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  • He Who Shall Not Be Named
    replied
    OK, Dave, it took a few days of part-time work, but here's the second part of the information you asked for, this one dealing with GRP hull fabrication tooling. Enjoy.

    TOOLS FOR GRP LAY-UP (HULL MAKING)

    Fiberglass hulls are laid-up within large multi-part tools (called molds in some circles). Typically a set of tools comprises an upper-lower or left-right set for the hull and a left-right set for the sail. Regardless of tool type, the end game is the same: production of thin walled, strong fiberglass structures.

    Glass reinforced plastic (GRP) hulls and sails are preferred over other substrates for three main reasons:

    1. GRP's very thin wall thickness -- the less water the above waterline structures displace, the less ballast tank you need to get the model up to the designed waterline (only a consideration for wet-hull type r/c submarines)

    2. strength

    3. the ability of the initial gel-coat laminate to capture the most complicated of detail within the tools cavity without the need to resort to exotic pressure differential equipment (pressure/vacuum vessel)

    The hull-sail tooling can be GRP hard-shell, cement, a hybrid of rubber and GRP (mother-glove mold), clay, cuttlefish bone, heavily filled resin, or any number of other materials that can capture, in negative, the form of a master (pattern, or model if you will).

    However, this discussion will be limited to the cement, GRP hard-shell, and hybrid mother-glove mold type tools.

    GRP HARD-SHELL TOOL AND SPACE STATION TORUS GRP PART LAY-UP

    The traditional (most often used) type is the GRP hard-shell tool. It's both cheap and easy to make.

    (Surprisingly, I can't find any pictures in my massive collection of pictures of a hard-shell GRP tool applicable to submarines. But, as a stand-in I present these shots showing the fabrication of the master, tool, and model parts of a 'wheel' type space station model, based on an effects miniature used in the old George Pal movie, The Conquest of Space).

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    The first picture is of the finished space-station model fabricated principally from GRP -- those parts fabricated in a hard-shell GRP tool of unique form. The second shot is a frame enlargement from the actual film, The Conquest of Space. A magnificent movie that does not get the credit it deserves.

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    Though a bit outside the preview of this discussion, I thought you would like to see how I gave form to the master of the torus. If you will, the 'hull' of the space station. The process is called screeding -- giving form to a pliable mass, in this case warm modeling clay initially, followed by an over-coat of uncured automotive two-part filler.

    A circular screeding blade swings around a fixed pivot over the mold board. The blade gives form (half a torus) to the clay as it's pushed in a circle about the mold board -- this is described as circular screeding.

    Note the larger semi-circular blade at the top. This one is used to give form to automotive filler, which goes over the clay. The clay is there to reduce the amount of filler needed to make the torus half-master. The filler formed spoke elements were linearly screeded on another board and transferred to the torus to make up the space-station half-master. The central hemisphere was turned from solid Renshape.

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    The space-station master and mold board was first given several coats of wax, buffing between coats. Finally, the entire master and mold board was spray coated with polyvinyl alcohol (PVA), a water soluble film that serves as a barrier between the soon to be applied epoxy laminating resin and the waxed surface of the master and mold board. This type barrier is referred to as a mold-release.

    This mold-release step, and the products used, are the same as used between the submarine master and its mold board and the hard-shell tool (mold) that will be laid up over them. And, conveniently, the same wax and PVA are used as part-release agents forming a barrier between tool and GRP model parts.

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    In this shot you see the GRP space station hard-shell tool under a space-station GRP part. The broken popsicle sticks and hammer were used to pry the GRP part off the GRP tool. An ugly affair but no damage resulted during the 'liberation' effort. Once a second GRP part is made, they are trimmed to the flange face of the tool and bonded together forming the complete torus and spoke assembly that represents the space stations hull.

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    With the exception of the dumb-bell central parts and white-metal mirror support pieces, the entire model was constructed of very thin walled GRP.

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    How thick (wall thickness) should the r/c submarine GRP hull be? We want it thick enough to have the strength to survive normal handling, and moderate collision forces. But we don't want it so thick that the structure above the models waterline displaces an unreasonable amount of water. Balancing these two requirement, strength and displacement takes some though and experiment.

    My considerable experience in the field has taught me to keep the nominal wall thickness of a GRP hull at about 1/16" - 1/8" thick. 1/16"thick for small models up to 50" in length. And 3/32" - 1/8" thick for the longer model hulls.

    The thickness of the gel-coat and number and weights of fiberglass cloth/mat laminates is driven by the geometric complexity of the tool cavity. The more complicated the geometry, the thicker the gel-coat(s), the more laminates of light-weight weaved glass. A simple hull like the DELPHIN only required one gel-coat, and two laminates of 15-ounce glass mat.

