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ZB-1, ZB-2: Scratch Build Cylinder design for limited Production by Zero Bubble.

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  • #46
    Hello David,

    Thanks for getting back so quick. I have pretty much created parts very similar to yours and as you have seen, put them through testing for fit and water tight integrity. They have passed. I will be using this design. However I could really do with you input about my previous post about orientation of parts from molding. The emphasis being on how to mold these parts as accurately as possible, which I am confident I should be able to do.

    thanks,

    David H

    Comment


    • #47
      Originally posted by Davidh View Post
      Hello David,

      Thanks for getting back so quick. I have pretty much created parts very similar to yours and as you have seen, put them through testing for fit and water tight integrity. They have passed. I will be using this design. However I could really do with you input about my previous post about orientation of parts from molding. The emphasis being on how to mold these parts as accurately as possible, which I am confident I should be able to do.

      thanks,

      David H
      The best practice with cast parts with a bore to them is to orient the tools (molds) flange faces -- the parting plane -- parallel to the axis of the parts bore. Like the tool on the left, not the tool on the right. Examples of best practices pictures below, my friend.











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

      Comment


      • #48
        Thankyou David.

        Gold as usual.

        David H

        Comment


        • #49
          Hello David,

          just one thing,

          could you post some photos showing this detail in a little more depth?

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          This is what I am really interested in. I will soon be posting the write up on the push rod glands. I have already molded and made some just like yours.
          These pics here show parts that are very similar to the ones I want to mold.

          Once again,

          Thank you for the info and advice...

          David H

          Comment


          • #50
            Originally posted by Davidh View Post
            Hello David,

            just one thing,

            could you post some photos showing this detail in a little more depth?

            Click image for larger version

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            and


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            This is what I am really interested in. I will soon be posting the write up on the push rod glands. I have already molded and made some just like yours.
            These pics here show parts that are very similar to the ones I want to mold.

            Once again,

            Thank you for the info and advice...

            David H
            BEHOLD!!!!















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

            Comment


            • #51
              Thank you David,

              What I was getting at was to have a closer look at the silicon mold that created those outer supports. However thank you for the added pics.

              Time to create the molds for the push rod glands.
              For many years I have been using a push rod gland simply made up of a small off take barb combined with a small piece of nitro tube and an O-ring. For some time I have been looking at Daves, push rod seal design and though that it was beautifully simple. I thought that I could produce something like that. I had tossed up the idea of producing a design similar to what I had been using however thought I would give the embedded O ring gland a try.

              Weeks ago I machined up a series of brass pieces that would serve as the outer housing for the gland. I machines a flange on the out side to differentiate a bit from David's and as a stopped for the outer end. I then took a piece of 2.39mm brass rod and ordered some small o rings from a Beaut little supplier in the US called "O-rings and more". Swift delivery. I could have used a smaller diameter push rod, but this in the one I have been using for years.It is a good dia.

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              Eventually I reduced the flange width on each of these. As you can see the O ring looks pretty bit compared to the diameter of the brass gland. This caused concern, however I pushed ahead anyway confident that the pour of urethane would close any gaps.

              I took a block of MDF and once again started creating the structure for creating the silicon molds. This involves taking the parts and arranging the layout for them. In this mold I also would produce the two parts for the electrical cable conduit through the end cap. The development of this could be another write up.. one day... I have pretty much taken Davids advice, that you should really angle your pieces to the horizontal so that all the bubbles will rise to the top.

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              The Acetl white pieces are the electrical pass through's for the wires in and out of the Cylinder. KISS. These brass tubes are hollow and allow the wires to be passed through, glued in and silicon'd.

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              The balsa strips are the runners that run to the top of the mold. The wire strips are the air vents. Around the runners I will press down Play-doh to make funnels and seal around the flat planes of the parts in their place.

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              Above: The first half of the mold has cured. I have unscrewed the side off that butts up against the play-doh funnels. I will then pull the rubber mold off the base. You have to make sure that the silicon has clearly cured. If the outer layer of silicon has set but it is still liquid immediately underneath and it tears as you pull. That's not great.

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              Once this has come off I can start turning around the mold for the second half.

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              The darker lines are where the paper clip wire for the air vents have been removed. I have filled them with extra lanolin so that the silicon from the top mold does not fill them.
              I am careful to remove all the lanolin off around the register bumps.

