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Tool time.

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  • #46
    I second that- Thanks David

    these see photos are great.

    David H

    Comment


    • #47
      Hello David and anyone else,

      i I have a new set of questions. As you may be aware I am trying to develop my skills at degassing urethane resins and also RTV silicones. I have a vacuum chamber and have been looking at Vacuum pumps. They are expensive. A friend of mine aware of what I am trying to achieve gave me two small little devices that he said may provide another angle to attack the problem.

      He he gave me a small item called a "vacuum ejector" it simply converts a pressure input into an output vacuum by using a Venturi.

      http://www.smcpneumatics.com/ZH10BS-06-01.html

      we hooked it up to a 2 HP compressor and sure enough to it pulled vacuum, we didn't push it all the was but got up to at least 25 inch of mercury.

      have you used one of these? Do you know if it would do the job?

      thanks,

      David H

      Comment


      • #48
        Originally posted by Davidh View Post
        Hello David and anyone else,

        i I have a new set of questions. As you may be aware I am trying to develop my skills at degassing urethane resins and also RTV silicones. I have a vacuum chamber and have been looking at Vacuum pumps. They are expensive. A friend of mine aware of what I am trying to achieve gave me two small little devices that he said may provide another angle to attack the problem.

        He he gave me a small item called a "vacuum ejector" it simply converts a pressure input into an output vacuum by using a Venturi.

        http://www.smcpneumatics.com/ZH10BS-06-01.html

        we hooked it up to a 2 HP compressor and sure enough to it pulled vacuum, we didn't push it all the was but got up to at least 25 inch of mercury.

        have you used one of these? Do you know if it would do the job?

        thanks,

        David H
        As a navy Diver I used eductors to hold patches and coffer-dams against a ships hull, as they are fine for pulling a slight vacuum between ambient and the space you wish to lower pressure. But they are not suitable for de-gassing a mix like what we use for tool making.

        The educator is fine if your evacuating most of the air out of a volume tank, but degassing a mix requires at least 28.5 inches of Mercury. And that can only be done with a positive displacement pump. Bite the bullet and spring for a proper vacuum pump, Dave.
        Last edited by He Who Shall Not Be Named; 01-09-2017, 07:23 AM.
        "... well, that takes care of Jorgenson's theory!"

        Comment


        • #49
          Something Greg Sharpe used to do was do inverse vacuuming. He'd use a pressure cooker and an air pump. He'd put his molds in the cooker, seal it up and then pump it full of high pressure air. The excess pressure forced the bubbles in the molds to compress significantly.

          Comment


          • #50
            I saw a product the other day called "Bubble Buster". It is designed to reduce the surface tension on the moulded piece and allow all the trapped bubbles to disperse. Might be worth a try at $26.00.

            Comment


            • #51
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              Hello all,

              HWSNBN I have a question for you.

              As you know, I am developing a pump jet propulsor, my question is regarding the number of moulds I should make to cast the parts. I have posted two pics to show you what I mean.

              I decided to mould the front shroud support (the ring with 4 arms coming off it ) as a separate part from the main shroud( big round ring.) bottom photo. However with the rear stator assembly and its own shroud I cannot be sure that you have moulded these separately or as one piece , (top photos) after looking at heaps of your photo bucket images I m not sure. I am thinking through draft angles and air vents and the like and think it's possible but would love your thoughts on it. If I could it would save silicon, time and I could mould in nice filets around the supports, if not I will have to retain the slots and keeps it as a 'fit together afterwards' thing.

              i hope this makes sense..

              what are your thoughts?

              David H

              Comment


              • #52


                Originally posted by Davidh View Post
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                Hello all,

                HWSNBN I have a question for you.

                As you know, I am developing a pump jet propulsor, my question is regarding the number of moulds I should make to cast the parts. I have posted two pics to show you what I mean.

                I decided to mould the front shroud support (the ring with 4 arms coming off it ) as a separate part from the main shroud( big round ring.) bottom photo. However with the rear stator assembly and its own shroud I cannot be sure that you have moulded these separately or as one piece , (top photos) after looking at heaps of your photo bucket images I m not sure. I am thinking through draft angles and air vents and the like and think it's possible but would love your thoughts on it. If I could it would save silicon, time and I could mould in nice filets around the supports, if not I will have to retain the slots and keeps it as a 'fit together afterwards' thing.

                i hope this makes sense..

                what are your thoughts?

                David H
                Your making perfect sense there. And the answer is: both the forward and after portions of duct can be engineered to also posses their respective stators. The trick is to provide a 'bubble-catcher' ring at the top of the tools cavity. Like how I dressed out the masters for a 1/72 SEAWOLF pump-jets:

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                The bubble-catcher of course becomes an element of the casting, but is easily machined off the part on the lath. Here you see before-and-after bubble-catcher removal to the little pump-jets I produce for the Moebius SEAVIEW fittings kit.

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                I understand your worry, Dave: Will inclusion of the stator within the shroud lead to excessive bubble entrapment during the casting operation. Normally you are right, even if you employ centrifugal and/or pressure steps during the curing process. The bubble-catcher becomes a 'reservoir' to which air-bubbles can migrate to instead of the model part proper. A sacrificial element of the tools cavity, if you will.

                David




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

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