    Above is a test I did for a simple of geometry 70" long submarine hull. The nominal wall thickness was to be 1/8", built up from the minimum number of laminates I could without having the saturated glass bunch up and produce the dreaded air voids. Several test samples were laid up from scrap material into the most complicated section of the tool -- the objective to work in the gel-coat and glass laminates, finding the heaviest glass weave and mat that would wet out completely without producing air voids. On this particular model I found that a gel-coat, followed by one laminate of 4-ounce cloth, a laminate of 10-ounce cloth, and a laminate of 15-ounce mat produced a GRP structure able to produce void free parts and achieve the 1/8" wall thickness goal. This established, the required number, weight, and type fiber glass sheets were cut out, and work laying up the GRP hull halves began.

    CEMENT TOOL AND HULL LAY-UP

    Darrin Hataway -- an excellent professional model builder, and responsible for several of the excellent OTW hull kits -- gave me an old cement tool he made for a large scale model of the WW-2 era German DELPHIN one-man submarine. This tool was made from a fine grained type cement, sometimes sold as 'hydro-stone' or dental cement. This type mold making material is good for producing tools whose surface is not festooned with high relief engraved lines or plating, as the cement is relatively weak in shear and such details would break off with usage. However, as a quick-and-dirty, cheaply made tool for un-detailed GRP hull fabrication, it's perfect. Owing to the rigid nature of the material there can be no negative draft to the cavities, and zero draft is to be avoided or you'll never be able to de-mold the laid up GRP part after lay-up.

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    I laid up the upper and lower GRP hull pieces in the tools. The two hull parts were then cut (lower hull bow and upper hull stern) and re-assembled and glassed back together to achieve the Z-cut so favored by those assembling GRP type r/c submarines of the wet-hull type.

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    Darrin's tools arrived already saturated with part-release wax. It was a simple matter to lay down a fresh coat of wax, buff it out, and spray in three coats of PVA barrier film -- this readied the tools for gel-coat and GRP lay-up.

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    Gel-coat is simply a thickened laminating resin, laid down without glass re-enforcement. It's the first layer of material to go into the tools cavities that forms the eventual model part. Therefore the gel-coat becomes the surface of the GRP model part. You want this layer (the gel-coat) to be strong, and able to wet out every portion of the tools cavities -- the primary job of the gel-coat is to capture all the details present in the tools cavity and to produce a softened, curved (fillet) transition between sharply angles projections within the cavity, over which the laminations of fiberglass cloth and mat will go. Sometimes multiple coats of gel-coat are applied to areas of sharp relief to further fillet the area so subsequent laminations of glass won't be stressed to the point of de-laminating and producing voids.

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    A simple hull form, like the DELPHIN, results in hull tools that permits laying in relatively heavy material over the minimal thickness of gel-coat. Glass mat or weaved cloth is measured by weight of the square-yard. In this case I went right in there with 10-ounce weaved cloth, three layers (laminates).

    For economies sake -- particularly if you have many laminates to build up and/or you are going to make multiple copies of GRP parts -- it's a good practice to trim one piece of the glass cloth to make a tight conformal fit within the tool, mark off where the cloth meets the tools flange face, remove it, set it over a big piece of poster-board, and trace its outline with one-inch more boarder for safeties sake. You can see the DELPHIN's orange poster board glass marking template in foreground -- used to cut to mark out all subsequent glass cloth pieces for cutting. This saves material and time doing it this way.

    GRP HARD-SHELL TOOL AND HULL AND SAIL LAY-UP

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    My boss, Mr. Caswell, purchased tooling for a 1/72 M-1 submarine kit and asked me to evaluate it by laying up a hull for him and me. This tooling is of the classic GRP hard-shell type. However, a bit unusual in that there is no egg-crate support structure backing to prevent these long items from warping over time. But, I found to my surprise that the GRP model parts I pulled from these tools fit near perfectly. So, no egg-crating, no problem.

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    Once the initial fit of glass cloth bits to fit the tool is made and that cloth laid out over some pink poster board (pink???) and the templates made, the templates are used to cut out all the pieces of cloth and mat needed to achieve a full laminate.

    The perfect cutting tool for glass fiber sheet is a pizza-knife over a plywood cutting board. You lay the cloth over the cutting board, use the template to mark out the outline of the cloth/mat, and then cut the laminate out with the circular-knife/pizza-knife. The knife is very easy to steer and won't pull and snag the tough glass material as an X-Acto blade or scissors would.

