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Overcrank Single cylinder engine

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  • Overcrank Single cylinder engine

    I was so taken by the twin cylinder Potty Overcrank Wall Engine designed and built by Sbwhart http://www.homemodelenginemachinist....?topic=12367.0 that I may attempt to design and build a single cylinder Overcrank engine. One or two years ago I built my version of Elmers #33 mill engine, and it turned out quite fine. http://www.homemodelenginemachinist....p?topic=7340.0 (That was the engine that powers my Pumpjack.) It was a double acting single cylinder engine, with a slide valve arrangement similar to the valve arrangement on the Overcrank engine built by sbwhart. I will probably plaegerize the design of both the aformentioned engines and add some unique design elements of my own. Although I doubt that my work will ever approach that of Elmer Verbourg or Stew's, my engines do seem to run reasonably well. I will be simplifying the design, and configuring it to work with my favourite #5-40 fasteners. The Elmers#33 engine had a 1/2" bore and 1" stroke, while the Overcrank engine by sbwhart had a 20mm dia bore and a 36mm stroke. (Roughly 3/4" dia. and 1 1/2" stroke). I don't like to work on very small parts, however I don't want to design an engine so large that the modellers with smaller capacity lathes and mills are unable to build from my plans. The design will be done in Imperial units----(I can work in metric, but I'm much more comfortable with inches.) I will design in Solidworks 3D software, but the published drawings will be saved and posted here in a .pdf format. Welcome aboard, hope you enjoy the ride.----Brian
    Last edited by brian Rupnow; 09-08-2011, 08:06 AM.
    Brian Rupnow

  • #2
    Thank you for the interest. I just checked my inventory of chucking reamers, and see that I have a brand new 5/8" diameter reamer. Since this is "half way" in size between the two engines which I am using as examples, I believe my engine is going to have a 5/8" bore and a 1 1/4" stroke. I like to machine my bores using a reamer, because it gets around the issue of tapered bores very nicely, and I can turn the piston diameter "to suit". This only works when I can machine my cylinder bore as a complete "thru-hole", and since the cylinder will have a bolt on endcap at both ends, this will work out very well.---Brian The following link will take you to the completed twin Overcrank engine by sbwhart.--an amazing piece of work.
    http://www.homemodelenginemachinist....?topic=14847.0
    http://madmodder.net/index.php?topic=4201.msg52284#new
    Brian Rupnow

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    • #3
      Well, there we go---that wasn't so bad!! Basically, I took the 1/2" bore x 1" stroke cylinder from my version of Elmers 33 mill engine, and redesigned it for a 5/8" bore x 1 1/4" stroke. I am going to use the exact same steam chest and valve, so I kept the cylinder the same in the critical area where the steam chest fits up to it. Of course the raw stock for the cylinder jumped up from 1.031" square to 1 1/4" square to accomodate the larger bore. The #33 engine cylinder was 1.375" long with a 1/4" thick piston and a 1" stroke, so I pro-rated sizes to accomodate a 1 1/4" stroke with a 1/4" thick piston, which changed the overall cylinder length to 1 5/8". This is my starting point only. As this design progresses I may have to change/re-arrange things, but now I have a "baseline" to work outward from.
      Brian Rupnow

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      • #4
        Thanks Stew.---After a quick check of available stock, a corporate decision has been reached to use 5/16" diameter stock for the crankshaft with 1/4" x 1/2" bar stock for the crankshaft "webs" or "throws" depending n what you call them. the crank will be built up, pinned, and loctited.
        I am going to post one of Stew's video links here so I can find it for reference as I build.
        http://www.youtube.com/watch?v=FBEsz...ature=youtu.be
        Brian Rupnow

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        • #5
          Dang!!! I got this far this morning, and then an engineering job thats been on hold for 3 weeks was released. That means I have to stop this fun stuff for a while and do some real "money earning" work for a bit. Don't ya just hate it when you have to stop playing so you can earn some dirty old money!!!
          Brian Rupnow

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          • #6
            Job is on temporary hold again. Thats okay---I have sussed out the overcrank guides and the connecting rod. It all works well and everything clears okay. if you click on the top picture you will see an animated video of it working. I just spent 20 minutes talking to my Solidworks provider figuring out how to make an animated video that lasted longer than 10 seconds.


