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German type xxiii 1/72 or 1/32

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  • #61
    I woke up yesterday intending to box up the 1.25 SD work and set it aside as I don’t have much time to prepare some subs for the JCC get-together this Sunday – our clubs first model boat outing of the year.

    But, as you can see, I continued work on this aggravating yet seductive, 1.25” diameter, static-diving type SubDriver project. It’s been a total *****, but I love the challenge -- that love expressed as screams of rage and sound of tools bouncing off the shop walls.

    Last night I poured the second half of the rubber tool needed for the new parts previously discussed.

    Here I’m embedding the masters in clay in preparation of making a pour to create the first half of the two-piece tool.



    Pouring the second half of the tool last night. This work done just in time to catch an episode of Bob’s Burgers. Thank God! Then, off to bed. By morning time the rubber had cured and the tool opened up, the masters removed and put in safe storage, the vent and sprue channels cut out, and I was ready to cast the new parts for the little SD’s.



    I cast my resin parts from the excellent Alumilite polyurethane resins, either the ‘fast’ or the ‘slow’ kind. Simple tools that fill quickly, like this one, permitted me to use the ‘fast’ cure resin. By afternoon time I had three sets of parts in hand.

    In background you can see two sets of parts up against the wall as I pour the just catalyzed resin into the tool for the third set.



    I pressurize the mix while it transitions from the liquid to solid state. This forces any bubbles in the mix to go back into the solution. The pressure (one atmosphere is enough) also forces any bubbles in tool voids to be crushed into the mix. The result is (most of the time) void free cast resin parts.

    The pressure pot here is nothing more than a heavy-duty spray pressure pot pressed into resin work.



    And the result: a set of parts pulled from the rubber tool. Note the arrangement of sprue and vent channels. The sprue and associated runners feed the resin into the cavities of the tool. The smaller vent channels in the tool permit the displaced air within the cavities to escape.

    If you look closely at the center hole of the forward ballast bulkhead you can just make out the encapsulated rubber o-ring used to make a tight friction fit between it and the conduit.



    Two 1.25 SD’s with the new resin parts laid out for integration with the Lexan cylinder pieces.

    In keeping with my practice of making as many system parts easily removable the o-ring fit of the forward ballast bulkhead to the conduit is a friction fit which can easily be parted if the forward Lexan cylinder length has to be pulled from the servo box.



    Not apparent here, but during the casting operation I incorporated a rubber o-ring where the conduit runs through the center of the forward ballast bulkhead. Once the length of the ballast tank has been determined, the conduit is cut to the appropriate length. The conduit, a length of brass tube will be provided the customer over-size. The after end of the conduit will eventually be CA’ed to the forward end of the servo box.



    Vent valve open. The ballast sub-system servo is in the ‘vent’ position. In that condition the LPB motor does not run and the ballast tank floods through the open bottom flood-drain hole. As air vents out of the tank it is displaced by water, diving the boat.

    The flat channel upon which the rubber element slides is cut with an end-mill of a diameter slightly larger than the disc shaped rubber element.

    And note the magnet atop the rubber element, and the magnet below within the ballast tank. These magnets work to press the rubber down tight against the channel insuring a gas tight seal. The magnet within the ballast tank is of a diameter slightly bigger than the vent hole, this prevents it from working its way out during valve operation. As the rubber element and its magnet slides atop, the lower magnet slides along with it within keeping a compressive force between rubber element and Lexan cylinder.



    Vent valve closed. The ballast sub-system servo is at its ‘neutral’ position – vent valve closed, LPB off. When the servo goes to the ‘blow’ position the vent valve remains closed as you see here and the servo shuttle pushes the limit-switch to close the circuit to the LPB’s motor. The LPB takes a suction from atop the sail (presumably broached, but the pump can handle water without damage), compresses the air and discharges it into the ballast tank, blowing out the water through the open flood-drain hole in the bottom of the ballast tank.



    And here’s a look at a similar small SD slide-valve -- this one better illustrating how the ballast sub-system servo, through the magnet shuttle sitting atop the servo box, is linked to the rubber element of the vent valve mechanism.

