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Old 03-17-2004, 09:32 PM
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Welding Chrome Moly

I just figured out that my new race car has a .095 Chrome Moly chassis. This is good because they are light yet really stiff and resistant to cracking. Now for the problem. I've never welded Chrome moly before and I hear it's a little different to weld on than the tubing I'm used too. I need to lower the top door bar two inches for Tech. Since this is a driver health concern I don't want to go into this without Some knowledge of welding this stuff. I hope someone can explain what I gotta do to keep form being killed should I get hit, or should I say, when, I take hit in the drivers door.

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Old 03-18-2004, 06:49 PM
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You can use mild steel welding rod if you aren't going to heat treat the assy later. The weld must be done with TIG or gas, I prefer TIG but gas is easier to do. If the original welds are 4130 you are going to have to weld with 4130 rods and post heat treat with a torch. This is a specific process and the metal must be polished in between welding and heat treat with the flame so you can see the color change. You must weld 4130 indoors or in a heated area with still air, the cool down phase is important too.

It is important to find out if your frame was welded with 4130 rod or mild steel, many cars are 1010 mild steel welds but all aircraft frames are 4130 welds. Ultimate weld strength doubles with 4130 welds done on 4130 tubing with proper post weld heat treat compared to mild steel. The heat treat is easy to do, you only need an Oxy/Acetylene torch and big tip. Consult your welding rod supplier for specific temps and heat treat times at temp.

Racing regs vary widely on what is recommended but for the drivers cage do the welds with 4130 weld rod and do the heat treat, it might save his life.

Here are some resources but any welders supply has the rods you need, I like Certanium Alloys made by "Premier" but I couldn't find a link online...sorry.

http://www.tinmantech.com/html/kits_4130.html
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Old 03-24-2004, 07:34 AM
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Thanks Chuck for the information. Due to my inexperience with welding rod/Oxy technique I think I'll be farming out the work to a competent shop. It's currently not known what kind of moly the cage is from. I don't believe all of it is either. It's expensive stuff to be constructing an entire car from it. I'm trying to find the original builder. I'd love to learn and practice but not on door bars. Steve Payne hit a guy last year in the door. The door bar broke and stabbed the spun driver through the gut. Not a pretty sight. There are several welding shops in this area so no doubt in finding one who won't charge an arm and a leg.
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Old 03-24-2004, 11:20 AM
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I found the original builder he say's the car was made from 4130 and completely MIG welded. Now This goes back to what I thought I knew about 4130. If it's pre heated with a smokeless flame and slow cooling of the joint the carbon will not build up as easily and make the parent metal brittle next to the bead. According to the builder, it's a much bigger problem in aircraft because the walls are thinner, .030 to .050 instead of the race cars needing .095 to .120. The joint don't cool as fast. Now who is right???? Welcome any comment's.
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Old 03-30-2004, 12:36 PM
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Try Lincoln welding or Miller's websites. Go to FAQ sections or ask them. I'm sure they have had the question a ton of times.
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Old 03-30-2004, 10:17 PM
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welding "moly"

Having built a bunch of moly frame race cars and welded on a lot more and made a good living at one time TIG welding I think that trying to "heat treat" by eyeball with a torch is just a guess at best. Keep in mind that real heat treating is done in a very controled situation...ie even heating and cooling , very precisely monitored temperatures and sometimes a controled atmosphere just to name a few things that happen.. Probably the best you can do is to preheat to some temp that is too hot to hold but not hot enough to boil spit. This will take the chill off cold metal but in reality it will only be about 50 to 75 degrees over a cool garage temp. ( 140 deg F is dam hot). A light sanding of the joint parts with a fresh disc will give you a clean weld area and a quick wipe down with acetone will get rid of most of the oil from your hands. There are several good books at the book store...Performance welding is one. Read them. Most of the hotrod welding is .060 to .188 thickness with 1/4" material being a bit uncommon e xcept the street rods. Welding thin to thick (.060 to .25) I would grind it clean, preheat a bit and have at it. Be sure you use the post flow gas to cool the weld so it cools in an inert atmosphere. Welding is a bit of an art form and it does require a steady hand. Good luck
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Old 04-01-2004, 08:24 AM
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Thanks all
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Old 04-01-2004, 04:18 PM
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If you wanted to get scientific you can use temp sticks to determine what your heat treat temp is. Many aircraft tube frames are field repaired in this manner.

Good Luck Johnsongrass.
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Old 04-01-2004, 05:02 PM
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It was MIG welded? I have always been told that will not last on race cars either. I have a friend who does some chassis fab including full moly rail cars. He says that MIG welds on moly tube will break......might hold for a while, but not too long.

Just what I was told.

Chris
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Old 04-01-2004, 06:44 PM
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http://www.rawlinsbrothers.org/bhfaq/bhweld1.html.
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Old 04-07-2004, 03:28 PM
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TurboS10...Yep that's what he said. Say's he does them all that way. Two of his cars are still winning out of the six he's built. I've always thought the same as you. He wouldn't tell me what he secret was.

Chucky...Saw the same article before. Good reading. Although it does say you can weld chrome moly with a MIG the author doesn't really explain the details well. He only say's that heating after the MIG weld would be a better idea to normalize the carbon. I still like to see someone. I think I'm, gonna post a few pics of the welds. So someone can see what I'm referring to.
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