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Thread: Plasma cutting 4130

  1. #1

    Join Date
    Oct 2011
    Marietta, GA

    Plasma cutting 4130

    I made mention on a different forum about cutting sheet 4130 on my plasma table and people panicked. "Oh that will get you killed!"

    I am not sure why it is going to grow green eyes and strangle me but I gather from the "rapid cool of 4130" comments and all that they believe the process is inherently bad.

    My understanding of the plasma process is hydrogen embrittlement would be a bigger worry. That said you typically finish the part with a file anyways. Remove the bevel and any defects from the manufacturing process.

    To these guys on the other forum, the whole part is compromised once that plasma comes walking into the room.

    What is EAA's TA advice in the topic? I have tried to Google this and don't get back lots of details.

  2. #2

    Join Date
    Aug 2011
    This is interesting to me, and I would like to see what the answers are. Following.

  3. #3

    Join Date
    Jan 2012
    Having never used a plasma cutter, I'm only answering based on what I've read and the lack of other answers. I read many articles on the internet about using TIG to weld 4130, and most of them strongly suggested that post welding heat stress relieving was required to prevent cracking due to the intense localized heat of the process. I've also noted that many, if not most, are using TIG to weld up 4130 tube fuselages over the last 8 years, and those I've questioned about it always reply that they don't heat to stress relieve after welding. None of those aircraft have fallen out of the sky, to the best of my knowledge.
    I don't know what the EAA says about it, but I've never read a comment one way or the other. I would not hesitate to use it if I had one. On the other hand, I gas weld and use a band saw for the most part to cut the steel plate parts.
    Hopefully, someone with real knowledge of the subject will chine in and set me straight!

  4. #4
    Mike Switzer's Avatar
    Join Date
    Jul 2011
    Central Illinois
    This has me curious. I have been using plasma cutters for 30+ years, and in my experience the parts cut are a whole lot cooler than if you do the same cut with a torch. I can't remember if I have ever cut 4130 with one, but I know of a whole lot of dirt track cars that were built from 4130 purchased at Wick's & cut with a plasma & welded up with a Tig. These good old boys are bumping fenders & bumpers every race & the frames don't fail.

    Edit - for the record on my aircraft project I plan on cutting the tube with a band saw & torch welding it.
    Last edited by Mike Switzer; 02-12-2021 at 06:34 PM.

  5. #5

    Join Date
    Dec 2016
    Zionsville, Indiana
    If there is an issue with plasma cutting 4130, it may have to do with the condition of the surface and edges of the metal at the cut. Notice that I prefaced the last sentence with the work "IF". With a gas cut, the heat in the process anneals the are adjacent to the cut. But the very much higher heat of the Plasma might en-brittle the edges which could start a crack. But that could be easily remedied by smoothing the cut edges.

    I have used water jet cutting for brackets but I always smooth the edges and any holes I have cut, I finish them with a ream.

  6. #6

    Join Date
    Oct 2011
    I had a lot of the 4130 parts for my project cut with laser and some were water jet cut. The laser cut parts didn't need any post processing other than I took the edge off with a 3M wheel. I asked an engineer friend of mine if the laser cutting vs water jet would cause any problems with the parts and he said it wouldn't. I did have problems drilling and reaming the holes to size. I had the holes cut slightly smaller. I went through a lot of drills. I think the main problem was my lack of experience.

    The heat applied by gas welding or bending the parts far out weighs the heat from the laser cutting.

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