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    Here's the M-1 tooling. Whoever did this work is damn good at it: thick, wide flanges; good tool design (optional superstructure stand-alone tool or superstructure incorporated in the hull tools); and the sail tools were indexed to clamp together permitting me to bond the two halves together in-tool. A joy to work with!

    Here you see all tooling after receiving their third spray coating of PVA. I use the heat gun between layers of PVA to speed up the work.

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    These tools came to us already built up with wax, so all I had to do was lay down and buff up my own wax layer, spray on three coats of PVA and get to the gel-coat. Now, there are various fillers you can add to laminating resin (by the way, I like the West System laminating epoxy laminating resins -- I use the 'fast' one) to thicken it up so it will build fillet between harsh angled items in the tool cavity. On the M-1 there are near zero draft angles between the hull and superstructure, and the hull and deep keel -- these areas required more than one coat of gel-coat to soften their edges. If you fail to do this, even the lightest fiberglass cloth will bunch up and leave awful air voids.

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    The most difficult glass work is the sail. Lots of gel-coat, and many layers of 4-ounce cloth, cut into small bits so the class could negotiate the tight fillets without bunching.

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    Once the GRP sail part had cured hard, it was popped out of its tool and the excess GRP that extended past the flange line (obvious on the parts, so no need to mark it while still in the tool) ground off. The flange and cavities of the two tool haves were then waxed up in preparation of the next step.

    The GRP sail halves were re-inserted into their tools, and the two indexed tools assembled, putting the edges of the GRP parts up tight against one another and in perfect registration. It was then a simple matter of wetting the seam area from the inside of the part and sticking a strip of glass in there to back up the seam, turning the assembly into a one-piece sail. Pretty slick took design!

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    The open sail tool with the three securing bolts used to hold the assembled tool halves together as the GRP sail halves are bonded into one unit.

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    Between laminates of gel-coat, glass cloth and/or mat I sand the surface of the hardened laminate while it's in the tool to knock down bumps and give plenty of tooth for the next layer of resin saturated glass to grab onto. There is no cohesion at work between a cured hard surface bonded with epoxy or polyester resin to the next laminate, so the agent of 'stick' is strictly mechanical and adhesive in nature.

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    A completed M-1 GRP hull half part next to the tool that gave it form.
    Attached Files

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  • Albion
    replied
    Nice game. Glad you tube wasn't around then.

    Question Mike, I assume airlines wouldn't like me putting casting resin or RTv type products in my luggage?

    Leave a comment:


  • Albion
    replied
    Nice game. Glad you tube wasn't around then.

    Question Mike, I assume airlines wouldn't like me putting casting resin or RTv type products in my luggage?

    Leave a comment:


  • Kazzer
    replied
    Originally posted by He Who Shall Not Be Named
    Yes, my motivational techniques are good. I learned when I was part of the American combat submarine culture. A culture that, long before Lucas used the line, personified the concept, there is no try. There is only do. Perform to expectations, or suffer. It's called, 'qualification' and the stick is hazing. In the old days of sail it was called 'learning the ropes'. Until recently, in the crafts, it was the apprentice-journeyman-master assignment of status. All successful forms of motivation and class establishment-advancement employ the carrot and stick.
    M
    Hazing eh? In the US Navy eh? I wasn't much impressed when I went to dinner with friends of mine and we discussed the lack of greens on his dinner plate. He was an Executive Officer i/c a minesweeper (Sounded like second in command). At Navy College they were made to eat a huge plate of Brussels Sprouts and suffer the inconveniences thereafter. Consequently he couldn't stand even the smell of them. Poor baby was traumatised for life.

    I then explained how my dad went through his hazing on his first submarine. All the new men sat around the dining table/bench, intently waiting, and two seniors entered the cramped room.

    "We're going to play 'Freckles'! Anyone ever played Freckles?" No one had, so the scene was set.
    One senior man jumped onto the table, dropped his pants, and deposited a large pile of do-da right in the middle of the table. There were many astonished faces, staring at this warm, steamy pile! The seniors were contented with the effort, and so the other senior said, "Right men! Look closely! They all moved closer, and then suddenly, the senior's large hard flew down and whacked the pile, splattering 'freckles' everywhere.

    "There! That's how you play Freckles! Now clean this bloody mess up."

    After that, there were a lot less squeamish men on board that submarine.

    Sprouts or Freckles? Depends which navy you were in! (Expecting a barrage of freckles coming my way!)

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  • Kazzer
    replied
    Originally posted by george
    Hello again


    Have you ever thought about a Tool/raw material how to video?

    Thanks Again

    George
    George! NO! NO! and THRICE NO! I'm the one that has to edit his 'movies'! He's got an obsession with sanding, and will let the camera run for hours while he's sanding the most boring part of a boat. And he drones on, and on, and covers the same thing six times!

