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  • He Who Shall Not Be Named
    replied
    Originally posted by george View Post
    Hello Again Sir:

    AS I know NOTHING about Vacuum chamber workings and JUST A LITTLE of pressure pot uses. I have to ask, how easy is it to work with Vacuum pressure system and what is the actual connections that are needed between the pump and the chamber?
    Maybe I`m wrong BUT it seems to me that the vacuum system is faster to work with than pressure pots.
    Where do you get the vacuum chamber? Does it have to be a glass object?



    Why are Diver's more bad-ass than astronauts? Because an astronaut will only see a maximum differential pressure of one atmosphere, but won't live long. A Diver will experience many multiples of that and (if he follows the tables) he'll be just fine.

    vacuum system plumbing is the same as pressurized systems, only less robust. In my world one-atmosphere is a fart in the wind. The only unique consideration with vacuum plumbing is to use flexible hoses that are of the non-collapsible type. Other than that, off the shelf fittings work fine in a vacuum system.

    pressurized pots are quicker to cycle through than vacuum assisted pours for cast resin production runs.

    No glass. Acrylic or Lexan bell-jar is what you want. Or a pressure pot pressed into vacuum service. Keep in mind: the larger the surface area, the more force applied (14.something per square inch!). Check Jewelry supply houses for the bell-jar (have oxygen at hand when you see the price). eBay is your friend. Vigor is one source for bell-jars.

    David

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  • george
    replied
    Hello Again Sir:

    AS I know NOTHING about Vacuum chamber workings and JUST A LITTLE of pressure pot uses. I have to ask, how easy is it to work with Vacuum pressure system and what is the actual connections that are needed between the pump and the chamber?
    Maybe I`m wrong BUT it seems to me that the vacuum system is faster to work with than pressure pots.
    Where do you get the vacuum chamber? Does it have to be a glass object?




    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by SSN687 View Post

    3 January 2020
    David,
    Thanks for information about the 1:72 scale US boats. I would like to ask Kevin a couple of questions about what he has in the que. Can you give me Kevin’s member id or email address.

    Thanks
    Ernie
    Nope. When he wants to go public he will. He monitors this forum and others. His call, Ernie.

    David

    Leave a comment:


  • SSN687
    replied
    Originally posted by He Who Shall Not Be Named View Post

    LOL. Sorry. I just like poking people with sharp sticks. Can't help it.

    There is hope for us on the horizon. Kevin Rimrodt is about done with his stand-alone shop and will begin kit production this year. And some 1/72nd projects are in the que.

    David
    3 January 2020
    David,
    Thanks for information about the 1:72 scale US boats. I would like to ask Kevin a couple of questions about what he has in the que. Can you give me Kevin’s member id or email address.

    Thanks
    Ernie

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by Davidh View Post
    Hello David,

    Thanks for your latest write up. You may remember months ago, how I asked you about Vacuum pumps and critical specs for pulling enough vacuum to de-gas silicon. You mention in your last write up how you quickly purchased from Harbour Freight a new ‘ cheaply low CFM vacuum pump’. I thought these pumps had to pull a relatively high CFM to do the job? I am confused. Could you give me the crucial specs for this pump? I have a chamber but Am still trying to get my head around the right pump.

    thanks

    David h
    I missed this post, David. Thanks for reminding me.

    The big issue with the vacuum pump, in our applications anyway, is not how quickly it can evacuate the work, but how pure a vacuum it can produce. So, the machine is chosen based on how close it can get to a perfect vacuum. Our minimum, for the work we do -- most of it will be de-airing either mold making rubber or pulling air from a resin filled tool -- is 38-inches of Mercury. That's the magic number. Inches of vacuum, not air evacuation rate.





    If the pump is too slow you buy a cheapy air-volume tank, some none-collapsible hose, a three-way valve. You hook it all up to the vacuum table. In operation you evacuate the tank before hand. It's then a simple matter to slam a vacuum to the work in seconds, not minutes. I have yet to encounter a job, even with this low CFM pump I'm currently using, that needs a volume tank buffer between pump and work.

    David

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  • Davidh
    replied
    Hello David,

    Once again, always great work. Could I have some clarity on the Vacuum pump questions from earlier?

