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Old 09-01-2010, 05:21 PM   #1
OUScooby
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Default What type of steel to use for a custom subframe?

Just wondering what type of steel to use for a subframe? What diameter and thickness of steel tube is recommended?

Oh and if anyone has pics of their subframe to share, feel free to post them here.
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Old 09-23-2010, 07:56 PM   #2
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I'll bump this for you hoping to maybe get a response from someone who knows.
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Old 09-23-2010, 08:43 PM   #3
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Just a guess. But I would use 1" Dom steel such as roll bar material
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Old 09-23-2010, 09:23 PM   #4
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I guess it would depend on what you want to do.
If its for full on gravel racing events then you would want to use a heavier wall thickness. Tarmac could me made lighter,road so on.
Commonly chrome moly is used in about 1" Dont know about the wall thickness.
I would think a seamless tube would be the go. I have heard of cold drawn and hot but I dont know what the properties are.
Maybe google roll cages and suspension parts for some clues as to what steel they use.
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Old 09-24-2010, 04:58 AM   #5
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I would personally suggest aluminum (maybe thats because I work at an aluminum fab plant). It is considerably lighter, and you won't be seeing any temps that could make it bend.

Then this is all assuming that you weld aluminum, I would suggest taking your time with a nice tig for something like this.

Because aluminum is lighter you could can get pretty thick side walls.

I made a wakeboard tower out of 2" OD 1/8" wall tube and it towed two boarders and some people on it at the same time. I know this doesn't apply too much to your situation, but I am just saying that it will definitely be strong enough. For your situation you could go with something like .75" or 1" outer diameter. Here is a good site:http://www.onlinemetals.com/merchant.cfm?step=2&id=71

I would suggest drawing or modeling the piece you are going to make before purchasing any material. If you have dimensions I can see if I can make a piece and hopefully even stress test it (this is what I do as my job in the summers).

Last edited by boardinshorty81; 09-24-2010 at 05:08 AM.
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Old 09-24-2010, 02:05 PM   #6
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Thanks for the help.

I am going to be making a solar car at school and I need to learn how to weld aluminum. I figured I might as well try and make some sub-frame braces while I have a bunch of cool tools to use.
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Old 09-24-2010, 03:16 PM   #7
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Quote:
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Thanks for the help.

I am going to be making a solar car at school and I need to learn how to weld aluminum. I figured I might as well try and make some sub-frame braces while I have a bunch of cool tools to use.
I do the same but for our fsae car. The car is good practice for tuning too.

I love college, there are plenty of free ways to get experience in groups and such.
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Old 09-24-2010, 06:35 PM   #8
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I do the same but for our fsae car. The car is good practice for tuning too.

I love college, there are plenty of free ways to get experience in groups and such.

Totally agree. Sometimes I get annoyed working with computer geeks though. EE is filled with these total nerds. Smart as hell but not very good with their hands.

This will be my first venture into the welding world.
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Old 09-25-2010, 05:00 AM   #9
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EE is filled with these total nerds. Smart as hell but not very good with their hands.
Yeah I walk this fine line. I always come back to working with my hands because I have something to hold after.

Where are you intending on having the support mount under the car?
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Old 09-25-2010, 11:55 AM   #10
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Well I was thinking about making some fender cowl braces. Maybe some rear subframe bracing as well. In my wagon I get a lot of looseness on the rear tires. Welding aluminum does not look that easy. So maybe my dreams overstepped reality again.

I am attending UNM. What school are you attending bordinshorty81?
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Old 09-26-2010, 02:44 AM   #11
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Quote:
Originally Posted by oguitar

I am attending UNM. What school are you attending bordinshorty81?
I am at case western reserve in Cleveland. I hope to get some aluminum welding practice sometime next month, I'll see how long it takes me to pick up (to the point of making a brace of some sort. I am actually going to try to help weld the frame for the schools fsae car, that should give me some structural practice.
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Old 09-26-2010, 02:49 AM   #12
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So aluminum is the metal to use for a subframe? If I do a subframe I won't be fabricating it myself, I have zero metal working skills. What would be wrong with using steel, it would be cheaper, and even though there would be a weight penalty it would at the lowest point on the car, if it ways less than the stock subframe you still save weight, if it weighs more than you are lowering the center of gravity on the car.
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Old 09-27-2010, 10:42 AM   #13
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how has 4130 not been mentioned? I would't bet Al for a rear subframe
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Old 09-27-2010, 01:18 PM   #14
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Quote:
Originally Posted by OUScooby
So aluminum is the metal to use for a subframe? If I do a subframe I won't be fabricating it myself, I have zero metal working skills. What would be wrong with using steel, it would be cheaper, and even though there would be a weight penalty it would at the lowest point on the car, if it ways less than the stock subframe you still save weight, if it weighs more than you are lowering the center of gravity on the car.
Not necessarily. You have to think of what kinds of loads you will get in each direction. Saying aluminum will work doesn't mean much as it will work with the right shape, but if designed poorly it will bend as will most metals.
I just despise of steel because of it's weight, that does not mean it isn't right for your application. I would wait for someone with some experience making a brace to chime in with the magnitude of loads you will be looking at.
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Old 09-27-2010, 02:15 PM   #15
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Easy one: 4130 aka chrome-moly aka t45. It is what all race car roll cages and subframes are made out of. It has an infinite fatigue life (unlike aluminum) if properly designed and can be made nearly as lightweight as aluminum. Look up MSI's subframes. Common diameters are .75"-1.5" and wall thicknesses of 0.049"-0.095".