    We're not doing it! No! NO-no-no!

    Arghhhhh!

    Have I got to come over the border to sort you out? It'll get ugly!

    Leave a comment:


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

    Yikes ! I will have to read and reread MORE and think hard before I ask again. I like your motivational technique.

    Have you ever thought about a Tool/raw material how to video?

    Thanks Again

    George
    I try to keep it humorous, but I do see way too much useless asking of questions by the same people, people who seem to do nothing with the information handed to them. I'm a results sort of guy, and when I see non-performance from someone who has stated a goal but refuses to make the real, tangible effort to achieve the goal, then I see a guy who has WASTED MY PRECIOUS TIME! And time is the one thing that when it's gone, you can't get it back.

    I so cherish CLARITY. I speak plain; I convey meaning directly, and bluntly, so that those hearing me will KNOW what I mean. CHAOS is happy-talk and smiley emoticons. Clarity is achieved through plain speaking. Display of purpose is actions, not words.

    Yes, my motivational techniques are good. I learned when I was part of the American combat submarine culture. A culture that, long before Lucas used the line, personified the concept, there is no try. There is only do. Perform to expectations, or suffer. It's called, 'qualification' and the stick is hazing. In the old days of sail it was called 'learning the ropes'. Until recently, in the crafts, it was the apprentice-journeyman-master assignment of status. All successful forms of motivation and class establishment-advancement employ the carrot and stick.

    There is no equality in life. There are the elites and the non-elites. One should strive to be an elite. There is no 'fair'. There is only accomplishment or non-accomplishment.

    My world is black and white. No grey. I'm productive as a result. Most are not.

    I've done plenty of video, a lot of it on youtube, George. Go find it. And check out Culttvman, lots of my stuff there as well.

    M

    Leave a comment:


  • george
    replied
    Hello again

    Yikes ! I will have to read and reread MORE and think hard before I ask again. I like your motivational technique.

    Have you ever thought about a Tool/raw material how to video?

    Thanks Again

    George

    Leave a comment:


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

    Question to HWSNBN David

    First Thank You for posting your tool making instructional lessons. I would like to ask you about your Alumilite slow-cure polyurethane casting resin that you use now. If I remember, a LONG TIME AGO you used the Alumilite yellow brand and had discovered over a few years that the product shrunk slightly, in WTC end caps that was an issue.

    Does this version have better properties OR how do you work to avoid that?

    Again Thanks for the Lessons of Tool building and your techniques.

    George
    My pleasure, George.

    That was the BJB 610 casting resin, if memory serves. I stopped using that over ten years ago when I discovered the Alumilite product line.

    I've found that after 30 days (the 'green' period) the Alumilite has shrunk all it's going to. The 610 just kept creeping away.

    I have no problem giving pointers to the guys out there who actually do something with my little pearls of wisdom. Ask away.

    But ... remember this! There are such things as stupid questions. Ask one and I'll hand you your still beating heart!

    M

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  • george
    replied
    Hello

    Question to HWSNBN David

    First Thank You for posting your tool making instructional lessons. I would like to ask you about your Alumilite slow-cure polyurethane casting resin that you use now. If I remember, a LONG TIME AGO you used the Alumilite yellow brand and had discovered over a few years that the product shrunk slightly, in WTC end caps that was an issue.

    Does this version have better properties OR how do you work to avoid that?

    Again Thanks for the Lessons of Tool building and your techniques.

    George

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by Davidh
    O.k dave,

    looking forward to it.

    dave h
    It's David. Not Dave ...

    ... ******!

    M

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  • Davidh
    replied
    O.k dave,

    looking forward to it.

    dave h

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    I'm delighted to help you, Dave.

    You plowed ahead and got your RESOLUTION done. That tells me volumes about you (most of it good). It's a joy to help someone who clearly has the will and hands to see a project through to completion. I'm at your disposal, sir.

    GRP hull tool making next. I've started in on the article, but need a few more days to complete it, so be patient.

    M

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  • Davidh
    replied
    Hello Dave,

    Thankyou for spending your time imparting this gold to us. I really appreciate it. I realised that tooling is a big part of what you do/ we do however it as a subject does'nt get a lot of air time and yet it is make or break for the end result.

    I went into the unknown 2 weeks ago when I bought my first tin of silicon. I realised that to really do the kinda stuff you do at that level required it. There was not much in the store ( literally at my local supplier a good hours drive away) all they had was 3481 base. I guess they'd sell a general purpose silicon for the widest application.

