Mobius Skipjack in Napa Ca

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  • Greevesman
    Ensign
    • Dec 2016
    • 48

    Mobius Skipjack in Napa Ca

    I an old retired guy in Northern California that somehow got interested in RC submarines. No background in subs as I was in the artillery. In any case I found David Merriam who sent me the links to his articles and suggested the 1/72 Mobius Skipjack. I ordered the hull kit, fittings kit, and a sub-driver. The hull kit and fittings have arrived and the sub-driver will arrive after Christmas. I have an engineering background and a fairly complete machine shop, small mill, lathe etc. I am 'handy". The hull sections are out of round, 90 degrees to each other. The forward sections are about three tenths of an inch wider than taller when put together, The aft sections are about four tenths of an inch taller than wider, in addition, the aft sections have a small vertical bow fore and aft which disappears when you compress the sections with your hands so they are round.
    SO, I think I need to heat them so they fit better if I am to be able to make the hull joint work as shown in Davids manual.
    I am not comfortable trying to heat and bend by hand so I think I need a jig.
    David suggested the temperature to bend the plastic is about 230 degrees. I have an infra red thermometer and I can test using scrap plastic fins and rudder pieces. He also suggested spreading or compressing 20% more than the desired finished dimension.

    Here's what I was thinking.

    Looking at the hull halves

    Front section needs to be compressed horizontally, Upper with pins, lower with holes., rear section needs to be spread horizontally.

    I know how much for each at the hull opening.

    Take a flat piece of plywood.

    For the upper forward drill holes for the pins closest to the joint the proper amount to spread +20%

    Mid set of pins prorate the amount to spread passed on distance forward

    Front pin no change of course.

    Put the forward upper hull half pins in the holes.

    Heat to spec temp and let cool.

    Put dowels in the holes on the board.

    Put lower forward hull half on the dowels.

    Heat to spec temp and let cool.

    For the after halves drill appropriate hole pattern spreading the halves and do same routine.

    Does anyone have experience making adjustments such as these? Thanks in advance.
    I will probably build the Scamp as it was constructed at Mare Island and I am only 13 miles north.
  • He Who Shall Not Be Named
    Moderator
    • Aug 2008
    • 12255

    #2
    I gave Bruce the wrong dope as to the temperature needed to permanently re-form the polystyrene plastic hull. It should be 212, not the 230-degrees I initially told Bruce. 212-degrees is the glass transition temperature -- the temperature at which the plastic becomes pliable, but does not melt. Any higher and the stuff melts, ruining the work.

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    • Greevesman
      Ensign
      • Dec 2016
      • 48

      #3
      Thank you for saving me! I plan on doing some tests of the scrap plastic rudders/planes. Maybe in the oven. Increasing 10 degrees at a time maybe.

      Comment

      • greenman407
        Admiral
        • Feb 2009
        • 7530

        #4
        Originally posted by Greevesman
        I an old retired guy in Northern California that somehow got interested in RC submarines. No background in subs as I was in the artillery. In any case I found David Merriam who sent me the links to his articles and suggested the 1/72 Mobius Skipjack. I ordered the hull kit, fittings kit, and a sub-driver. The hull kit and fittings have arrived and the sub-driver will arrive after Christmas. I have an engineering background and a fairly complete machine shop, small mill, lathe etc. I am 'handy". The hull sections are out of round, 90 degrees to each other. The forward sections are about three tenths of an inch wider than taller when put together, The aft sections are about four tenths of an inch taller than wider, in addition, the aft sections have a small vertical bow fore and aft which disappears when you compress the sections with your hands so they are round.
        SO, I think I need to heat them so they fit better if I am to be able to make the hull joint work as shown in Davids manual.
        I am not comfortable trying to heat and bend by hand so I think I need a jig.
        David suggested the temperature to bend the plastic is about 230 degrees. I have an infra red thermometer and I can test using scrap plastic fins and rudder pieces. He also suggested spreading or compressing 20% more than the desired finished dimension.

        Here's what I was thinking.

        Looking at the hull halves

        Front section needs to be compressed horizontally, Upper with pins, lower with holes., rear section needs to be spread horizontally.

        I know how much for each at the hull opening.

        Take a flat piece of plywood.

        For the upper forward drill holes for the pins closest to the joint the proper amount to spread +20%

        Mid set of pins prorate the amount to spread passed on distance forward

        Front pin no change of course.

        Put the forward upper hull half pins in the holes.

        Heat to spec temp and let cool.

        Put dowels in the holes on the board.

        Put lower forward hull half on the dowels.

        Heat to spec temp and let cool.

        For the after halves drill appropriate hole pattern spreading the halves and do same routine.

