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Intro and metal question

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  • Intro and metal question

    Hello to everyone. I am new to this site as far as posting goes, but I've been monitoring it for about two or three years now. I've been a woodworker all my life, but about five or six years ago I decided to buy a lathe and try my hand at metalworking. I've gotten involved with it quite a bit as a hobby and enjoy it very much. I also own a Taig mini mill. Over the past few years I've also collected many of the items that go along with this hobby. I purchased a Grizzly surface planer many years ago which was made in Taiwan. I was very happy with the quality of it for the money, thus I bought a Grizzly 9 x 20 lathe five or so years ago and was very disappointed when I saw that made in China label on it, but for the money it was a good machine to learn on. I've since followed the advice of this for on and completely overhauled the machine replacing all of it with stainless hardware and such upgrades that were recommended on this form. I progressed to the point and have the machine to the point that I can now machine easily to within a thousands or more. I do have a background in metals and engineering. Enough about me. My first question. I have a part I want to make that the specs call to be made out of 4130 chrome Molly. It is then required to be heat treated to 125,000 psi and cadmium plated. Why could I not use stainless steel 17-4 instead. In its normal state it is more than 125,000 psi and would require no heat treatment or cadmium plated since its going to be in contact with aluminum. I guess the main question is how well does 17-4 stainless machine? Is it similar to 4130 or 4340 both of which I have machine with no problem. Thanks all.

  • #2
    As long as the material properties meet your requirements, it shouldn't make much of a difference. With all things equal, cost or availability is usually the determining factor of what material to use.

    You didn't mention the tolerances you expect to hold. Watch out for thermal expansion with the stainless. If you rough it out then take your finish immediately after, you'll have a nasty dimensional surprise after it cools down. If you need to tap holes, avoid chrome clad roll form taps, the nickel in the coating & the stainless like to hug one another. In other words tapping will become a "snap"

    I’m sure others will put their 2 cents in, who knows, before the evenings out your liable to end up a dime or two!

    Ed Pacenka


    • #3
      Jim, in the shop that I work in we use 17-4 daily. It generally comes in at condition "A", which I believe is it's softest state. We usually heat treat it to condition H900, which is it's hardest state which is usually around 42-45RC. It cuts very well in this state and it seems to stiffen it up some which helps in the shaft making that we usually use it for. I believe condition H1050 or H1150 is the most machinable state but it cuts well in all of them, a lot better than the 300 series stainless. One thing about 17-4, it is a grade of stainless but it can rust with the right conditions, but it will take a while.
      Jonathan P.


      • #4
        Cost is not a concern since I only need two feet of 3/4" round Rod. I am making four pins that are one half-inch round with a 3/4" shoulder about two thirds the way on them. Each end has a one half-inch stub that will be threaded for a 3/8 bolt. The long portion we'll be bolted stationery while the short end will receive an aluminum arm that rotates slowly. Tolerances will be to within .oo1 inch.


        • #5
          For a good read on stainless, go to they have a ton of info on stainless.



          • #6
            Machines better than 300 series & 400 series as it does not work-harden (that's a blessing!) Easily welded. Ed mentioned possible difficulty while tapping, and this might also show up as a galling problem, depending on fit, loading, phase-of-the-moon, and other variables.

            Barry Milton
            Barry Milton


            • #7
              Thank you gentlemen for the input and thank you Chris for that web site. I found an interesting caveat on the alleghenyludlum web site. Their spec sheet said that it is hardly ever put into service in the annealed condition. Makes it much more susceptible to stress corrosion cracking especially when exposed to chlorides in this condition. But if you can heat treat it first and then turn the part, as you indicated japcas, then that's not so bad. This would eliminate the problems of dimensional stability associated with heat treating after manufacturing a part. This part will be out in the weather but not directly in contact with most moisture. Thanks again all!