    My my first mould barely set after three days, not enough hardener, however as you can see from the pics I've learnt a lot in a fortnight. I love the White fluffy cheesecake like look. Makes me want to bite into it.....

    ok enough of that disturbing.. Anyway I'm a convert and asked myself why I wasn't using this stuff years ago. I am going to build a couple of kits of the Resolution so we are only talking very low volume use of the moulds. Not 300!

    i am really interested in how you do a whole hull RTV mould with grp backing. I would love some pics of how you construct this although I have already been guessing the process. I am tempted.

    i don't know why this pic


    regards,

    david h
    Attached Files
    Last edited by Davidh; 06-25-2015, 05:31 AM.

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  • He Who Shall Not Be Named
    replied
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ID:	98901 Research was extensive and netted a lot of good dope. The result were finally detailed masters such as zinc anodes (three different types, no less!); crew figures; masts; deck fittings; ladders; anchor; propellers; antennas; and sail detail items. In fact, there were so many eventual white-metal parts that I was compelled to make two spin-casting tools -- I'll just cover one of them during this presentation.

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ID:	98900 The diameter of the tool is driven by the spin-casting machine -- in my case an old blood-separation centrafuge -- a rubber disc of about eight-inches diameter. I first mock-up the placement of the masters -- used to give form to the RTV tool cavities later -- onto three concentric penciled circles. The outer circle denotes the peremeter of the tool; the middle circle denotes the center of mass of the master; and the inner circle is the warning track, where there is not enough force generated by rotation to adiquatly fill the tool voids with metal. I also work to diametrically place like volume masters, so as to not get the tool too out of ballance as the metal is poured into the sprue.

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ID:	98902 The masters are transferred from the mock-up poster-board and pushed into a clay-faced mold-board. Note the inclusion of a central sprue, runners, and bolt cavity cores. A masking-tape damn will be wrapped around the perimeter of the mold-board and catalyzed RTV rubber poured over the imbedded masters and cores creating the first half of the two-part spin-casting tool.

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ID:	98904 I use the same relatively hard, high-temperature tolerant RTV silicon mold making rubber, BJB's TC-5050 for all my non-hull making rubber tooling. The stuff is measured, catalyzed (done with vigorous mixing that invariably introduces air-bubbles in the mix), de-aired (expanding and evacuating the air-bubbles by subjecting the mix to a near perfect vacuum), and the bubble-free mix poured over the prepared masters.

    If any air-bubbles remained in the mix the air within would expand as the tool halves get hot, distorting the rubber, ruining the form of the cast metal part. An alternative to the vacuum de-airing is the practice of exposing the mix, as it transitions from liquid to solid state, to at least two-atmospheres absolute -- this crushes the air-bubbles and puts the gas into solution. Vacuum or pressure, you have to get the air-bubbles out or the tool is useless!
    Oh, did I mention ... RTV rubber is expensive ****! So, get it right the first time.

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ID:	98905 Just a quick aside: To insure a perfect capture in metal of the detail and finish of the tool cavity you have to insure that there is no water within the tools cavity. At normal humidity there is water in there, so you use a hydroscopic powder such as Talk to absorb it. Just before using the tool for metal casting -- here you see an open faced RTV silicon lead weight making tool -- Talc is dusted into the cavities and the excess banged out and onto the floor, and the metal poured.

    Same for the two part disc type metal casting tool: the halves are dusted, excess Talc banged out, the tool assembled, clamped down onto the centrifuge bed, spun up, and metal poured.

    And make sure you've got Talc and not corn-starch!!!! Guess why I bring that up?....

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ID:	98906 The spin-casting tool bolted down onto the bed of the spin-casting machine. Note the use of a Dumas speed controller to set the ideal spin for metal casting -- each tool has an 'ideal' speed of rotation, found through experiment. This part of the game is more art than craft. To the right is the metal melting pot-pouring ladle. Behind it is some of the 'plumbers solder' I use for metal casting. For clarity I've omitted the splash-shield -- an item you must use or you'll burn your titties off!

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ID:	98907 And the FOXTROT metal pieces; the end game. Trees of metal parts ready to be snipped off their runners and bagged.
    Metal casting is a very quick production method -- an important consideration in a business where time is money. Also, there are some model parts, owing to the stresses they will be subject to, that are better produced from metal than plastic.

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ID:	98912 Another use of spin-casting is to drive metal or resin into very thin sectioned cavities, such as the blades of this OTW 1/100 VANGUARD pump-jet, white-metal rotor. With this tool two forms of force are used to drive the molten metal into the tools cavities: gravity and centrifugal force. The tall sprue -- by virtue of its vertical height -- produces a pressure head forcing the metal into the bottom cavities; and centrifugal force which works to drive the metal outward from the center of rotation into the very thin blade cavities.
    There are numerous ways to skin the cat at the disposal of the competent model-builder! The trick is ... talking the cat into cooperating.

