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Old 09-01-2007, 02:40 AM
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chrome moly roll cage

hello to all..
how can I tell if I have a chrome moly or mild steel roll cage in my car??
and...how can I tell what the thickness of my roll cage is if I have no exposed ends??
thanks..U.D.

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Old 09-01-2007, 02:53 AM
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Well uncle dave, DOM Molly has no seam so if there is no seam line you could have a molly cage. But DOM steel is also (drawn over mandrel) and it has no seam either. The good news is both of these products are plenty strong for a cage application unless a racing orginazition requires moly. Moly tends to be a little darker in color but not always. Ive been buying German made moly and it is very light in color. I build Offroad Racing Frames, and for years we had to drill a hole in the frame so the SCORE officials could look in and measure the thickness. Now days he has an ultrasound device that reads the restance of the metal and thus the thickness of the tube.

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Old 09-01-2007, 08:27 AM
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I know NHRA requires different minimum wall thicknesses for carbon steel and chrome moly.

If you have to know for sure, check with companies that x-ray pressure vessels. Around here, most of them also perform positive material identification. PMI is a non destructive test which shoots x-rays into the metal and then reads the way the "reflect" to determine what atoms are present and in what percentage. You will have to check with them if they can and are willing to do your cage. They will give you a reader sheet with the results. Does not take the place of a material test report, but if you just need to determine if it is chrome moly or not, this should do it for you.
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Old 09-05-2007, 01:49 PM
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If you have a very clean grinding wheel on a bench grinder and some clean samples you can do a spark test. It is still very tough tell even from this. Mild steel has a red spark with few bright stars and molly will be somewhat brighter and more bright stars. It's still hard and even experts can be fooled. I do it side by side then have someone switch samples. I miss about 25% so I'm only a bit above guessing. haha.

On a bare unblasted chassis moly is smooth and a slight OD green gray where mild steel will more black gray. Drill a 3/16 hole with a slightly dull bit and you can tell right away. You might be lucky just to get thru molly where mild steel you can "wear" it thru.
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