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              Here is the finished mold. The inserts of brass come out. All they do is create the hole and hold the O ring in place to be embedded.



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              Close up and pour the mold. I will go into this next time..


              David H









              Attached Files

              Comment


              • #52
                I am always saddened when I hear that one of the 24 have left us..

                I only just heard, because it didn’t even make the news once again, Alfred M Worden, Command module pilot of Apollo 15 has left us.
                The first CMP of a Lunar ‘J mission’ and the record holder of being the most isolated human in History has gone.

                This photo shows Worden in the middle with David Scott on left and Jim Irwin LMP on the right.

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                We only have Commander Dave Scott left from 15.

                These guys have always been heroes of mine. The United States should be proud of them. I was only 1 month old when the last mission landed. I wish I could have seen them

                Regards,

                David H
                Last edited by Davidh; 03-24-2020, 10:43 AM.

                Comment


                • #53
                  Hello all,

                  Bunkering down for this Covid-19 business. Doing all my classes from next week on-wards via Zoom. But this does give me less commute time which could potentially mean more workshop time, Yay!

                  So I placed the brass insert rods into the mold and then some brass tube into the Electrical connectors that I have made. Slip O rings over the solid brass inserts to embed into the Polyurethane. Then close up the mold and then strap two pieces of plywood to either side and rubber bands, then mix up and pour some urethane. Place the mold into the pressure pot and sit at 2 ATM for about 1 hour just to get really stiff and fully cured.

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                  After that, de-mold the parts. These have just come out of the mold and need a little sanding. You can clearly see the rough part line running down the axis of the top gland part and down the electrical connection off to the right. I then pulled out the brass rods from the Glands and checked for friction. The 'O' rings being very well embedded. There is a little friction they should certainly seal. Getting some fine 800 grit and giving the rod a fine smooth sanding just to reduce the friction. Mind you the servo's that I use should have plenty of torque and overcome the stiffness that is there.

                  So i cleaned up two of the glands and pressed them into the two top holes of the stern end cap on the test piece that I have spent a fortnight testing with the shaft housings. I used some silicon to glue and seal around the gland as it was pressed into the end cap. Tight fit. As long as these cast parts don't leak and don't create too much friction then i will not have wasted too much silicon!

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                  This pic shows the push rod gland in place and not leaking. It was a little hard to push and pull on the brass shaft. So I decided to bend up these small lengths so that I could push and pull underwater to check for sealing.

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                  So far so good...

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                  I then took the electrical connectors and ran two wires through. I then ran some silicon around the outside of the plug and placed it through the hole in the front test end cap. Had to mark out and drill that first. Then pushed some more silicon into the brass tubes and some heat shrink.

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                  Heat shrink over silicon, over wires...

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                  The plug in the middle of the Renshape test piece is where the original hole was for securing to the lathe. I then filled this in with a small piece of Renshape. Then I will fill over and sand.

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                  This allows me to run cables from the inside out to a battery to really run the motors underwater easily. Looking really good, no leaks...

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                  These are the first cast pieces for the design. They don't leak. I am very happy with this. All i need to do now is just check that the brass rods that pass through the gland don't create too much friction when I put these into limited production. The embedded 'O' ring Idea is brilliant. Next will be the creation of the molds for the stern motor shaft supports and housing. Then once again the testing of the first production pieces just like here.


                  Keep isolated and keep safe everyone...

                  Reduce your cabin fever by talking to me....

                  David H



                  Comment


                  • #54
                    Here's my trick to open up the bore of the pushrod seal body so you reduce the friction between it and the pushrod: Ream out the bore with a drill bit that is about .002" larger in diameter than the pushrod you are using. First coat the bitt with bee's wax then open up the seal body bore with it. The wax will let the cutting edges of the bits flukes push the rubber seal out of the way rather than cutting the O-ring, but the bit will still cut into the resin portions of the seal body's bore. Further: lubricate your pushrod with silicon grease, AKA 'distributor grease' available at car supply stores. These two steps will greatly reduce the friction between seal and pushrod.

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

                    Comment


                    • #55
                      Hi David,

                      Nice, will do. Got that shaft extension write-up? I’ll understand if you’ve been too busy.

                      Dave.

                      Comment

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