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ID:	98911 Another example of employing the spin-casting technique to achieve a complete fill of a difficult tools cavities with resin is exemplified by this 1/48 SEAWOLF pump-jet I was commissioned to build for a customer. This monster required the use of five, large, disc-type tools for the pre-swirl stator-hub; post- swirl stator-fairing bullet; after duct; forward duct; and ringed rotor.

    RTV SILICON RUBBER TOOLS THAT PRODUCE POLYURETHANE RESIN PARTS

    RTV silicon rubber tools for gravity assisted polyurethane resin casting differ in that the tool design has to allow for the escape of air out of the tool cavities as its displaced by the filling resin.

    (provision of vent channeling in disc-type tools subjected to centrifugal forces is not necessary as when the metal or resin is introduced the force applied to it and the mass of the liquid is enough to distort the flange-face of the two-part tool, causing the escaping air to burp out as the metal or resin rushes into the cavities -- the same mechanism at work as goes on within the metal tool of an industrial injection forming machine, the same ones that produce the traditional plastic model kits).

    Since gravity is the agent of resin motion within the tool, we are compelled to make the sprue channel as tall as possible, and to provide vent channels from each cavity to permit the easy escape of displaced air. A failed tool design is one that produces incomplete fills of the cavities, resulting in 'short-shots', i.e. parts that are incomplete; partially cast. This problem usually fixed by simply enlarging the sprue and/or vent channeling.

    Tool design is embedded in my DNA, I can do it in my sleep. Yes, I'm that good at it. Study the pictures and you'll get a lot of insight on proper tool design from one of the world's best.

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ID:	98915 The majority of the resin casting I do is the manufacture of machines. Items that do useful work. All of the bulkheads and some of the discrete parts that go into my Sub-drivers (SD's) are cast from polyurethane resin. The above, assembled 2.5" diameter SAS type SD is but one example of our use of polyurethane resin parts. And here is a shot of the different 3.5" motor bulkheads produced here.
    Resin parts are robust, easily machined, are excellent insulators, chemically resistant to all but the most aggressive acids and alkyds, and do not suffer significant alteration of their physical properties over time.

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ID:	98921 All of our fittings kits -- after-market packages that contain parts to convert a static plastic model submarine kit into a practical r/c submarine -- employ cast resin pieces. At one time, as D&E Miniatures (before our association with the Caswell company) we produced resin kits for the SF and Space modeling communities as well as 1/192 resin kits of the LA and STURGEON class submarines. Examples of model parts produced using the resin casting technique are presented here.

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ID:	98922 Your typical RTV silicon rubber tool for gravity casting looks like this. The two halves of the tool, held together between two stout wooden strongbacks, clamped tightly with either rubber bands or pass-through bolts.

    The resin of choice is Alumilite slow-cure polyurethane casting resin. As is it cures to a tan color. But, for proprietary reasons, Caswell-Merriman dopes the resin to a blue color. Other than that, it's the same stuff sold in the hobby-shops (at a ridiculous mark-up!).

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ID:	98923 Talc was used with metal casting as a hydroscopic water-catcher. In resin casting Talc is used to coat the tool cavities after the part-release spray is applied. In this application talk acts to wick in the resin to corners and small cross-section cavities that otherwise might not fill completely with resin during the pour. Here you see a bunch of SD bulkhead tools being prepared for casting. Note the talc, Mann-200 part-release (also the preferred mold-release agent during tool fabrication), powdered tool halves, rubber bands, and strong backs. Unlike metal casting, this is a situation where you can substitute corn-starch if you're too cheap to spring for Talc.

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ID:	98925 It's not enough to pour the catalyzed resin into the tool and leave it to sit as the resin changes state to a solid. No. You have to pressurize the mix as it changes state. This to crush any bubbles introduced during mixing and to crush any void bubbles in the cavities into the solution. Two atmospheres of pressure will do it (30 PSIG). That's two Bars for you European types. My pressure pots are nasty old paint spray pots modified for this type work. Today I get mine from Harbor Freight.

    You prepare the tool, button it up and make up the strongbacks, pour catalyzed resin into the sprue holes, place the tools into the pressure pot and button it up, make up the air hose and pressurize the pot to 30 PSIG and wait for the mix to harden. De-mold the parts and repeat the cycle.
    We're hav'n fun now!

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ID:	98927 In the interest of economy and time it's a good idea to gang as many cavities into a tool as you can -- why go through multiple preparation and other tooling tasks when you can go through the steps one time? Such is the case with this 2.5" SD set of parts tool. All the cast resin items to make up a complete SD in one easy to use tool.
    Time is money!

