tubing size for a-arms?

[TravisB]

Originally Posted by 62fairlane

so what is the problem with 4130 tubing? just by changing to that I could cut the wall thickness in half.

I don't know that there is a problem with chrome moly...maybe companies don't use it because it is more expensive!

[Matt@Lateral Dynamics]

Most guys I've talked to don't use 4130N for weldments because they're scared of welding it. Seriously. It's prone to hot cracking and brittle welds, so they just don't bother. Given the prices of steels now days, 4130N isn't that much more expensive than DOM is.

And.... 1 x .219" wall???? Damn.

[TravisB]

Originally Posted by Matt@RFR

And.... 1 x .219" wall???? Damn.

Ya I know I looked in the book and on the website to make sure but thats what it says......

[62fairlane]

thats why I as looking at LARGE diameter tubing 1.375" since it will handle the bending forces better but have room to go high as 1.5" (I just feel this will be getting TOO big) well using the 1"x.219" tubing as a guide I can run FEA on those then base my tubing size on the strength comparison.

[Musclerodz]

The only advantage to using chromoly over DOM is weight savings due to strength to weight ratio. If weight is not the issue stick with DOM. I use chromoly all the time repairing vintage aircraft but I gas weld it only.

Mike

[62fairlane]

well I only have access to both a TIG and Gas torch. I heard you just shouldn't MIG weld the 4130?

[TravisB]

Originally Posted by 62fairlane

I heard you just shouldn't MIG weld the 4130?

correct the mig welding process makes the 4130 brittle and is more proned to cracking.......

[Kendall Burleson]

Hey guy
You don't want to use 4130 on the street thin wall or heavy wall .4130 will not last very long on the street because memory compare to mild steel .take a one foot peice and bent it and will not bend back to a netural state many time before failure. compared to mile steel DOM have a good memory that is why NASCAR used it in all their rollcage. because went one those 3800lb car flip over and over the cage is still in one piece bend but not broken (DOM mild steel).A NHRA top fuel car crash the chassis will some time break in half because it weight 1900lb (4130 chromemoly) they are looking for lite-weight.you take 11/2x.085x12 long(4130)has more strengh that 11/2x.125x12 long but the 4130 is lighter but it will work harded and break.Indy car will only use 4130 on chassis parts only and small prop air planes. I hope this help you

kendall

[Kendall Burleson]

Hey guy
You don't want to use 4130 on the street thin wall or heavy wall .4130 will not last very long on the street because memory compare to mild steel .take a one foot peice and bent it and will not bend back to a netural state many time before failure. compared to mile steel DOM have a good memory that is why NASCAR used it in all their rollcage. because went one those 3800lb car flip over and over the cage is still in one piece bend but not broken (DOM mild steel).A NHRA top fuel car crash the chassis will some time break in half because it weight 1900lb (4130 chromemoly) they are looking for lite-weight.you take 11/2x.085x12 long(4130)has more strengh that 11/2x.125x12 long but the 4130 is lighter but it will work harded and break.Indy car will only use 4130 on chassis parts only and small prop air planes. you also have to TIG weld 4130 I hope this help you

kendall

[Musclerodz]

Originally Posted by Kendall Burleson

Hey guy
You don't want to use 4130 on the street thin wall or heavy wall .4130 will not last very long on the street because memory compare to mild steel .take a one foot peice and bent it and will not bend back to a netural state many time before failure. compared to mile steel DOM have a good memory that is why NASCAR used it in all their rollcage. because went one those 3800lb car flip over and over the cage is still in one piece bend but not broken (DOM mild steel).A NHRA top fuel car crash the chassis will some time break in half because it weight 1900lb (4130 chromemoly) they are looking for lite-weight.you take 11/2x.085x12 long(4130)has more strengh that 11/2x.125x12 long but the 4130 is lighter but it will work harded and break.Indy car will only use 4130 on chassis parts only and small prop air planes. you also have to TIG weld 4130 I hope this help you

kendall

Kendall, how about some hard facts rather than analogies. First off if either part is bending in a suspension system, it needs to be replaced regardless of what material it was manufactured with. "Memory" in which you are referring to is "how many times can the piece of material be bent with out fatigue cracking". If your a-arm is bending under load, you built it wrong and do not need to be messing with critical systems such as suspensions. The reason NHRA top fuel cars use chromoly and NASCAR doesn't is NASCAR has a minimum weight requirement and teams are usually adding weight to meet weight. If NASCAR teams could run lighter chassis, trust me, they would take full advantage of it. The breakage of a top fuel car cage due to chromoly memory is crap. At 300 mph, DOM will fail too. That is twice the speed of NASCAR, which means about 4 times the impact forces. As stated before, the use of chromoly in a suspension system, roll cage, or any other system or structure is its superior strength to weight over DOM tubing.

DOM tubing is easy to weld and can be welded by MIG, TIG, arc, or gas welded giving good quality welds without any special attention to the welded area. 4130 is not so easy. 4130 tubing is predomitely used in the "N" condition or normalized (untempered). 4130 gas welds easily, but few do it any more. On thicker tubing, usually 1/8" or thicker wall, I prefer to TIG weld. When TIG welding 4130, due to the extreme temperature of a TIG weld, 4130 will harden or heat treat at the weld but the rest of the tube will not. This sets up a stress point at which if given enough force it will crack and fail right next to the weld. Therefore when TIG welding 4130, it is best to use a rosebud torch and PREHEAT the entire area plus a few inches. After TIG welding, POST HEAT the are again plus a few inches to relieve the weld stresses and allowed to air cool. This will bring the entire welded area back to a normalized condition.

Oh....and I work on them small airplanes everyday.

Mike