG welding Moly vs MIG welding MS is far more massive.

I TIG Tacked my Moly chassis after a month of cutting,notching fitting the moly tubing, the thinner tubing must be cut slower in a endmill style knotcher to prevent it catching and bending the ends, so that adds up as well.

I took my chassis to the local chassis shop, 36 hours of TIG welding at 75 dollars an hour, we brought it back home and started welding in the steel floors and firewall, another 20 some hours of TIG welding.

Mild steel? we used to weld up a whole dirt track stock car kit in a couple of nights after work...

there is a reason why RJ Race cars sells the kit I bought unwelded for a bit over 2 grand, but welded its 7500...

http://i37.photobucket.com/albums/e92/blizzardND/Maverick 2016/20160124_203508_zps4xulplnr.jpg

 

sorry wrong picture, ment for this one.. damn 5 minute edit rule here..

 

If you build a car using mild steel you might as well plan on either not ever selling it, or almost give it away if you try to sell it.

 

Every time I've had my stuff recertified the inspector used a sonic tester for the wall thickness and a small portable hardness tester to check the material type.

 

What did the tester look like? Was it a C-clamp type deal?

 

General rule of thumb just as a reference and in no way 100% accurate would be to see if it is Tig welded or Mig welded. Anyone building a mild steel chassis probably will not take time to Tig weld it or they may not have the skill set.

 

That is completely wrong.
There is tons of mild cars just in this area that are TIG'd.
Plenty of guys built S/G kits and TIG'd them.
I also hang at different chassis shops, and they TIG everything, mild or moly.


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I understand, but that is way to iffy to even consider.
If I've seen many just around here, country wide it's impossible to even guess how many mild cars are TIG'd.
Like I said, those S/G kits were huge and most were probably MIG'd, but many were not.


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This day and age I can't goat him why anyone would bother with MS.