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  • Back to Steam--

    I have always been intrigued by the Stephensons Link reversing mechanism that was used on some steam engines. While searching for information about it, I was directed to "GrabCad", a site where 3D models can be downloaded free of charge. There is a complete and very detailed model of a small two cylinder steam engine, 3/4" bore x 3/4" stroke, with the reversing mechanism on it. It is quite a lovely model, and it is obvious that many of the major components are castings. This afternoon I have been playing on my CAD system to see what would be involved in making this engine from bar stock. This is what the engine looks like as downloaded.
    Brian Rupnow

  • #2
    The most complex casting is that of the cross-head and the two supporting legs which hold it in position. If I was a real fanatic about it, I might be able to carve this from one lump of metal, but it would be a very trying exercise---and there are two of them.
    Last edited by brian Rupnow; 09-04-2017, 04:17 PM.
    Brian Rupnow

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    • #3
      It appears to me that this could be fabricated from three pieces of either steel or brass, silver soldered together. It wouldn't be nearly as pretty as the casting, but should function the same, and be much, much easier to fabricate. The round portion is pretty straightforward lathe work, and the legs could be fabricated from either one or two separate pieces. It might be tricky to turn the radius in the leg where it has to match the outside diameter of the round cross head, but that is simply a matter of fixturing.

      Brian Rupnow

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      • #4
        Like I said--Not nearly as pretty, but much closer to the scope of what I feel I can fabricate from bar stock.
        Brian Rupnow

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        • #5
          Originally posted by brian Rupnow View Post
          The most complex casting is that of the cross-head and the two supporting legs which hold it in position. If I was a real fanatic about it, I might be able to carve this from one lump of metal, but it would be a very trying exercise---and there are two of them.
          That doesn't look like an insurmountable weldment...got the component part lines, fillets & all.
          Len

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          • #6
            Well, maybe not insurmountable if you are an experienced tig welder with your own tig set-up. Keep in mind though, that the small outside diameter of the round part is only 13/16" in diameter.
            Brian Rupnow

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            • #7
              Brian, how about milling some holes or slots in the RHS legs?

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              • #8
                3D print the GrabCAD parts with a suitable filament and get then cast as 'lost filament' bronze or iron castings. Some PLA filament is suitable

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                • #9
                  Stephenson valve gear gave way to Walshaerts(sp)? which later started to give way to... I forget... Anyhow, if you want to experiment with different valve gear, look up Charlie Dockstadter's programs. He has a ton of them, both inside and outside expansion. I.E. Piston valve vs traditional.

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                  • #10
                    That's a Stewart model. 10 double v I think.
                    My first casting based steam was the Stewart single 10V.
                    Some of pu U.K. Folks should recognize it

                    Very good castings at the time.
                    Should be relatively straightforward to duplicate

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                    • #11
                      It is the Stuart Double 10, basically two 10Vs on a common base casting.
                      I thought everyone knew these basic Stuart models, they have been so all pervasive for half a century.

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                      • #12
                        Originally posted by awemawson View Post
                        3D print the GrabCAD parts with a suitable filament and get then cast as 'lost filament' bronze or iron castings. Some PLA filament is suitable
                        ---If I cared to spend the money, I'm sure I could have it 3D printed. However, I would rather fabricate the parts. For me, the important aspect of making something like this is more about making a functional part with the machinery I have in my little shop.--Brian
                        Brian Rupnow

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                        • #13
                          Originally posted by brian Rupnow View Post
                          ---If I cared to spend the money, I'm sure I could have it 3D printed. However, I would rather fabricate the parts. For me, the important aspect of making something like this is more about making a functional part with the machinery I have in my little shop.--Brian
                          Hell, I'll 3d print it for you out of PLA for free, just pay postage

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                          • #14
                            I have a similar problem. I have been working on William Harris steam donkey off and on for quite some time. I machined the steam cylinders out of Durabar round bar stock by boring them undersize then setting them up on the rotary table to mill the outside. That's all done now and the end covers, pistons and rods are all made and the bores are finised. I just finished lining everything up and drilling the mounting holes. That is all looking pretty good thanks to my new DRO on the new mill. It made the job of getting the holes exactly where they should be a lot easier. Now I have to figure out how I am going to cut the steam ports in the cylinders. The problem is they don't go straight through. I have two ideas. First was to mill slots in the cast iron and then make a cover plate out of some nice thin brass material I have to cover the parts of the slots that don't need to be exposed and go between the cylinder and the steam chest. I am not sure how I can make a good tight seal between the cast iron cylinder and the brass. The other method I had in mind was to try and drill or mill the holes through the cast iron cylinders then plug the ends that should not be open with something like JB weld or Marine Tex. I am making the rest of the parts first so I know exactly where the holes or slots need to be. I might have to take some scrap pieces and do some experimenting before tackling the real thing. As anyone who has tried to build one these knows. The drawings in the book leave a bit to be desired as far as accurate dimensions go. This one will be interesting to follow Brian to see how you make out.
                            Larry - west coast of Canada

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                            • #15
                              This is going to get interesting. Although the solid models have been designed in inches, it appears that in some places the numbers used may be direct conversion from metric. Also, the bolts used are 7BA and 8BA, which I am not familiar with. I will be converting the fasteners to Imperial sizes, mostly #5-40 and #4-40.
                              Brian Rupnow

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