        Does anyone have experience making adjustments such as these? Thanks in advance.
        I will probably build the Scamp as it was constructed at Mare Island and I am only 13 miles north.
        Sounds like you got one that was REALLY out of wack. Mine was very mild, so I didnt need to do anything to it. Have you considered sending it back to exchange? Oh thats right..................nothing on the shelves to exchange with. Oh well. Be VERY careful.
        IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

        Comment

        • Albion
          Captain
          • Dec 2008
          • 651

          #5
          Great Kit, but i'm also spending an inordinate amount of time trying to get the hull closure right.. worth it though!
          Next time someone points out it takes 42 muscles to frown, point out it will only take 4 muscles to b1tch slap them if they tell you how mnay muscles you need to smile:pop

          Comment

          • Greevesman
            Ensign
            • Dec 2016
            • 48

            #6
            Are you having success?
            Does yours resemble what I described? Front, too wide, Aft, too tall?
            How are you correcting?
            Thanks

            Comment

            • trout
              Admiral
              • Jul 2011
              • 3545

              #7
              In David's kilt are some ribs or bulkheads that form the mounting bracket for the Sub-Driver, will that not help make adjustments? There is also a front assembly for torpedo tubes, that too might help get things in shape.
              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

              • trout
                Admiral
                • Jul 2011
                • 3545

                #8
                Oh, I forgot my manners, welcome aboard! You have picked an incredible kit for a first sub. It is a perfect beginners sub as well as one that will make a seasoned rc submariner squeal. This sub is a bullet underwater or a nice slow moving sub if you want. It looks the part and will perform well. Glad you are here!
                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

                • Albion
                  Captain
                  • Dec 2008
                  • 651

                  #9
                  Originally posted by Greevesman
                  Are you having success?
                  Does yours resemble what I described? Front, too wide, Aft, too tall?
                  How are you correcting?
                  Thanks
                  Bulkheads have solved the last two areas, one near the stern in top half. Lower half has bulk head which supports props haft bearing. One at front of lower hull where the z cut is. Top half is better shape because it has both lower and upper parts at that point. I also have some magnets and alignment tabs. Bit belt braces, but overall it's quite solid and easy release mechanism between halves.
                  Next time someone points out it takes 42 muscles to frown, point out it will only take 4 muscles to b1tch slap them if they tell you how mnay muscles you need to smile:pop

                  Comment

                  • Greevesman
                    Ensign
                    • Dec 2016
                    • 48

                    #10
                    Could you post pictures? So you fabricated bulkheads. Near the stern in the top half. Is it aft of the cut or in the removable top half? Sounds like aft. What are "Belt Braces"
                    Thanks for the info. I probably won't get much done until after new years as one of the daughters is getting married again. But I like to plan things out.

                    Comment

                    • Greevesman
                      Ensign
                      • Dec 2016
                      • 48

                      #11
                      Well, I have started to drill holes on the upper hull. On the lower hull there are MBT flood / drain gratings that need cut out. Davids directions show each one hogged out to maximum x y dimensions. Each one is made up of three gratings with two separator bars running fore and aft. Has anyone taken the trouble to carefully open each one in the three narrow fore and aft slots? I think it could be done. If I were to do that would it allow enough flow?
                      Thanks

                      Comment

                      • greenman407
                        Admiral
                        • Feb 2009
                        • 7530

                        #12
                        If you did it, it would look nice but it wont make any difference to water flowing in and out. There are plenty of other holes. If you do it , be careful as it would be easy to muck it up.
                        IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

                        Comment

                        • trout
                          Admiral
                          • Jul 2011
                          • 3545

                          #13
                          I have seen others put in etched brass in there, but when putting the sub in or out of water, you will need good flow. Careful on some of the holes there were some mistakes that I documented on my build.
                          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

                          • Greevesman
                            Ensign
                            • Dec 2016
                            • 48

                            #14
                            Still poking holes in the hull. In part 6 of David's excellent manual it describes cutting "A square hole who's forward transverse line is 3/16" from datum, and after transverse line is 5/8" from datum. I laid it out as specified. When I project a bright light from inside the hull it appears that the after transverse line of the hole is in front of the internal reinforcing rib. On the next page there is a photo that shows adding the 1/4" x 1" addition for the pushrod connection. In that photo, it appears that the internal reinforcing rib is cut by the main rectangular hole. As mine is laid out, the rib will not be cut by the main rectangular hole. It will be cut by the 1/4" x 1" extension for the pushrod. I have checked it twice. Therefore my rib must be in a different location than the photo by about 3/16". These internal ribs are used as a basis for laying out several amputations, and for mounting things.

                            Comment

                            • trout
                              Admiral
                              • Jul 2011
                              • 3545

                              #15
                              Please look at my build. I ran into errors on his instructions and posted corrections. If you can not find the build, I can post a link.
                              Peace,
                              tom
                              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

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