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Discussion Starter · #1 ·
gonna be building some lower control arms soon. I want to use 4130 tube, probably 2 pieces of .120 wall, one sleeved over the other. Can I use a regular 3/4-16 tap to thread the inside of the inner piece for my heims, or do i need a weird kind of tap for Chro-Mo?? I don't want to do weld in bungs, because they would be the weak part of the arm, and the weld would not be as strong as the material around it, and I'd have to pay to have it heat-treated and i'm a poor bastard...
 

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A standard tap will work for cromo. Am I catching this right? You want to tap a 3/4-16 thru only 0.24 material thickness? That's only 3.8 threads of engagement minus the boogered up ones from hand tapping. You'll want around 1.5 times the thread diameter as a rule of thumb for the engagement.


[edit: Head was up my ass. Thinking of something totally different]
 

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Elf if you use the proper Mig wire or welding rod the weld will be stronger than the cromo, the tube will theoretically fail first. That of course is assuming the welding is performed by an experienced welder.

IMO the sleeved tube with a welded bung would be stronger than tapping .120 wall 4130. But hey what do i know I am just a dumb fawking hill billy:flipoff2:
 

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They make a higher yield MIG wire, we used to use some 100+ kpsi at the fab shop i used to work at, i think the highest we had was 130, mainly on large trusses, crane repairs, a lot of Mine equipment requires higher yeild strengths on the wire. It wasnt that much more expensive than standard 70-90 wire. Maybe check out the Lincoln site.


If you are worried about the threaded insert failing, why not get some machined out of 4340 to match the tube. This way the wall thickness isnt reduced like with tapping. Then the weak link would most likely be the bracket on the axle housing or the heim/johnny joint.
 

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elf_cruiser said:
gonna be building some lower control arms soon. I want to use 4130 tube, probably 2 pieces of .120 wall, one sleeved over the other. Can I use a regular 3/4-16 tap to thread the inside of the inner piece for my heims, or do i need a weird kind of tap for Chro-Mo?? I don't want to do weld in bungs, because they would be the weak part of the arm, and the weld would not be as strong as the material around it, and I'd have to pay to have it heat-treated and i'm a poor bastard...
I thought those threaded inserts were a close slip fit? If so the weld really isn't going to see a lot of load.
 

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elf_cruiser said:
cool! thanx for the info!!

So - would i have to heat treat it after welding if i used higher grade wire???
If you weld 4130 to 4130 or 4340 using ER502 wire you don't have to heat treat. If you use 4130 wire, you have to heat treat, but it is simple. Get ahold of some insulation, use a rosebud to heat the tube just past the point of glowing, wrap it with insulation, and let it cool itself off slowly.

If you use 70S-X wire you are correct, the weld will be weak.
 

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Chromolly is tougher to tap than mild steel, but you can use a regular bottoming tap if you must (they don't cut nearly as easily as a spiral point tap). The problem that you might run into is the fact that they take so much force to turn it could break off in the tubing. To reduce that risk you need to use a good tapping fluid. I like tap magic- you can get it from a Big R store if you have one there.

[
 

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So you don't have to buy a spool of wire for your mig un less you want to.. I'm sure you know someone or maybe you have one. Tig weld it with ER80S D-2, this is what code calls for in the chemical plant world. There was a few benefits to working in that crap hole. All the procedures you needed were accusable. No need the heat treat what you are doing. You can buy it by the pound or if you know someone at a welding supply shop they might give you a few.

Anyway for the main question your asking, no you don't need a special tap, lube it and your good to go. Hand tapping chromo is kinda tricky. All though if you don't have the tap already don't buy the cheapest one out there as good stuff isn't cheap and cheap stuff isn't good, for a rule of thumb in tooling.
 

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foley said:


If you weld 4130 to 4130 or 4340 using ER502 wire you don't have to heat treat. If you use 4130 wire, you have to heat treat, but it is simple. Get ahold of some insulation, use a rosebud to heat the tube just past the point of glowing, wrap it with insulation, and let it cool itself off slowly.

If you use 70S-X wire you are correct, the weld will be weak.
Thats not heat treating, that is a poor attempt at stress relieving. The only way to correctly stress relieve is to put the part in an oven as a heat treater would do. But you are correct about the welding wire. Any time you weld 4130 you lose strength in the base material, using the higher strength welding wire is an attempt to fix it and works well when stress relieved properly, but you are best off stress relieving in an oven. You generally use 4130 welding wire when you are actually going to heat treat the part, that's when you quench and temper the part to a higher hardness and strength level.
 

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Discussion Starter · #14 ·
OK, since this thread got resurrected...

I have already got my tubing, 2 pieces of .120 wall. One is 1.01" ID, the other is 1.26" ID. I am gonna use threaded inserts because I couldn't get the right size tubing for a good price that would allow me to tap for 3/4" heims. I looked into a professional heat-treat job, and it would be too much $$ right now, but i could always pull them back off and do it later... I am thinking now that I will cut the tubing, and tack the inserts in, then take the arms to Campbell Ent. and have them TIG welded. Any thoughts or suggestions? What kind of rod should I ask Shannon to use?

Also, I was plannin on making the outer sleeve about 1/4" shorter than the inner tube, leaving about 1/8" on either end for more weld fill area, make sense? Will this be necessary for TIG welding, a good idea or bad idea?? Will it even matter??

Thanks for all the advice guys, keep it coming!
 

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From my experience with TIG, don't tack it for him, just do the prep work as far as drilling holes to plug weld, sand the material clean etc, so all that he needs to do is hold the stuff together, wipe it down with acetone, and blast away. If it goes together easily, then he can do it on the spot easier than dealing with a tack weld of odd material. If it doesn't go together well, then you can press fit it before he even touches it.
 

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Re: Re: tapping 4130 tube?

Azrckcrawler said:


I thought those threaded inserts were a close slip fit? If so the weld really isn't going to see a lot of load.
all the ones I have seen are a fairly tight fit, the weld just holds them in. I don't see why the huge deal is being made, i have never heard of a welded insert "failing" in any manner.
 

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Discussion Starter · #18 ·
well, maybe i should just go ahead and MIG them in myself. Then, instead of paying for TIG welding, go ahead and get them heat treated. The heat-treat would cost about $100, does that sound fair? But it would make the entire link stronger, not just the welds, right?
 

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elf_cruiser said:
well, maybe i should just go ahead and MIG them in myself. Then, instead of paying for TIG welding, go ahead and get them heat treated. The heat-treat would cost about $100, does that sound fair? But it would make the entire link stronger, not just the welds, right?
If you are going to heat treat the arms use the 4130 filler rod or OXWELD 32 CMS, heat treat them to RC 26-30 and have them do a stress relief normalize before heat treating them. I wouldn't use ER80S rod because it is not heat treatable. You might have a hard time finding heat treatable mig rod.
 
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