            Brian Rupnow

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            • #7
              GENTLEMEN----We are ready to ROCK!!!! I squeezed out an hour at the end of my day to complete the model and I think it looks great!!! Tomorrow I will root through my pile of aluminum bits and see if I have a peice to start the cylinder. I will create detail drawings and post them as I progress, but my advice is that you don't copy them right yet, because this is a "prototype" and the drawings may change as I get deeper into it. I will post a download for all of the updated drawings at the end of this game, when I have this engine running.----Brian
              Brian Rupnow

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              • #8
                Well, there's nothing like beginning at the beginning!!! Here we have $92 worth of the material that will be used to build this engine.---It won't all be used----Its just that my metal supplier gets a bit oinky if I go in and buy 3" of this and 7" of that---and I don't really blame him. The majority of what you see here is in one foot lengths. The exception to that is the short peice of 5" x 1" x 6" long aluminum flatbar which was found as an "off-cut" and will be used to make my flywheel. And---a couple of peices af brass are shorter than one foot because that stuff costs like gold, and sells by the linear inch.
                Brian Rupnow

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                • #9
                  FINALLY!!! I get to work on my own stuff!!!! Tomorrow morning I will start machining the cylinder. Don't bother to save these preliminary drawings, as they may change before the game is finished. I will post updated and corrected drawings when I know this one runs.---Brian

                  Brian Rupnow

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                  • #10
                    I don't usually make any sort of step by step plan when I machine somethng, as it is not usually needed. However, there are enough steps in machining a cylinder that if you get the sequence wrong you have to end up scrapping it and starting over. Last night I sat at the kitchen table and worked things through in my head and made sketches as I went along. So----this is the sequence in which I will machine the cylinder. I will have to make a drive dog to suit the 1 1/4" sq. bar, but it will be added to my arsenal of strange fixtures.
                    Brian Rupnow

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                    • #11
                      Those of you who are sharp of eye will have noticed that the dimensions on my hand sketch didn't agree with the detail drawing. I noticed that just in time, so no metal was cut, and I have corrected the sketch and reposted it.
                      The first step involved today was to cut a peice of the 1 1/4" square aluminum bar to a rough length (in this case 4"), lay out the centers in the ends of the stock, and put in a countersink in each end in my milling machine.
                      Brian Rupnow

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                      • #12
                        The next step was to build a "drive dog" to transfer torque from the chuck to the part when it is held between centers in the lathe. I meant to take a picture of this drive dog before it was mounted, but forgot. I will post a picture of it later----Basically, it is two peices of angle with the toes welded together and a scrap bolt welded to one corner to engage one of the chuck jaws. Before they were welded together I milled out the radius in the inside corners of the angle so the radius wouldn't interfere with the corners of the aluminum bar. It is drilled and tapped for two 1/4" bolts that are used to "snug it up" to the aluminum part. You will also notice that I am not using a live center in the tailstock.--Why----Because my live center is so short and the lathe saddle is so wide, that I can't engage the tool with the end of the part closest to the tailstock. My "work around" for that is to machine the proper angle onto a peice of 5/8" round bar, give it a liberal dose of lithium grease, and mount it in my tailstock chuck.

                        Brian Rupnow

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                        • #13
                          Here we are at completion of the first lathe operation. No magic here---Used a conventional tool to machine the diameter closest to the tailstock. Then used a cut off tool to plunge cut on the far side of the rectangular "lump" left in the middle. I made about 5 plunge cuts side by side, enough to get my conventional cutting tool into the resulting groove, then machined up to the other square bit still captured in my "drive dog". Then put in a reverse ground tool and took a finish cut from left to right, stopping at the rectangular bit left in the middle. I make use of my home made "carriage stops" for repetitive cuts parallel to the lathe bed, and also the ones I have built and installed for the carriage cross feed.
                          Brian Rupnow

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                          • #14
                            As promised, here is a picture of my "drive dog" by itself.
                            Brian Rupnow

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                            • #15
                              Sticking with THE PLAN---ports and other holes are drilled in milling machine.
                              Brian Rupnow

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