    The Z-bend in the pushrod permits fine adjustment of the rubber elements position over the vent hole.





    David


    "... well, that takes care of Jorgenson's theory!"

    Comment


    • #62
      David,
      What is the diameter of the magnet on the inside? I am asking for a reason.
      If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

      Comment


      • #63
        Originally posted by trout View Post
        David,
        What is the diameter of the magnet on the inside? I am asking for a reason.
        This one, Tom:

        http://www.gaussboys.com/store/index...scs/d0301.html

        David
        "... well, that takes care of Jorgenson's theory!"

        Comment


        • #64




















          David
          "... well, that takes care of Jorgenson's theory!"

          Comment


          • #65
            This looks great! Now im getting excited to get going on one myself. Thanks for sharing Dave. And once again just let me know when you have that second unit done so i can ask Bob to invoice me.

            This is is amazing
            ... a computer once beat me at chess, but it was no match for me with kickboxing!!

            Comment


            • #66
              Originally posted by matthewnimmo View Post
              This looks great! Now im getting excited to get going on one myself. Thanks for sharing Dave. And once again just let me know when you have that second unit done so i can ask Bob to invoice me.

              This is is amazing
              Yeah. It's been a long, tough slog, but I think we're almost there, pal. I should have a new post every other day from this point to assembling your unit. Almost there.

              David
              "... well, that takes care of Jorgenson's theory!"

              Comment


              • #67
















                David
                "... well, that takes care of Jorgenson's theory!"

                Comment


                • #68


















                  David
                  "... well, that takes care of Jorgenson's theory!"

                  Comment


                  • #69
                    I have two questions. If you do this, "elimination of the Lipo-Guard/Battery Link Monitor has simplified wiring and frees even more space within the cylinder." then what protects the battery? and, the second question, how do you accurately drill the centre holes on the new props that you have cast?

                    Comment


                    • #70
                      Originally posted by HardRock View Post
                      I have two questions. If you do this, "elimination of the Lipo-Guard/Battery Link Monitor has simplified wiring and frees even more space within the cylinder." then what protects the battery? and, the second question, how do you accurately drill the centre holes on the new props that you have cast?
                      Without the circuit that protects the battery it become incumbent on the driver to watch his run-time and use of the throttle. Most operations have such a long run time with these high capacity batteries that you become bored with it before the battery is half consumed. But, as a rule, if you can fit the device -- be it BLM or Lipo-Guard -- install it!

                      As to the bore in the cast metal propeller hub, that's done by inserting a stainless steel mandrel into the lower half of the two-piece rubber tool that gives form to the cast propeller. Like So:













                      David
                      Last edited by He Who Shall Not Be Named; 05-11-2018, 09:35 PM.
                      "... well, that takes care of Jorgenson's theory!"

                      Comment


                      • #71
                        Genius. Thanks.

                        Comment


                        • #72
                          You guys that like those tiny tub toys are crazy! The engineering needed to get it all working is damned admirable, but why you'd choose to subject yourself to that stress is beyond me.

                          If they turn your crank, good on you, but I'm sticking with the boats I don't need tweezers to work on!

                          Comment


                          • #73
                            Originally posted by SubHuman View Post
                            You guys that like those tiny tub toys are crazy! The engineering needed to get it all working is damned admirable, but why you'd choose to subject yourself to that stress is beyond me.

                            If they turn your crank, good on you, but I'm sticking with the boats I don't need tweezers to work on!
                            Guilty as charged, sir! But, when it comes to tiny, Tom has me beat by a mile. And Manfred is also a nut-ball for the small stuff he runs in a credible manner.

                            David
                            "... well, that takes care of Jorgenson's theory!"

                            Comment


                            • #74
                              Reading this thread with both admiration and incredulity!

                              It's a touch of masochism perhaps on behalf of the builder, I just can't see beyond certain scales, partly why I don't do model railways any more, anything under 1/50 and my eyestrain kicks in. My next kit after my U-Boat is in 1/20!

                              Fun to watch all the same.

                              Rob
                              ''We're after men, and I wish to God I was with them........!''

                              Comment

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