Last edited by bigusnickus; 09-27-2010 at 02:18 PM. Reason: gave wall thickness and diameters
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Old 10-02-2010, 03:23 PM   #16
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Quote:
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how has 4130 not been mentioned? I would't bet Al for a rear subframe
It was mentioned in post #4
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Old 10-02-2010, 03:26 PM   #17
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Quote:
Originally Posted by bigusnickus View Post
Easy one: 4130 aka chrome-moly aka t45. It is what all race car roll cages and subframes are made out of. It has an infinite fatigue life (unlike aluminum) if properly designed and can be made nearly as lightweight as aluminum. Look up MSI's subframes. Common diameters are .75"-1.5" and wall thicknesses of 0.049"-0.095".
No, 4130 isn't what ALL race car roll cages and subframes are made out of. MOST of them are made out of DOM which stands for Drawn Over Mandrel for those of you who don't know. 4130 is used by racers that can AFFORD it.
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Old 10-04-2010, 07:39 PM   #18
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No, 4130 isn't what ALL race car roll cages and subframes are made out of. MOST of them are made out of DOM which stands for Drawn Over Mandrel for those of you who don't know. 4130 is used by racers that can AFFORD it.
DOM is a manufacturing process, not a steel grade.

4130 is DOM. The least expenisve DOM grade is a plain carbon steel such as ASTM 1018 or 1020, which would also work exceptionally well in this application. I guess I am just used to 4130 because you can realize a weight savings over plain carbon by decreasing the wall thickness due to the higher strength of the material.

Either way, steel tubing would be your best choice, preferrably a DOM or seamless tube.
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Old 10-04-2010, 08:28 PM   #19
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I would not use aluminum in this application without a post-weld heat treatment.

T-0 aluminum is pretty much junk. It looks nice and won't corrode, but it will be much heavier than steel for the same structure if both are well designed.

6061 T-651 aluminum would be a great material for a subframe, lighter and stronger than steel. Stiffness is all in the design and could be made equal with either material.

If you do use aluminum, take care to make sure your bolt hole surfaces are thick enough to handle the impact forces they will be seeing without ovalizing.

I would use 4130 steel myself.
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Old 11-07-2010, 01:00 PM   #20
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Just to clear things up, 4130 is NOT T45. 4130 is not accepted by may sancioning bodies due to how brittle it gets in the HAZ.. The only way to solve that problem is to normalize the material. Since there is really no way to prove the joints have been normalized. You cannot use it.

T45 is Carbon Manganese Steel. You cant even buy it in the US and the only place that I have seen it being used is in FIA Homoligated roll cages. AKA Custom Cages UK. Its got around the same tensile strength as 4130 but its properties dont change with heat.. meaning you can even MIG weld it..

Save some money and make your subframes out of DOM 1020. Use 1" x .080". Design it well.

Quote:
Originally Posted by bigusnickus View Post
Easy one: 4130 aka chrome-moly aka t45. It is what all race car roll cages and subframes are made out of. It has an infinite fatigue life (unlike aluminum) if properly designed and can be made nearly as lightweight as aluminum. Look up MSI's subframes. Common diameters are .75"-1.5" and wall thicknesses of 0.049"-0.095".
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Old 11-07-2010, 03:06 PM   #21
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Just to clear things up, 4130 is NOT T45. 4130 is not accepted by may sancioning bodies due to how brittle it gets in the HAZ.. The only way to solve that problem is to normalize the material. Since there is really no way to prove the joints have been normalized. You cannot use it.

T45 is Carbon Manganese Steel. You cant even buy it in the US and the only place that I have seen it being used is in FIA Homoligated roll cages. AKA Custom Cages UK. Its got around the same tensile strength as 4130 but its properties dont change with heat.. meaning you can even MIG weld it..

Save some money and make your subframes out of DOM 1020. Use 1" x .080". Design it well.
Looking at the differences between 4130 and 1020 (price and strength) I may change my mind from my previous statement. Properly designed with appropriate safety factors, the part made with 1020 will only be about 10% heavier. A properly designed subframe will weigh around 15 lbs, that's only a difference of 1.5 lbs. Not a big deal in my book for the cost and hassle.

I'll probably still go with 4130 for my stuff, but will more seriously consider 1020 as a good option.
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Old 11-07-2010, 04:23 PM   #22
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Double post
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Old 11-11-2010, 02:25 AM   #23
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Quote:
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I would not use aluminum in this application without a post-weld heat treatment.

T-0 aluminum is pretty much junk. It looks nice and won't corrode, but it will be much heavier than steel for the same structure if both are well designed.

6061 T-651 aluminum would be a great material for a subframe, lighter and stronger than steel. Stiffness is all in the design and could be made equal with either material.

If you do use aluminum, take care to make sure your bolt hole surfaces are thick enough to handle the impact forces they will be seeing without ovalizing.

I would use 4130 steel myself.
No.

Tensile strength is only 45000 psi.

Mild steel starts in the 60000 psi range.

You may be thinking of 7075-T6.
83000 psi tensile strength. But it is not considered to be weldable.
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Old 11-13-2010, 02:28 AM   #24
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No.

Tensile strength is only 45000 psi.

Mild steel starts in the 60000 psi range.

You may be thinking of 7075-T6.
83000 psi tensile strength. But it is not considered to be weldable.
I was thinking of A36 steel and comparing based on yield strength. After a material starts yielding it's pretty much over.

What I meant was that it has a better strength to weight ratio, and I worded it poorly.
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Old 11-15-2010, 12:47 AM   #25
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Hey Justin just saw this. I know what your plaining. So my suggestion is go with the 4130. Mine has a dent in the tubing where I hit something pretty hard. Aluminum wouldn't take as much punishment I would think, but depends on the grade. I have some other idea's if you want to chat some more. Maybe I will have the idea's added to my own.
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