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303 Stainless as crankpins.

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  • 303 Stainless as crankpins.

    I am making a built up crankshaft for a steam engine.. Can folk with experience using 303 stainless running in bronze bearings please comment on any likely problems.I have the material in the right size for the job. Regards David Powell.

  • #2
    303 is soft, and can't be made very hard.
    Southwest Utah

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    • #3
      If it was me, I would use 4140, but maybe that is overkill.

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      • #4
        Bronze will wear out the 303. How long it takes depends on a lot of variables. I don't know the size of the crank pin, but I would tend to go with hardened tool steel. For a already hardened part, maybe a case hardened dowel pin, or some Thompson rod, etc. It would be easy enough to do your own out of drill rod and heat treat it.
        Kansas City area

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        • #5
          Assuming this is a model steam engine? In all reality, how much is one of our engines going to be run and, what kind of work will they be doing?
          I've used 303 stainless for cranks. In fact, I just used it on the crank for my recently posted radial five engine.

          If this is not a model, then I agree, a different material might be considered.

          So, what is it?

          Sid

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          • #6
            A steam engine that runs via steam power and does actual work or a model for display?

            If the later 303 is free machining and will make you happy.

            If you are building a steam engine to run an artisanal beer hops grinding operation then all bets are off.

            Crankpin 303 would be an excellent name for such an arty beer.

            Steam Ground Golden IPA is also an excellent name (-:
            Last edited by Bented; 11-11-2021, 09:05 PM.

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            • #7
              As others say, if it's a model that might run a couple of hours a year, use 303 - it'll last your lifetime.

              Ian
              All of the gear, no idea...

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              • #8
                If it could be made of, say, 1018, then 303 stainless is not so bad either. That's what oil is all about.
                CNC machines only go through the motions

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                • #9
                  Originally posted by chipmaker4130 View Post
                  303 is soft, and can't be made very hard.
                  That was my first thought. SS is not good material for strength.

                  As a model, yes, it might work out very well.

                  Just remember, the smaller the dia of the shaft or crank does not mean it doesnt need just as much strength.

                  303, 304 or even 412 SS is not meant to be a strong alloy. It is very corrosiassian resistant, not all that strong in tensile. JR

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                  • #10
                    Thankyou all for your helpful and interesting replies. There is quite a story here.
                    Toronto Society of Model Engineers was established in about 1933 and has continued successfully ever since.
                    Some folk have remained members for many years, some have been members for only a few years.
                    We have some membership records, but not quite all, for various reasons.
                    A few months ago we were contacted and told that the society had been bequeathed some items.
                    A fellow who, as far as we can tell, who was a member only in 1959 left us his model engines.
                    These were advertised among the members.
                    I was able to purchase, sight unseen a partially built Stuart " Swan" engine ( Twin cylinder high speed marine job 2 inch stroke 21/4" bore, uses 2 sets of Stuart #5 castings along with some specials now no longer made).
                    While It did not really fit in my plans for what I wantedI thought it a worthwhile project.
                    All the work completed , so far , is of excellent quality.
                    The base plate had been started but not completed, I was able to line bore that and got a good parallel bore to fit lubrok bushings.
                    The crank blank supplied is a weldment intended to have bolt on balance weights. I started to machine it, but simply do not like the idea.
                    So I am making my own built up crank from available material. My 5/8" thick crank webs have 5/8 reamed holes which all came in at 0'625.5 within a tenth or so. my 1018 bar is 0.624 but my 303 is oversize at 0.626,( Give or take a tenth or so) and makes a LIGHT force fit in the webs.
                    Since covid came I have been a shop hermit, and have hardly ventured off our garden, so I guess you will all have figured out that I would be tempted to make the crank pins of 303 and the main shaft 1018, all loctited and later taper pinned.
                    For my lifetime the engine is likely only to be an ornament, I simply do not have a big enough boiler to steam it properly.( Rated for 3 bhp at 800 RPM)
                    Regards David Powell.

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                    • #11
                      I don't know what 1018 material is. If I was doing that shaft I'd use silver steel (aka drill rod) in the unhardened state, but then you have to use what you've got.
                      To be honest, I don't like built up shafts. When I was doing my Stuart No.3 compound I cut the shape of the shaft out of steel plate, then, in order to get the 90 degree twist in it, heated the area of the centre journal to bright red, clamped the shaft in the vice and twisted it with a big Stillson wrench. Followed by machining.
                      'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                      • #12
                        1018 is plain .18% carbon steel ....Mild steel
                        Last edited by J Tiers; 11-12-2021, 04:17 PM. Reason: decimal point
                        CNC machines only go through the motions

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                        • #13
                          Originally posted by J Tiers View Post
                          1018 is plain 18% carbon steel Mild steel
                          You mean 0.18% carbon.

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                          • #14
                            Originally posted by J Tiers View Post
                            1018 is plain 18% carbon steel Mild steel
                            Looks like you missed the decimal point... it's .18% carbon

                            Dang, I got scooped.

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                            • #15
                              Bronze is not known to be compatible with chromium, which is present in most stainless steels. That said, most models do not get many hours of running, or high stresses so the wear might not be much of a factor.

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