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ID:	98930 I'll close the RTV silicon rubber tool for resin casting talk with a bit about inserts and cores -- used to encapsulate non-resin parts within the resin part and produce bores.

    A good example are these SD internal ballast bulkheads which require a horizontal bore hole to pass the ballast tank conduit tube, and in the middle of that bore to partially encapsulate a sealing o-ring or quad-ring. The packing making watertight the union between bulkhead and conduit tube.

    A brass core is machined to fit within the tool cavity, a slight groove in the middle of the core accepts the packing ring which will be partially encapsulated within the resin bulkhead. The packing equipped core is set into the tool during assembly, the resin pored, and the resulting cast resin bulkhead parts is popped out, and the core pulled free, leaving the partially embedded packing ring within the bore, The inboard face of the packing making the seal between bulkhead and conduit tube, which connects the forward and after dry spaces of the Sub-driver.

    A similar insert-core process is employed to make our line of pushrod seals.


    Don't panic Dave, I'll get to the hull tooling later this week ... for now I need a breather, pal.
    David

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  • He Who Shall Not Be Named
    replied
    Originally posted by Davidh
    Hi Dave, and anyone else who wants to contribute,..

    After building Resolution and doing a lot of looking into silicon RTV moulds I have finally dived in the deep end and use RTV as I have wanted to do castings of hydroplanes etc..

    i have looked very carefully at all the pics you've put up of your green and Blue Rtv moulds as well as Youtube and have started doing similar for the Resolutions control surfaces. I haven't done the whole spruce and vent set up yet, want to get experience just with the basic castings.

    I get the impression from your workshop that silicon moulds are probably the most common form of tooling that you develop for fabricating parts, is this right? Do you still use hard shell (grp) moulds for hulls? I would consider using silicon moulds for larger parts if they give better fidelity but just don't know enough about how wobbly a large mould like that would be and making sure it was supported enough.

    what kind of lifecycle do you get out of your silicon moulds? Any particular hints in looking after them or specific things I should keep an eye on whilst making them and or using them?

    i see that these moulds are really wobbly. You back them with what looks like a piece of chipboard. Is there the concern that you may have a little give in the silicon mould and it may slightly distort the piece coming out of it?

    Out of curiosity you must have made hundreds of these moulds, would that be correct?

    the skills you freely impart are fantastic, I just wonder whether more discussion about tooling design and use would complement the other skills that you teach. I would certainly find it beneficial.

    thanks Dave,


    David H

    Hey, Dave! Good to hear from you again. So .... you want some pointers on tool making, huh?! Careful what you ask for, pal! I'll split the discussion into two parts. The first part (this one) is on: resin and metal RTV tool making -- the same rubber can handle both resin and low-temperature metal).

    [Later, I'll give you the low-down on GRP hull tool making and use. But, here's a teaser: I prefer not to use hard-shell (GRP) tools to make hulls -- I use a highly detailed RTV rubber 'glove' mold to give the detailed form to the hull part, and a stiffening 'mother' mold element to hold the rubber element in proper registration during the lay-up process of the hull part].

    You're observation that the most numerous type reproduction tools I have in this shop are RTV silicon rubber is most correct. I not only have tools in the shop you've seen in pictures, I also have a shed full of the tools that are least active these day. As a side-note: the 'garage sale' WTC's Mr. Caswell has been offering in the catalog are pieces formed from some of the old, no longer used tools I had kicking around here and was thinking of throwing out before Mike intervened.
    But, first, let's clear the air ...

    A word of caution (you know this already, Dave, so I'm shouting at those looking over our shoulders):

    Don't make tools off of other peoples work without their permission. You don't have their permission? Then DON'T COPY THEIR WORK!!!!! You don't have the skill or time to do your own master work; or purchase the services of a pattern-maker or secure permission of the property owner? Then learn those skills! Don't steal someone else's work!

    You need a duplicate of a kit part, then BUY another kit! Or, secure the permission of the property owner to cast duplicates. The kit you need additional parts from is out of production? That does not give you license to copy it -- that kit is still the property of someone or some corporate entity ... it's not YOURS!

    Don't hit me with that 'fair-use' crap. If I knock you down, take your wallet and run off, am I making fair-use of your money? NO! It was your money, not mine!
    Don't be a thief! I'm not teaching you this stuff so you can rip someone off.

    There!