    Thanks,

    David h

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    I took the cast resin sail parts and stuck them together. Assembly was straight forward: the three internal platforms were glued within the sail, the sail top piece (the one with the openings through which the raised mast fairings project) glued atop the main structure, and two holes drilled and tapped at the bottom platform to accept the screws that would pass up through the upper hull to secure the sail in place.



    A simple poster-board alignment jig insured I sanded the base of the sail so it would sit level atop the upper hull. Any significant gaps between sail top and sail proper were filled with CA and flashed to hardness with either a sprinkling of baking soda or a good wetting with 'accelerator', followed by careful file work.







    The engraved lines on the kits upper hull were not up to my standard: though an appreciated attempt the hull featured both non-skid and waterline cheat-lines -- these were way too deep and had to be filled to the point were once the model is painted, those cheat-lines will be barely perceptible. I spent the entire day using circular cutters and scratch awls to dress up the original work. Lots of putty to fill dings errors and overly aggressive cheat-lines. Once dry the excess putty was knocked down through some spot wet-sanding, followed by careful re-scribing.






    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by 598602G View Post
    I am making the molds to sell kits for a 1/72 688. How about those Happy New Year apples? Should be done with molds in 2 weeks.
    That's good news, Tim. Lots of boat sailors out there who served on those cramped pencils. Should be a market out there to exploit. Other than an abundance of fresh water and no diesel stench the LA's had worse habitability than the GUPPY's. Glad I never served on them.

    David

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  • george
    replied
    O.K Then Thank You for your confirmation. And Thanks for the lessons.

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by george View Post
    Hello Sir
    Please excuse some OLD questions. In your 1/72 torpedo you mentioned long before that the brass core you used was 7/32" solid but it`s finished O.D would be 0.279" and your 1/96 brass core 3/16" so it`s O.D would be 0.210". Is that a strong enough wall thickness to handle to run gas torpedoes safely?
    It worked for me. The launcher is designed so that the weapon is charged and maintained within the tube before launching. The tube itself is insurance against fragmentation should a weapon explode under pressure.





    David

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  • george
    replied
    Hello Sir
    Please excuse some OLD questions. In your 1/72 torpedo you mentioned long before that the brass core you used was 7/32" solid but it`s finished O.D would be 0.279" and your 1/96 brass core 3/16" so it`s O.D would be 0.210". Is that a strong enough wall thickness to handle to run gas torpedoes safely?

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by SSN687 View Post
    1 January 2020
    David and Ellie,
    Happy New Year. Stop teasing me with these 1:72 scale US boats that are no longer in production.

    Thanks
    Ernie
    LOL. Sorry. I just like poking people with sharp sticks. Can't help it.

    There is hope for us on the horizon. Kevin Rimrodt is about done with his stand-alone shop and will begin kit production this year. And some 1/72nd projects are in the que.

    David

    Leave a comment:


  • 598602G
    replied
    I am making the molds to sell kits for a 1/72 688. How about those Happy New Year apples? Should be done with molds in 2 weeks.

    Leave a comment:


  • SSN687
    replied
    1 January 2020
    David and Ellie,
    Happy New Year. Stop teasing me with these 1:72 scale US boats that are no longer in production.

    Thanks
    Ernie

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by george View Post
    Hello

    Happy New Year first.

    Now given a choice, either or which would you use for making castings/molds? Pressure Pot OR Vacuum chamber and why?

    Thanks for the lessons
    I typically use a vacuum to extract air-bubbles from a mix of tool making rubber as air invariably gets folded into the mix.



    Bubbles, which if retained in the mix, present as voids that collapse slightly under pressure (during the pressure casting process, which I prefer) resulting in 'dimples' spoiling the surface of the cast resin part.
    The rubber mix, before it changes state, is briefly subjected to a hard the vacuum (at least 28 inches of Mercury) to enlarge the bubbles to a size where they rapidly rise to the surface of the mix, pop, and the air extracted by the vacuum pump.



    On occasion I will employ vacuum to assist in the fill of thin walled casting tools. Like this:







    On rare occasions I will us air pressure to crush bubbles back into solution when processing RTV rubber into a tool, but that means holding the pressure for the length of the state change, which can be half-a-day. Dumb.

    Pressure is almost always used to crush bubbles in quick curing resin parts. Typically one or two atmosphere (gauge). Pressurization time is about twenty-minutes. Most of my pressure-pots are commercially available paint-pots that can be had for about a hundred-bucks each. I've also have on hand custom pots I had manufactured for the bigger projects around here.








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