    You ask how long the RTV silicon rubber tools last, Dave. The following is in regard to solid part casting in these tools:

    Back in the 70's I was getting only 40-80 pulls from a tool before it started tearing up. Three things changed to vastly increase the cycle life. First was an improvement in the silicon chemistry itself. Second, the availability of the more benign polyurethane resins as the substrate of choice for 'resin' parts. And, finally, the introduction of a superior part-release spray (Mann 200) and the discovery that a Talc coating not only enhanced part fidelity, but also extended tool life -- these two part-release agents working to improve cavity fill and to act as a barrier between the resin and the silicon rubber. Today, if I don't get at least 80 pulls from a tool, something went terribly wrong. Now, all that was about resin casting tools. Metal tools are something else.

    I've found that the tool-life of JBJ's, TC-5050 RTV silicon rubber, when used to produce cast white-metal parts, seems to be unlimited. My old 1/60 ALBACORE tool is still going strong, pooping out near perfect metal parts after nearly 300 cycles. And that tool is about twenty years old! So, Dave, there you have it .... tool life over time and usable cycles is much better than it used to be.

    RTV SILICON TOOL MAKING AND DESIGN FOR PRODUCTION OF METAL AND 'SPECIAL' RESIN PARTS

    There are two common means of injecting the molten metal (white-metal: a little Antimony and a lot of Tin) or catalyzed resin (polyurethane) into the tool cavities: gravity and centrifugal force.

    Typically, gravity is employed for resin casting, and some metal casting (providing there is a significant height between sprue opening and cavity); centrifugal force for metal casting (and, on rare occasion, for resin casting).

    These two methods dictate two different type tool construction: the tool takes the form of a two-part disc for metal casting. And typically two tall tool halves for resin casting -- the higher the sprue over the cavities, the more pressure applied (pressure head) to drive the resin into the cavities. The one thing the tools have in common is the type rubber their made of. I use the high-temperature (up to 500-degree continuous)tolerant, room temperature vulcanizing (RTV) silicon mold-making rubber, product code TC-5050, produced by the BJB company.

    Dave: you speak to the 'wobbly' nature of the rubber tools. Yes, they are flexible. Elastic if you well. But the degree of flexibility is a function of what type RTV rubber you purchase -- it can range from the stiffness of tanned leather to mush. The TC-5050 rubber I use is somewhere between the two with a Shore hardness of 50.

    I recommend you stick with the Platinum curing type as it will last longer over time than the cheaper Tin based silicon rubber. Here's the relevant pages for these products. Here's the entire list of mold making rubbers BJB produces. http://bjbenterprises.com/index.php/...latinum-based/
    Find and study their on-line videos on how to use the stuff.

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ID:	98896 Typical metal casting rubber tools and various trees of metal parts. The tool is in the shape of a disc that splits into two halves -- a top and a bottom. The top half has a central sprue hole through which molten metal is poured after the disc has been brought up to speed. Centrifugal force pushes the molten metal outboard through connecting runners to the cavities that will give form to the metal as it changes state from liquid to solid; the white-metal freezes almost immediately.

    White-metal is the alloy of choice here as it is non-lead bearing, melts at about five-hundred degrees, and is readily available as 'leadless solder'. In this series of pictures you see the metal as bought, the rubber tool, freshly cast trees of parts, and in foreground those parts removed from the tool. The metal parts are then snipped off and bagged for sale.

    Note that inserts, placed into some of the tools cavities, are bonded to the cast metal parts. Like resin casting it's possible to combine pre-formed or non-substrate items with the casting medium so that they become one once the casting cycle is complete. Or, cores can be inserted such as greased brass rods, that when extracted from the cast parts form bores in the parts that can later accept control surface operating shafts, mechanical fasteners, or bores in propeller hubs to accept propeller shafts.

    Metal casting produces parts quickly, parts of considerable strength, and even the smallest item can be produced.
    (there is a practical limit to the cross-section of resin cast parts owing to the fact that catalyzed resin requires self-generated heat to make the state change -- not so with metal that freezes at room temperature).

    Below I'll cover the manufacture of a spin-casting tool, one of two metal casting tools, used to produce the cast metal parts for the defunct 1/72 FOXTROT kit .
    ... I'm going to get some utility out of that failed project, if it kills me! So, why not this term-paper?

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ID:	98897 Above you see two cast white-metal propellers for the never-to-see-daylight 1/72 FOXTROT kit we started development on. You see a left-hand and a right-hand pitched model propellers atop a photo of a prototype FOXTROT. Just to give some insight in how close I was able to re-create this submarines propellers in model form. The tool making process is simple. Master making is hard. Master making IS model building. But ... that's a whole other story.

    OK, some tool making 101:
    Attached Files
    Last edited by He Who Shall Not Be Named; 06-24-2015, 11:11 PM.

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